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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2019	Feb. 21, 2020	Jun. 28, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Trading Symbol	SRPT
Entity Registrant Name	Sarepta Therapeutics, Inc.
Entity Central Index Key	0000873303
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity File Number	001-14895
Entity Tax Identification Number	93-0797222
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	215 First Street
Entity Address, Address Line Two	Suite 415
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	274-4000
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, $0.0001 par value
Security Exchange Name	NASDAQ
Document Annual Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		77,776,779
Entity Public Float			$ 11,294,104,196
Documents Incorporated by Reference	The registrant has incorporated by reference into Part II and Part III of this Annual Report on Form 10-K portions of its definitive Proxy Statement for the 2020 Annual Meeting of Stockholders to be filed no later than 120 days after the end of the fiscal year covered by this Annual Report on Form 10-K.

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 835,080	$ 370,829
Short-term investments	289,668	803,083
Accounts receivable	90,879	49,044
Inventory	171,379	125,445
Other current assets	81,907	77,782
Total current assets	1,468,913	1,426,183
Property and equipment, net	129,620	97,024
Intangible assets, net	12,497	11,574
Right of use assets, net	37,933
Other non-current assets	173,859	107,294
Total assets	1,822,822	1,642,075
Current liabilities:
Accounts payable	68,094	33,829
Accrued expenses	185,527	134,095
Other current liabilities	11,146	5,766
Total current liabilities	264,767	173,690
Long-term debt	681,900	420,554
Lease liabilities	47,720
Other non-current liabilities	10,248	15,555
Total liabilities	1,004,635	609,799
Commitments and contingencies (Note 21)
Stockholders’ equity:
Preferred stock, $.0001 par value, 3,333,333 shares authorized; none issued and outstanding
Common stock, $.0001 par value, 99,000,000 shares authorized; 75,184,863 and 71,071,887 issued and outstanding at December 31, 2019 and 2018, respectively	8	7
Additional paid-in capital	3,112,130	2,611,294
Accumulated other comprehensive income (loss), net of tax	50	(99)
Accumulated deficit	(2,294,001)	(1,578,926)
Total stockholders’ equity	818,187	1,032,276
Total liabilities and stockholders’ equity	$ 1,822,822	$ 1,642,075

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	3,333,333	3,333,333
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	99,000,000	99,000,000
Common stock, issued	75,184,863	71,071,887
Common stock, outstanding	75,184,863	71,071,887

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Product, net	$ 380,833	$ 301,034	$ 154,584
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Total revenues	$ 380,833	$ 301,034	$ 154,584
Cost and expenses:
Cost of sales (excluding amortization of in-licensed rights)	56,586	34,193	7,353
Research and development	560,909	401,843	166,707
Selling, general and administrative	284,812	207,761	122,682
Acquired in-process research and development	173,240
Settlement and license charges	10,000		28,427
Amortization of in-licensed rights	849	865	1,053
Total cost and expenses	1,086,396	644,662	326,222
Operating loss	(705,563)	(343,628)	(171,638)
Other (loss) income:
Other expense, net	(8,317)	(18,982)	(1,990)
Gain from sale of Priority Review Voucher			125,000
Total other (loss) income	(8,317)	(18,982)	123,010
Loss before income tax expense (benefit)	(713,880)	(362,610)	(48,628)
Income tax expense (benefit)	1,195	(692)	2,060
Net loss	(715,075)	(361,918)	(50,688)
Other comprehensive loss:
Unrealized gains (losses) on investments	149	280	(259)
Total other comprehensive income (loss)	149	280	(259)
Comprehensive loss	$ (714,926)	$ (361,638)	$ (50,947)
Net loss per share — basic and diluted	$ (9.71)	$ (5.46)	$ (0.86)
Weighted average number of shares of common stock used in computing basic and diluted net loss per share	73,615,000	66,250,000	58,818,000

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive (Loss) Gain [Member]	Accumulated Deficit [Member]
BALANCE at Dec. 31, 2016	$ 336,691	$ 5	$ 1,503,126	$ (120)	$ (1,166,320)
BALANCE (in shares) at Dec. 31, 2016		54,759,000
Exercise of options for common stock	$ 13,799		13,799
Exercise of options for common stock, shares	792,845	793,000
Grant of restricted stock awards and vest of restricted stock units, net of cancellations, shares		400,000
Shares withheld for taxes	$ (2,227)		(2,227)
Shares withheld for taxes, shares		(60,000)
Issuance of common stock for cash, net of offering costs	353,959	$ 1	353,958
Issuance of common stock for cash, net of offering costs, shares		8,798,000
Issuance of common stock under employee stock purchase plan	1,425		1,425
Issuance of common stock under employee stock purchase plan, shares		102,000
Equity component of convertible notes	156,953		156,953
Purchase of capped call share options	(50,901)		(50,901)
Stock-based compensation	30,465		30,465
Unrealized gain (loss) from available-for-sale securities	(259)			(259)
Net loss	(50,688)				(50,688)
BALANCE at Dec. 31, 2017	789,217	$ 6	2,006,598	(379)	(1,217,008)
BALANCE (in shares) at Dec. 31, 2017		64,792,000
Exercise of options for common stock	$ 47,916		47,916
Exercise of options for common stock, shares	2,119,306	2,119,000
Grant of restricted stock awards and vest of restricted stock units, net of cancellations, shares		58,000
Shares withheld for taxes	$ (9,061)		(9,061)
Shares withheld for taxes, shares		(79,000)
Issuance of common stock for cash, net of offering costs	513,409	$ 1	513,408
Issuance of common stock for cash, net of offering costs, shares		4,107,000
Issuance of common stock under employee stock purchase plan	2,306		2,306
Issuance of common stock under employee stock purchase plan, shares		75,000
Stock-based compensation	50,127		50,127
Unrealized gain (loss) from available-for-sale securities	280			280
Net loss	(361,918)				(361,918)
BALANCE at Dec. 31, 2018	$ 1,032,276	$ 7	2,611,294	(99)	(1,578,926)
BALANCE (in shares) at Dec. 31, 2018		71,072,000
Exercise of options for common stock, shares	1,055,715
Exercise of options and stock appreciation rights for common stock	$ 31,522		31,522
Exercise of options and stock appreciation rights for common stock, shares		1,125,000
Grant of restricted stock awards and vest of restricted stock units, net of cancellations, shares		68,000
Shares withheld for taxes	(9,135)		(9,135)
Shares withheld for taxes, shares		(78,000)
Issuance of common stock for cash, net of offering costs	365,354	$ 1	365,353
Issuance of common stock for cash, net of offering costs, shares		2,604,000
Issuance of common stock for collaboration agreement	29,415		29,415
Issuance of common stock for collaboration agreement, shares		302,000
Issuance of common stock under employee stock purchase plan	5,079		5,079
Issuance of common stock under employee stock purchase plan, shares		92,000
Stock-based compensation	78,602		78,602
Unrealized gain (loss) from available-for-sale securities	149			149
Net loss	(715,075)				(715,075)
BALANCE at Dec. 31, 2019	$ 818,187	$ 8	$ 3,112,130	$ 50	$ (2,294,001)
BALANCE (in shares) at Dec. 31, 2019		75,185,000

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (715,075)	$ (361,918)	$ (50,688)
Adjustments to reconcile net loss to cash flows in operating activities:
Acquired in-process research and development	173,240
Non-cash up-front payment to StrideBio	29,415
Gain from sale of Priority Review Voucher			(125,000)
Depreciation and amortization	30,547	12,245	8,092
Amortization of investment discount	(8,445)	(7,672)	(888)
Loss from debt extinguishment		2,322
Non-cash interest expense	21,444	20,190	2,679
Stock-based compensation	78,602	50,127	30,465
Other	690	3,938	805
Changes in operating assets and liabilities, net:
Net increase in accounts receivable	(41,835)	(19,576)	(24,240)
Net increase in inventory	(45,934)	(41,840)	(70,792)
Net increase in other assets	(102,091)	(136,638)	(15,354)
Net increase in accounts payable, accrued expenses, lease liabilities and other liabilities	122,979	90,162	12,925
Net cash used in operations	(456,463)	(388,660)	(231,996)
Cash flows from investing activities:
Purchase of property and equipment	(59,631)	(61,157)	(12,000)
Purchase of intangible assets	(3,082)	(3,188)	(9,215)
Purchase of available-for-sale securities	(1,193,632)	(1,171,603)	(589,520)
Maturity and sales of available-for-sale securities	1,715,626	865,813	296,225
Proceeds from sale of Priority Review Voucher			125,000
Purchase of restricted investment		(353)
Maturity of restricted investment			10,695
Acquisition of Myonexus Therapeutics, Inc., net of cash acquired	(172,556)
Net cash provided (used) in investing activities	286,725	(370,488)	(178,815)
Cash flows from financing activities:
Proceeds from exercise of options and employee stock purchase program	36,601	50,222	15,224
Taxes paid related to net share settlement of equity awards	(4,337)
Proceeds from sales of common stock, net of offering costs	365,354	513,409	353,959
Repayment of June 2015 and July 2017 Term Loan		(30,000)	(15,000)
Proceeds from revolving line of credit		235,872	39,708
Repayment of revolving line of credit		(235,954)	(39,645)
Payment for debt extinguishment		(2,134)
Repayment of mortgage loans and notes payable		(1,265)	(109)
Purchase of capped call options			(50,901)
Proceeds from convertible debt offering			570,000
Debt issuance costs	(689)		(15,154)
Net cash provided by financing activities	642,554	530,150	888,082
Increase (decrease) in cash and cash equivalents	472,816	(228,998)	477,271
Cash, cash equivalents and restricted cash:
Beginning of period	370,829	599,827	122,556
End of period	843,645	370,829	599,827
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	835,080	$ 370,829	599,691
Restricted cash in other assets	8,565		$ 136
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]		us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash	843,645	$ 370,829	$ 599,827
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	8,550	11,308	1,912
Cash paid during the period for income taxes	933	1,548	5,336
Supplemental schedule of non-cash investing activities and financing activities:
Shares withheld for tax included in accrued expenses	4,798
Accrued debt discount and issuance costs	5,000		625
Property and equipment included in accrued expenses	1,181	5,421	2,525
Reclassification of long term investments to short term investments		$ 9,980
December 2019 Term Loan [Member]
Cash flows from financing activities:
Proceeds from Term Loan	$ 245,625
July 2017 Term Loan [Member]
Cash flows from financing activities:
Proceeds from Term Loan			$ 30,000

ORGANIZATION AND NATURE OF BUSINESS

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

ORGANIZATION AND NATURE OF BUSINESS

1. ORGANIZATION AND NATURE OF BUSINESS

Sarepta Therapeutics, Inc. (together with its wholly-owned subsidiaries, “Sarepta” or the “Company”) is a commercial-stage biopharmaceutical company focused on helping patients through the discovery and development of unique RNA-targeted therapeutics, gene therapy and other genetic therapeutic modalities for the treatment of rare diseases. Applying its proprietary, highly-differentiated and innovative technologies, and through collaborations with its strategic partners, the Company is developing potential therapeutic candidates for a broad range of diseases and disorders, including Duchenne muscular dystrophy (“DMD”), Limb-girdle muscular dystrophies (“LGMDs”), Mucopolysaccharidosis type IIIA (“MPS IIIA”) and other neuromuscular and central nervous system (“CNS”) disorders.

Its first and second commercial products in the U.S., EXONDYS 51 (eteplirsen) Injection (“EXONDYS 51”) and VYONDYS 53 (golodirsen) Injection (“VYONDYS 53”), respectively, were granted accelerated approval by the U.S. Food and Drug Administration (“FDA”) on September 19, 2016 and December 12, 2019, respectively. EXONDYS 51 and VYONDYS 53 are indicated for the treatment of DMD in patients who have a confirmed mutation of the DMD gene that is amenable to exon 51 and exon 53 skipping, respectively. EXONDYS 51 and VYONDYS 53 use the Company’s phosphorodiamidate morpholino oligomer (“PMO”) chemistry and exon-skipping technology to skip exon 51 and exon 53, respectively, of the dystrophin gene. Exon skipping is intended to promote the production of an internally truncated but functional dystrophin protein.

As of December 31, 2019, the Company had approximately $1,134.4 million of cash, cash equivalents and investments, consisting of $835.1 million of cash and cash equivalents, $289.7 million of short-term investments, and $9.6 million of restricted cash and investments. The Company believes that its balance of cash, cash equivalents and investments as of December 31, 2019 is sufficient to fund its current operational plan for at least the next twelve months, though it may pursue additional cash resources through public or private debt and equity financings, seek additional government contracts and establish collaborations with or license its technology to other companies.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENT ACCOUNTING PRONOUNCEMENTS

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENT ACCOUNTING PRONOUNCEMENTS

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENT ACCOUNTING PRONOUNCEMENTS

Basis of Presentation

The accompanying consolidated financial statements, which have been prepared in accordance with accounting principles generally accepted in the U.S. (“U.S. GAAP”), reflect the accounts of Sarepta Therapeutics, Inc. and its wholly-owned subsidiaries. All intercompany transactions between and among its consolidated subsidiaries have been eliminated. Management has determined that the Company operates in one segment: helping patients through the discovery and development of unique RNA-targeted therapeutics, gene therapy and other genetic therapeutic modalities for the treatment of rare diseases. The Company’s CEO, as the chief operating decision-maker, manages and allocates resources to the operations of the Company on a total company basis. The Company’s research and development organization is responsible for the research and discovery of new product candidates and supports development and registration efforts for potential future products. The Company’s supply chain organization manages the development of the manufacturing processes, clinical trial supply and commercial product supply. The Company’s commercial organization is responsible for commercialization of EXONDYS 51 and VYONDYS 53 in the U.S. and internationally. The Company is supported by other back-office general and administration functions. Consistent with this decision-making process, the Company’s CEO uses consolidated, single-segment financial information for purposes of evaluating performance, forecasting future period financial results, allocating resources and setting incentive targets.

Estimates and Uncertainties

The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, equity, revenue, expenses and the disclosure of contingent assets and liabilities. Actual results could differ from those estimates.

Fair Value Measurements

The Company has certain financial assets that are recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements:

•

Level 1—quoted prices for identical instruments in active markets;

•

Level 2—quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs and significant value drivers are observable in active markets; and

•

Level 3—valuations derived from valuation techniques in which one or more significant value drivers are unobservable.

The fair value of the majority of the Company’s financial assets is categorized as Level 1 within the fair value hierarchy. These assets include money market funds, publicly traded debt, and equity securities. For additional information related to fair value measurements, please read Note 5, Fair Value Measurements to the consolidated financial statements.

Cash Equivalents

Only investments that are highly liquid and readily convertible to cash and have original maturities of three months or less are considered cash equivalents.

Investments

Available-For-Sale Debt Securities

Available-for-sale debt securities are recorded at fair value and unrealized gains and losses are included in accumulated other comprehensive income (loss) in stockholder’s equity. Realized gains and losses are reported in other expense, net, on a specific identification basis.

Equity Investments

The Company’s equity investments include its investments in a publicly traded biotechnology company and a privately held biotechnology company and are included in other non-current assets in the Company’s consolidated balance sheets. The equity investment in the publicly traded biotechnology company has a readily determinable fair value and is carried at fair value with changes in value recorded as a gain or loss in the Company’s consolidated statements of operations and comprehensive loss. The equity investment in the privately held biotechnology company does not have readily determinable fair value and is measured at cost less any impairment, plus or minus changes resulting from observable price changes for the identical or a similar investment of the same issuer, which is recorded as a gain or loss on the Company’s consolidated statements of operations and comprehensive loss.

Accounts Receivable

The Company’s accounts receivable primarily arise from product sales. They are generally stated at the invoiced amount and do not bear interest. Revenues from product sales are recorded at the net sales price (transaction price), which includes estimates of variable consideration for which reserves are established and which result from Medicaid rebates, governmental chargebacks including Public Health Services (“PHS”) chargebacks, prompt pay discounts, co-pay assistance and distribution fees. These reserves are based on the amounts earned or to be claimed on the related sales and are classified as reductions of accounts receivable (if no payments are required of the Company) for PHS chargebacks, prompt pay discounts and certain distribution fees, or a current liability (if a payment is required of us), for Medicaid rebates, co-pay assistance and certain distribution fees.

The accounts receivable from product sales represents receivables due from the Company’s specialty distributor and specialty pharmacies in the U.S. as well as certain distributors in the EU, Brazil, Israel and the Middle East. The Company monitors the financial performance and creditworthiness of its customers so that it can properly assess and respond to changes in the customers’ credit profiles. The Company provides reserves against trade receivables for estimated losses that may result from a customer’s inability to pay. Amounts determined to be uncollectible are written-off against the established reserve. As of December 31, 2019, the credit profiles for the Company’s customers are deemed to be in good standing and an allowance for doubtful accounts receivable is not considered necessary.

Concentration of Credit Risk

Financial instruments which potentially subject the Company to concentrations of credit risk consist of accounts receivable from customers and cash, cash equivalent and investments held at financial institutions.

For the year ended December 31, 2019, the majority of the Company’s accounts receivable arose from product sales in the U.S. and all customers have standard payment terms which generally require payment within 60 to 91 days. Outside of the U.S., the payment terms range between 45 and 150 days. Three individual customers accounted for 43%, 41% and 13% of net product revenues for the year ended December 31, 2019, 42%, 38% and 18% for the year ended December 31, 2018, and 47%, 34% and 19% for the year ended December 31, 2017. Three individual customers accounted for 45%, 37% and 11% of accounts receivable from product sales for the year ended December 31, 2019 and 51%, 28% and 10% for the year ended December 31, 2018. As of December 31, 2019, the Company believes that such customers are of high credit quality.

As of December 31, 2019, the Company’s cash equivalents and investments were concentrated at three financial institutions. The Company does not believe that there is significant risk of non-performance by the financial institutions.

Inventories

Inventories are stated at the lower of cost and net realizable value with cost determined on a first-in, first-out basis. The Company capitalizes inventory costs associated with products following regulatory approval when future commercialization is considered probable and the future economic benefit is expected to be realized. EXONDYS 51 and VYONDYS 53 inventory that may be used in clinical development programs is charged to research and development expense when the product enters the research and development process and no longer can be used for commercial purposes.

The Company periodically reviews its inventories for excess amounts or obsolescence and writes down obsolete or otherwise unmarketable inventory to its estimated net realizable value. Additionally, though the Company’s product is subject to strict quality control and monitoring which it performs throughout the manufacturing processes, certain batches or units of product may not meet quality specifications resulting in a charge to cost of sales.

For products which are under development and have not yet been approved by regulatory authorities, purchased drug product is charged to research and development expense upon delivery. Delivery occurs when the inventory passes quality inspection and ownership transfers to the Company. Nonrefundable advance payments for research and development activities, including production of purchased drug product, are deferred and capitalized until the goods are delivered. If the Company does not expect the goods to be delivered or services to be rendered, the advanced payment capitalized will be charged to expense.

Property and Equipment

Property and equipment are initially recorded at cost, including the acquisition cost and all costs necessarily incurred to bring the asset to the location and working condition necessary for its intended use. The cost of normal, recurring or periodic repairs and maintenance activities related to property and equipment are expensed as incurred. The cost for planned major maintenance activities, including the related acquisition or construction of assets, is capitalized if the repair will result in future economic benefits. Interest costs incurred during the construction period of major capital projects are capitalized until the asset is ready for its intended use, at which point the interest costs are amortized as depreciation expense over the life of the underlying asset.

The Company generally depreciates the cost of its property and equipment using the straight-line method over the estimated useful lives of the respective assets, which are summarized as follows:

Asset Category		Useful lives
Lab equipment		5 years
Office equipment		5 years
Software and computer equipment		3 - 5 years
Furniture and fixtures		7 years
Leasehold improvements		Lesser of the useful life or the term of the respective lease
Land improvements		25 years
Land		Not depreciated
Building and improvements		30 years
Construction in Progress		Not depreciated until put into service

Intangible assets

The Company’s intangible assets consist of in-licensed rights, patent costs, and software licenses, which are stated in the Company’s consolidated balance sheets net of accumulated amortization and impairments, if applicable.

The in-licensed rights relate to agreements with BioMarin Pharmaceutical, Inc. (“BioMarin”) and the University of Western Australia (“UWA”). The in-licensed rights are being amortized on a straight-line basis over the remaining life of the related patents because the life of the related patents reflects the expected time period that the Company will benefit from the in-licensed rights.

Patent costs consist primarily of external legal costs, filing fees incurred to file patent applications and renewal fees on proprietary technology developed or licensed by the Company. Patent costs associated with applying for a patent, being issued a patent and annual renewal fees are capitalized. Costs to defend a patent and costs to invalidate a competitor’s patent or patent application are expensed as incurred. Patent costs are amortized on a straight-line basis over the shorter of the estimated economic lives or the initial term of the patents, which is generally 20 years.

Impairment of Long-Lived Assets

Long-lived assets held and used by the Company, intangible assets with definite lives and equity investments without a readily determinable fair value are reviewed for impairment whenever events or circumstances indicate that the carrying amount of assets may not be recoverable. The Company evaluates recoverability of assets to be held and used by comparing the carrying amount of an asset to future net undiscounted cash flows to be generated by the asset. If the asset is considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the fair value of the assets. Such reviews assess the fair value of the assets based upon estimates of future cash flows that the assets are expected to generate.

Convertible Debt

The Company separately accounts for the liability and equity components of convertible debt instruments that can be settled in cash by allocating the proceeds from issuance between the liability component and the embedded conversion option. The value of the equity component is calculated by first measuring the fair value of the liability component, using the interest rate of a similar liability that does not have a conversion feature, as of the issuance date. The difference between the proceeds from the convertible debt issuance and the amount measured as the liability component is recorded as the equity component with a corresponding discount recorded on the debt. The Company recognizes the amortization of the resulting discount as interest expense using the effective interest method. Simultaneously, the Company bought capped call options from certain counterparties to minimize the impact of potential dilution upon conversion. The premium for the capped call options was recorded as additional paid-in capital. For additional information related to the convertible debt transactions, please read Note 13, Indebtedness to the consolidated financial statements.

Revenue Recognition

The Company recognizes revenue when a customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for the goods or services provided. To determine revenue recognition for arrangements within the scope of ASC Topic 606, “Revenue from Contracts with Customers” (“ASC Topic 606”), the Company performs the following five steps: (1) identify the contract with the customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when or as the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers or provides to the customer. At contract inception, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when or as the performance obligation is satisfied. The only performance obligation in the Company’s contracts with customers is to timely deliver drug products to the customer’s designated location.

Product revenues

The Company distributes its products principally through its customers. The customers subsequently resell the product to patients and health care providers. The Company provides no right of return to the customers except in cases of shipping error or product defect. Product revenues are recognized when the customers take control of the product, which typically occurs upon delivery to the customers. For the years ended December 31, 2019, 2018 and 2017, the majority of the revenues recognized were generated by the specialty distributor and specialty pharmacies in the U.S.

Variable Consideration

Product revenues are recorded at the net sales price (transaction price) which includes estimated reserves for variable consideration, such as Medicaid rebates, governmental chargebacks, including Public Health Service (“PHS”) chargebacks, prompt payment discounts, co-pay assistance and distribution fees. These reserves reflect the Company’s best estimates of the amount of consideration to which it is entitled based on the terms of the contracts. Additional details relating to variable consideration follows:

•

Medicaid rebates relate to the Company’s estimated obligations to states under established reimbursement arrangements. Medicaid rebate reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a liability which is included in accrued expenses.

•

Governmental chargebacks, including PHS chargebacks, relate to the Company’s estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices that the Company charges to wholesalers. The wholesaler charges the Company for the difference between what the wholesaler pays for the products and the ultimate selling price to the qualified healthcare providers. Chargeback reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and accounts receivable. Chargeback amounts are generally determined at the time of resale to the qualified healthcare provider from the wholesaler, and the Company generally issues credits for such amounts within a few weeks of receiving notification of resale from the wholesaler.

•

Prompt payment discounts relate to the Company’s estimated obligations for credits to be granted to specialty pharmacies for remitting payment on their purchases within established incentive periods. Reserves for prompt payment discounts are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and accounts receivable.

•

Co-pay assistance relates to financial assistance provided to qualified patients, whereby the Company may assist them with prescription drug co-payments required by the patient’s insurance provider. Reserves for co-pay assistance are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a liability which is included in accrued expenses.

•

Distribution fees relate to fees paid to customers in the distribution channel that provide the Company with inventory management, data and distribution services and are generally accounted for as a reduction of revenue. To the extent that the services received are distinct from the Company’s sale of products to the customers, these payments are accounted for as selling, general and administrative expenses. Reserves for distribution fees result in an increase in a liability if payments are required of the Company or a reduction of accounts receivable if no payments are required of the Company.

Research and Development

Research and development expenses consist of costs associated with research activities as well as those with the Company’s product development efforts, conducting pre-clinical trials, clinical trials and manufacturing activities. Research and development expenses are expensed as incurred. Up-front fees and milestones paid to third parties in connection with technologies which have not reached technological feasibility and do not have an alternative future use are expensed when incurred.

Direct research and development expenses associated with the Company’s programs include clinical trial site costs, clinical manufacturing costs, costs incurred for consultants and other external services, such as data management and statistical analysis support and materials and supplies used in support of clinical programs. Indirect costs of the Company’s clinical programs include salaries, stock-based compensation and an allocation of its facility and technology costs.

When third-party service providers’ billing terms do not coincide with the Company’s period-end, the Company is required to make estimates of its obligations to those third parties, including clinical trial and pharmaceutical development costs, contractual services costs and costs for supply of its drug candidates, incurred in a given accounting period and record accruals at the end of the period. The Company bases its estimates on its knowledge of the research and development programs, services performed for the period, past history for related activities and the expected duration of the third-party service contract, where applicable.

Stock-Based Compensation

The Company’s stock-based compensation programs include stock options, restricted stock awards (“RSAs”), restricted stock units (“RSUs”), stock appreciation rights (“SARs”) and an employee stock purchase program (“ESPP”). The Company accounts for stock-based compensation using the fair value method.

The fair values of stock options and SARs are estimated on the date of grant using the Black-Scholes-Merton option-pricing model. The fair values of RSAs and RSUs are based on the fair market value of the Company’s common stock on the date of the grant. The fair value of stock awards, with consideration given to estimated forfeitures, is recognized as stock-based compensation expense on a straight-line basis over the vesting period of the grants. For stock awards with performance-vesting conditions, the Company does not recognize compensation expense until it is probable that the performance-vesting condition will be achieved.

Under the Company’s ESPP, participating employees purchase common stock through payroll deductions. The purchase price is equal to 85% of the lower of the closing price of the Company’s common stock on the first business day and the last business day of the relevant purchase period. The fair value of stock purchase rights are estimated using the Black-Scholes-Merton option-pricing model. The fair value of the look-back provision with the 15% discount is recognized on a graded-vesting basis as stock-based compensation expense over the purchase period.

In addition to stock options with service and performance conditions, the Company also granted its CEO options with service and market conditions. A market condition relates to the achievement of a specified price of the Company’s common stock, a specified amount of intrinsic value indexed to the Company’s common stock or a specified price of the Company’s common stock in terms of other similar equity shares. The grant date fair value for the options with service and market conditions is determined by a lattice model with Monte Carlo simulations and is recognized as stock-based compensation expense on a straight-line basis over the service period.

Income Taxes

The Company follows the asset and liability method of accounting for income taxes. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the consolidated financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. It is the intention of the Company to reinvest the earnings of its non-U.S. subsidiaries in those operations and not to repatriate the earnings to the U.S. Accordingly, the Company does not provide for deferred taxes on the excess of the financial reporting over the tax basis in its investments in foreign subsidiaries as they are considered permanent in duration.

Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered and settled. A valuation allowance is recorded to reduce the net deferred tax asset to zero when it is more likely than not that the net deferred tax asset will not be realized. The Company recognizes the effect of income tax positions only if those positions are more likely than not of being sustained upon an examination.

Leases

Effective January 1, 2019, the Company adopted ASC Topic 842, “Leases” (“ASC 842”), using the modified retrospective approach and utilizing the effective date as its date of initial application, for which prior periods are presented in accordance with the previous guidance in ASC Topic 840, “Leases” (“ASC 840”).

As a result of adopting ASC 842, the Company recorded lease right-of-use (“ROU”) assets of $42.5 million and lease liabilities of $60.1 million as of January 1, 2019, primarily related to real estate leases, based on the present value of future lease payments on the date of adoption. The difference between the ROU assets and lease liabilities was due to previously recorded net deferred rent liabilities that were reclassified into the ROU assets. There was no impact to retained earnings upon adoption of ASC 842. Amounts related to finance leases were immaterial as of adoption .

At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than 12 months are recognized on the balance sheet as ROU assets and short-term and long-term lease liabilities, as applicable. The Company has elected not to recognize on the balance sheet leases with terms of 12 months or less. The Company typically only includes an initial lease term in its assessment of a lease arrangement. Options to renew a lease are not included in the Company’s assessment unless there is reasonable certainty that the Company will renew. The Company monitors its plans to renew its leases no less than on a quarterly basis. In addition, the Company’s lease agreements generally do not contain any residual value guarantees or restrictive covenants.

Operating lease liabilities and their corresponding ROU assets are recorded based on the present value of future lease payments over the expected remaining lease term at lease commencement. Lease cost for operating leases is recognized on a straight-line basis over the lease term as an operating expense. Certain adjustments to the ROU asset may be required for items such as lease prepayments or incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate, which reflects the fixed rate at which the Company could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. In transition to ASC 842, the Company utilized the remaining lease term of its leases in determining the appropriate incremental borrowing rate.

In accordance with ASC 842, components of a lease should be bifurcated between lease components and non-lease components. The fixed and in-substance fixed contract consideration identified must then be allocated based on the respective relative fair values to the lease components and non-lease components. However, ASC 842 provides a practical expedient that allows an accounting policy election to not separate lease and non-lease components by class of underlying asset. In using this expedient, the lease component and non-lease components are accounted for together as a single component. For real estate leases, the Company has elected to account for the lease and non-lease components together for existing classes of underlying assets and allocates the contract consideration to the lease component only. This practical expedient is not elected for manufacturing facilities and equipment embedded in product supply arrangements.

Embedded Derivatives

The Company evaluates certain of its financial and business development transactions to determine if embedded components of these contracts meet the definition of derivative under Topic ASC 815, “Derivatives and Hedging”. In general, embedded derivatives are required to be bifurcated from the host instrument if (i) the embedded feature is not clearly and closely related to the host contract and (ii) the embedded feature, if considered a freestanding instrument, met the definition of a derivative. The embedded derivative is reported on the balance sheets at its fair value. Any change in fair value, as determined at each measurement period, is recorded as a component of the consolidated statements of operations and comprehensive loss.

Commitments and Contingencies

The Company records liabilities for legal and other contingencies when information available to the Company indicates that it is probable that a liability has been incurred and the amount of loss can be reasonably estimated. Legal costs in connection with legal and other contingencies are expensed as costs are incurred.

Recent Accounting Pronouncements

In December 2019, the Financial Accounting Standards Board (“FASB”) issued ASU 2019-12, “Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes”, which is intended to simplify the accounting for income taxes. This ASU removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The new standard will be effective beginning January 1, 2021. The Company is currently evaluating the potential impact this ASU may have on its financial position and results of operations upon adoption.

In November 2018, the FASB issued ASU 2018-18, “Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606”. The amendments in this update clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue when the collaborative arrangement participant is a customer in the context of a unit of account and precludes recognizing as revenue consideration received from a collaborative arrangement participant if the participant is not a customer. The new standard will be effective beginning January 1, 2020 and early adoption is permitted. As of December 31, 2019, the Company has elected to early adopt this ASU and the adoption did not have a material impact on its financial position and results of operations.

In August 2018, the FASB issued ASU No. 2018-13, “Fair Value Measurement (Topic 820), Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement”. This ASU removed the following disclosure requirements: (1) the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy; (2) the policy for timing of transfers between levels; and (3) the valuation processes for Level 3 fair value measurements. Additionally, this update added the following disclosure requirements: (1) the changes in unrealized gains and losses for the period included in other comprehensive income and loss for recurring Level 3 fair value measurements held at the end of the reporting period; (2) the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. For certain unobservable inputs, an entity may disclose other quantitative information (such as the median or arithmetic average) in lieu of the weighted average if the entity determines that other quantitative information would be a more reasonable and rational method to reflect the distribution of unobservable inputs used to develop Level 3 fair value measurements. ASU No. 2018-13 will be effective for fiscal years beginning after December 15, 2019 with early adoption permitted. As of December 31, 2019, the Company has not elected to early adopt this guidance but does not expect that the adoption of this guidance will have a material effect on its consolidated financial statements.

In August 2018, the FASB issued ASU No. 2018-15, “Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract”. This ASU requires a customer in a cloud computing arrangement (i.e., hosting arrangement) that is a service contract to follow the internal-use software guidance contained in ASC Subtopic 350-40 to determine which implementation costs to capitalize as assets or expense as incurred. Capitalized implementation costs related to a hosting arrangement that is a service contract will be amortized over the term of the hosting arrangement, beginning when the module or component of the hosting arrangement is ready for its intended use. ASU No. 2018-15 will be effective for fiscal years beginning after December 15, 2019, with early adoption permitted. As of December 31, 2019, the Company has not elected to early adopt this guidance but believes that the adoption of this guidance will not have a material effect on its consolidated financial statements.

In June 2016, the FASB issued ASU No. 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments”. This ASU requires that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and establishes additional disclosures related to credit risks. For available-for-sale debt securities with unrealized losses, this standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. ASU 2016-13 limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and requires the reversal of previously recognized credit losses if fair value increases. ASU 2016-13 will be effective for fiscal years beginning after December 15, 2019 with early adoption permitted, and requires adoption using a modified retrospective approach, with certain exceptions. As of December 31, 2019, the Company has not elected to early adopt this guidance. Based on the composition of the Company’s investment portfolio as of December 31, 2019, current market conditions and historical credit loss activity, the adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements. Additionally, for trade receivables, due to their short duration and the credit profile of the Company’s customers, the effect of transitioning from the incurred losses model to the expected losses model is not expected to be material.

LICENSE AND COLLABORATION AGREEMENTS

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

LICENSE AND COLLABORATION AGREEMENTS

3. LICENSE AND COLLABORATION AGREEMENTS

Roche Holding A.G.

On December 21, 2019, the Company entered into a license, collaboration and option agreement and a stock purchase agreement (collectively, the “Roche Agreements”) with F. Hoffman-La Roche Ltd (“Roche”), providing Roche with exclusive commercial rights to SRP-9001 (AAVrh74.MHCK7.micro-dystrophin) (the “Lead Product”), the Company’s investigational gene therapy for DMD, outside the U.S. The Company retains all rights to SRP-9001 in the U.S. and will perform all development activities directed to obtaining and maintaining regulatory approvals for SRP-9001 in the U.S. and the EU. Further, global development expenses for SRP-9001 will be equally shared between the two parties.

The closing of the transaction was subject to the expiration or termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 and other customary conditions. The agreement became effective as of February 4, 2020, and closed on February 14, 2020.

When the Roche Agreements became effective, the Company received payments totaling approximately $1.2 billion, consisting of $750.0 million in an up-front payment and $400.0 million in an equity investment. Additionally, the Company may receive up to approximately $1.7 billion in regulatory and sales milestones related to the Lead Product. Upon commercialization, the Company is also eligible to receive tiered royalty payments based on net sales.

In addition, Roche has options to in-license (1) certain exon-skipping products that target the dystrophin gene to induce exon skipping, including eteplirsen, golodirsen, casimersen and SRP-5051, (2) certain gene therapy products other than SRP-9001 that encode and directly express dystrophin or a derivative thereof and (3) certain gene-editing products that modify, repair, or activate an endogenous dysfunctional dystrophin gene (collectively, the “Option Products”). If and when Roche decides to exercise the options, it will be required to make an option exercise payment, on a per Option Product basis, in an amount ranging between $20.0 million and $125.0 million.

As of December 31, 2019, there was no accounting impact as a result of the execution of the Roche Agreements because the closing of the transaction did not occur until subsequent to year-end.

Genethon

In May 2017, the Company entered into a sponsored research agreement (the “Research Agreement”) with Genethon for its micro-dystrophin gene therapy program for the treatment of DMD. The Research Agreement provided the Company with an option to in-license the corresponding technology. On November 22, 2019, the Company exercised the option and entered into a license and collaboration with Genethon (the “Genethon Collaboration Agreement”). The Genethon Collaboration Agreement grants the Company with exclusive rights in the majority of the world (primarily excluding the EU) to Genethon’s micro-dystrophin gene therapy products (“Genethon Products”) and other micro-dystrophin gene therapy products (“Other Licensed Products”).

Under the Genethon Collaboration Agreement, a joint steering committee will be established to plan, monitor and coordinate development activities for Genethon Products and Other Licensed Products. The Company and Genethon will be responsible for 75% and 25%, respectively, of development costs related to both the Genethon Products and the Other Licensed Products. For the year ended December 31, 2019, the Company recorded $9.0 million of research and development expense related to reimbursable development costs incurred for Genethon Products to date.

Upon exercise of the option, the Company made an up-front payment of $28.0 million and may be liable for up to $157.5 million and $78.8 million in development, regulatory and sales milestones for the Genethon Products and Other Licensed Products, respectively. Furthermore, upon commercialization, the Company will be required to make tiered royalty payments based on net sales of the Genethon Products and the Other Licensed Products.

The up-front payment represents rights to potential future benefits associated with ongoing research and development activities that have no alternative future use. Accordingly, this amount has been recorded as research and development expense in the accompanying consolidated statements of operations and comprehensive loss for the year ended December 31, 2019. As of December 31, 2019, no development or regulatory milestones were deemed probable of being achieved and, accordingly, no additional expense has been recognized.

StrideBio, Inc.

On November 14, 2019 (the “StrideBio Effective Date”), the Company entered into a collaboration and license agreement (the “StrideBio Collaboration Agreement”) and a stock purchase agreement (collectively, the “StrideBio Agreements”) with StrideBio, Inc. (“StrideBio”). Under the terms of the StrideBio Collaboration Agreement, StrideBio granted the Company exclusive worldwide licenses to develop, collaborate and commercialize StrideBio’s adeno-associated viral capsids for gene therapy with respect to multiple initial development targets (“Initial Targets”), and, at the option of the Company, additional development targets (“Additional Targets”). The Company also may be required to participate in StrideBio’s next preferred equity round of financing, subject to certain conditions.

Both the Initial Targets and the Additional Targets are comprised of targets to which the Company will have the exclusive right to perform development activities (“Sarepta Development Targets”) and targets that the two parties will jointly develop through completion of Phase 1/2 clinical trials (“Joint Development Targets”). The Company also has the right to select additional Sarepta Development Targets and Joint Development Targets. For each Sarepta Development Target, StrideBio is responsible for initial research activities and each party bears its own costs while the Company is responsible for all costs following transfer of responsibilities to the Company for additional development. For each Joint Development Target, the parties will be responsible to develop a joint development plan for which the parties will share equally all costs through Phase 1/2 of clinical trials after which the Company will be solely responsible for the continued development, regulatory approval and commercialization of the target, including all related costs. The Company and StrideBio will also form a joint steering committee to oversee the collaboration activities.

As a result of execution of the StrideBio Agreements, the Company recognized an up-front expense of $46.9 million, consisting of a cash payment of $17.5 million and 301,980 shares of the Company’s common stock delivered to StrideBio equal to $29.4 million. For Sarepta Development Targets and Joint Development Targets, respectively, the Company may be liable for up to $450.0 million and $835.0 million in development, regulatory and sales milestone payments per target. Furthermore, the Company may be obligated to pay StrideBio up to $42.5 million in additional fees when and if Additional Targets are selected. Additionally, upon commercialization, the Company may be required to make tiered royalty payments based on net sales of each target.

The total up-front payment of $46.9 million, representing the fair value of the common shares delivered and cash, represents rights to potential future benefits associated with ongoing research and development activities that have no alternative future use. Accordingly, this amount has been recorded as research and development expense in the accompanying consolidated statements of operations and comprehensive loss for the year ended December 31, 2019. As of December 31, 2019, no development or regulatory milestones were deemed probable of being achieved and, accordingly, no additional expense has been recognized.

Myonexus Therapeutics

In May 2018, the Company entered into a Warrant to Purchase Common Stock Agreement (“Warrant Agreement”) with Myonexus Therapeutics, Inc. (“Myonexus”), a clinical-stage gene therapy biotechnology company that was developing gene therapies for Limb-Girdle muscular dystrophies (“LGMD”). Pursuant to the terms of the Warrant Agreement, the Company made an up-front payment of $60.0 million to purchase an exclusive option to acquire Myonexus for $200.0 million plus sales-related and regulatory-related contingent payments. During the year ended December 31, 2018, the Company recorded $85.0 million to research and development expense in connection with the Warrant Agreement comprised of the $60.0 million up-front payment, two development milestone payments totaling $20.0 million, and a third development milestone for $5.0 million was deemed probable of being achieved as of December 31, 2018.

On February 27, 2019, the Company announced that it exercised the exclusive option to acquire Myonexus. The final exercise price as negotiated between the Company and Myonexus was $165.0 million. In addition, the Company incurred transaction fees and other fees associated with the exercise of approximately $8.8 million. The Company may also be required to make up to $200.0 million in additional payments to selling shareholders of Myonexus based on the achievement of certain sales- and regulatory-related milestones. The acquisition closed on April 4, 2019.

As a result of the acquisition, the Company added five LGMD gene therapy programs, including MYO-101, MYO-102 and MYO-201 that are currently in Phase 1/2 clinical trials, to its research and development portfolio. The acquisition of Myonexus has been accounted for as an asset acquisition as substantially all of the fair value of the gross assets acquired is concentrated in a group of similar identifiable assets (the five LGMD gene therapy programs).

Additionally, the Company assessed whether any of the contingent payments met the definition of a derivative under ASC 815 and, therefore, should be accounted for as contingent consideration. The Company identified that one regulatory-related milestone (not solely based on drug approval by the FDA) met the definition of a derivative. As a result, the Company recorded a contingent consideration liability of $4.5 million at the acquisition date. Any changes in the fair value of the contingent consideration liability after the acquisition date is included in the Company’s statement of operations. This amount was estimated through a probability-weighted expected return method that incorporated industry-based probability adjusted assumptions relating to the achievement of the milestone and thus the likelihood of making the payments. This fair value measurement was based upon significant inputs not observable in the market and therefore represented a Level 3 fair value measurement. The Company did not assume any other liabilities as a result of the acquisition.

The following table summarizes the total consideration for the asset acquisition and the value of assets acquired and liability assumed:

Consideration (in thousands)
Purchase price	$	165,000
Transactions costs and other fees		8,753
Contingent consideration		4,500
Total consideration	$	178,253

Assets Acquired (in thousands)
Cash and cash equivalents	$	1,197
Prepaids		3,816
In-process research and development		173,240
Total assets acquired	$	178,253

Liability Assumed (in thousands)
Contingent consideration		4,500
Total liability assumed	$	4,500

The acquired in-process research and development asset relates to the LGMD asset group. Due to the stage of development of this asset group, significant risk remains, and it is not yet probable that there is future economic benefit from this asset. Absent successful clinical results and regulatory approval, there is no alternative future use associated with the LGMD asset group. Accordingly, the value of this asset of $173.2 million was immediately expensed to research and development expense during the three months ended June 30, 2019.

The portion of the $200.0 million in contingent payments related to the sales milestone will be accrued when and if the sales milestone becomes probable of being achieved, and the related payment will be capitalized and amortized over the life of the patent. As of December 31, 2019, the sales milestone was not probable of being achieved.

Lysogene S.A.

In October 2018, the Company entered into a license and collaboration agreement to develop and commercialize LYS-SAF302, a gene therapy to treat MPS IIIA as well as an equity investment agreement with Lysogene S.A. (“Lysogene”). Under the license and collaboration agreement, in addition to the payment of up-front fees, the Company may be liable for a total of $102.8 million in development, regulatory and sales milestones. Furthermore, the Company may be required to make tiered royalty payments based on net sales of the LYS-SAF302 product subsequent to its commercialization. Under the equity investment agreement, the Company purchased 950,606 shares of common stock issued by Lysogene, representing 8% of the outstanding equity of Lysogene at the time of the transaction.

As a result of execution of the agreements, for the year ended December 31, 2018, the Company recorded research and development expense of $44.8 million, consisting of $26.1 million related to the payment of up-front fees and $18.7 million related to the achievement of a development milestone. In addition, $1.9 million of the total up-front fees paid was allocated to the equity investment in Lysogene and recorded as an other non-current asset. Changes in the fair value of this equity investment are recorded to other (loss) income in the Company’s consolidated statements of operations and other comprehensive loss.

As of December 31, 2019, no additional development or regulatory milestones were deemed probable of being achieved and, accordingly, no additional expense has been recognized. Further, the changes in the fair value of the equity investment for the years ended December 31, 2019 and 2018 were not material.

Lacerta Therapeutics

In August 2018, the Company entered into a license, development and option agreement (the “Lacerta License Agreement”) and a Series A Preferred Stock Purchase Agreement (the “Stock Purchase Agreement”) with Lacerta Therapeutics, Inc. (“Lacerta”). Pursuant to the Lacerta License Agreement, the Company licensed exclusive worldwide rights to develop, manufacture and commercialize a pre-clinical Pompe product candidate (the “Pompe License”). Lacerta also granted the Company exclusive options to enter into exclusive license agreements to develop, manufacture and commercialize other gene therapy product candidates for Sanfilipo syndrome and L-Amino Acid Decarboxylase Deficiency for additional consideration of $42.0 million (collectively, the “Options”) when (and if) the Options are exercised. Additionally, the Company may be liable for up to approximately $44.0 million in development, regulatory and sales milestones associated with the Pompe License and may be required to make tiered royalty payments based on net sales of the Pompe product subsequent to its commercialization. Under the Stock Purchase Agreement, the Company purchased approximately 4.5 million shares of Series A preferred stock issued by Lacerta.

Under the agreements, the Company made an up-front payment of $38.0 million to Lacerta, $30.0 million and $8.0 million of which were allocated to the Series A preferred stock investment and the Pompe License, respectively. The amount allocated to the Pompe License represents rights to potential future benefits associated with ongoing research and development activities that have no alternative future use. Accordingly, this amount was recorded as research and development expense in the accompanying consolidated statements of operations and comprehensive loss for the year ended December 31, 2018. As of December 31, 2019, no development or regulatory milestones were deemed probable of being achieved and, accordingly, no additional expense has been recognized.

The $30.0 million allocated to the Series A preferred stock investment was initially measured at cost and is classified as an other non-current asset in the accompanying consolidated balance sheets. Changes in the carrying value of the investment are reported as a component of earnings whenever there are observable price changes in orderly transactions for identical or similar investments of Lacerta in the future. For the years ended December 31, 2019 and 2018, the Company did not record any changes in carrying value of the investment as Lacerta did not issue identical or similar shares during the corresponding periods.

Nationwide Children’s Hospital

In December 2016, the Company entered into an exclusive option agreement with Nationwide Children’s Hospital (“Nationwide”) from which the Company obtained an exclusive right to acquire a worldwide license of the micro-dystrophin gene therapy technology for DMD and Becker muscular dystrophy. In October 2018, the Company exercised the option and entered into a license agreement with Nationwide (“Nationwide License Agreement”). Pursuant to the Nationwide License Agreement, the Company licensed exclusive worldwide rights to develop, manufacture and commercialize micro-dystrophin gene therapy product candidates. Under the agreement, the Company made an up-front payment of $1.0 million to Nationwide, which was recorded as research and development expense in the accompanying consolidated statements of operations and comprehensive loss for the year ended December 31, 2018. Additionally, the Company may be required to make up to $29.0 million in development, regulatory and sales milestone payments per micro-dystrophin product and low-single-digit royalty payments based on net sales of the micro-dystrophin products upon commercialization. As of December 31, 2019, no development or regulatory milestones were deemed probable of being achieved and, accordingly, no additional expense has been recognized.

BioMarin Pharmaceutical, Inc.

In July 2017, the Company and the University of Western Australia (“UWA”) entered into a settlement agreement with BioMarin Pharmaceutical, Inc. (“BioMarin”). On the same day, the Company entered into a license agreement, which was subsequently amended in April 2019, with BioMarin and Academisch Ziekenhuis Leiden (“AZL”) (collectively with the Company, UWA and BioMarin, the “Settlement Parties”). Under these agreements and amendment, BioMarin agreed to provide the Company with an exclusive license to certain intellectual property with an option to convert the exclusive license into a co-exclusive license and the Settlement Parties agreed to stop most existing efforts to continue with ongoing litigation and opposition and other administrative proceedings concerning BioMarin’s intellectual property. As a result of execution of the agreements, the Company made total up-front payments of $35.0 million. Additionally, the Company may be liable for up to approximately $65.0 million in regulatory and sales milestones for eteplirsen as well as casimersen and golodirsen. BioMarin is also eligible to receive tiered royalty payments, ranging from 4% to 8%, based on the net sales for the two products and product candidate. The royalty terms under the license agreement will expire in March 2024 in the U.S., December 2024 in the EU and no later than December 2024 in other countries.

Of the $35.0 million paid to BioMarin, $28.4 million was expensed as incurred and $6.6 million was recorded as an intangible asset, representing the fair value of the U.S. license to BioMarin’s intellectual property. The intangible asset is being amortized on a straight-line basis over the remaining life of the patent and has a carrying value of $4.2 million as of December 31, 2019.

The FDA approval of VYONDYS 53 in December 2019 resulted in a settlement charge to BioMarin of $10.0 million and has been expensed as incurred. No regulatory or sales milestones were achieved for the years ended December 31, 2018 or 2017. For the years ended December 31, 2019, 2018 and 2017, the Company recognized royalty expense of $19.4 million, $15.1 million and $4.7 million, respectively. As of December 31, 2019, no other regulatory or sales milestones were deemed probable of being achieved and, accordingly, no additional in-licensed rights or expenses have been recognized.

University of Western Australia

In April 2013, the Company and UWA entered into an amendment to an existing exclusive license agreement relating to the treatment of DMD by inducing the skipping of certain exons. The agreement was further amended in June 2016. Under the amended agreement, the Company may be obligated to make payments to UWA totaling up to $26.0 million upon the achievement of certain development, regulatory and sales milestones. Additionally, the Company is required to pay a low-single-digit percentage royalty on net sales of products covered by issued patents licensed under the agreements with UWA. Corresponding with the FDA approval of EXONDYS 51 in 2016, the Company recorded a $1.0 million milestone payment as an in-licensed right intangible asset in its consolidated balance sheet. Similarly, corresponding to the milestone payments associated with the FDA approval of VYONDYS 53 in December 2019, the Company recorded a $0.5 million milestone payment as an in-licensed right intangible asset in its consolidated balance sheet. Both intangible assets are being amortized on a straight-line basis over the remaining life of the relevant patents and have a combined carrying value of $1.1 million as of December 31, 2019. For the year ended December 31, 2019, the Company recorded $3.5 million in royalty expense, which is included in cost of sales, related to agreements with UWA with no such an expense incurred in 2018 or 2017. As of December 31, 2019, no other development, regulatory or sales milestones were deemed probable of being achieved and, accordingly, no additional in-licensed rights or expenses have been recognized.

Milestone Obligations

As of December 31, 2019, the Company may be obligated to make up to $3.0 billion of future development, regulatory, commercial, and up-front royalty payments associated with its collaboration and license agreements. For the years ended December 31, 2019, 2018 and 2017, the Company recognized approximately $113.2 million, $142.4 million and $22.0 million relating to certain up-front, milestone and settlement payments as research and development expense, respectively, under these agreements. The Company is also obligated to pay royalties on net sales of certain of its products related to these collaboration and license agreements. The royalty rates range from the low-single-digit to high teens percentages for both inside and outside the U.S.

GAIN FROM SALE OF PRIORITY REVIEW VOUCHER

12 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

GAIN FROM SALE OF PRIORITY REVIEW VOUCHER

4. GAIN FROM SALE OF PRIORITY REVIEW VOUCHER

In March 2017, the Company completed a sale of its Rare Pediatric Disease Priority Review Voucher (“PRV”) to Gilead Sciences, Inc. for $125.0 million, which was recorded as a gain from sale of the PRV as it did not have a carrying value at the time of the sale.

FAIR VALUE MEASUREMENTS

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

FAIR VALUE MEASUREMENTS

5. FAIR VALUE MEASUREMENTS

The tables below present information about the Company’s financial assets that are measured and carried at fair value and indicate the level within the fair value hierarchy of the valuation techniques it utilizes to determine such fair value:

	Fair Value Measurement as of December 31, 2019
	Total		Level 1		Level 2		Level 3
	(in thousands)
Assets
Money market funds	$	203,410	$	203,410	$	—	$	—
Government and government agency bonds		809,159		809,159		—		—
Strategic equity investments		31,937		1,937		—		30,000
Certificates of deposit		1,001		1,001		—		—
Total assets	$	1,045,507	$	1,015,507	$	—	$	30,000

Liabilities
Contingent consideration		5,200		—		—		5,200
Total liabilities	$	5,200	$	—	$	—	$	5,200

	Fair Value Measurement as of December 31, 2018
	Total		Level 1		Level 2		Level 3
	(in thousands)
Assets
Money market funds	$	42,920	$	42,920	$	—	$	—
Commercial paper		125,907		—		125,907		—
Government and government agency bonds		760,235		760,235		—		—
Corporate bonds		43,468		43,468		—		—
Strategic equity investments		31,739		1,739		—		30,000
Certificates of deposit		1,001		1,001		—		—
Total	$	1,005,270	$	849,363	$	125,907	$	30,000

The Company’s assets with fair value categorized as Level 1 within the fair value hierarchy include money market funds, government and government agency bonds, corporate bonds, certificates of deposit, and the Company’s strategic investment in Lysogene, a publicly traded company in France, as more fully described in Note 3, License and Collaboration Agreements. Certain of the government and government agency bonds and corporate bonds are publicly traded fixed income securities and are presented as cash equivalents on the consolidated balance sheets.

The Company’s assets with fair value categorized as Level 2 within the fair value hierarchy consist of commercial paper and government and government agency bonds. These assets have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, through income-based approaches utilizing market observable data.

The Company’s assets with fair value categorized as Level 3 within the fair value hierarchy consists of a strategic investment in Series A preferred stock of Lacerta as more fully described in Note 3, License and Collaboration Agreements. The fair value of the asset was initially based on a cost approach corroborated by the Black-Scholes option pricing model. The most significant assumptions in the option pricing model include historical volatility of similar public companies, estimated term through Lacerta’s potential exit and a risk-free rate based on certain U.S. Treasury rates. At the end of each reporting period, the fair value will be adjusted if Lacerta issues similar or identical equity securities or when there is a triggering event for impairment. There were no changes in the fair value of the Lacerta strategic investment during the year ended December 31, 2019.

The Company’s contingent consideration liability with fair value categorized as Level 3 within the fair value hierarchy relate to the regulatory-related contingent payments to Myonexus selling shareholders as well as to an academic institution under a separate license agreement that meet the definition on a derivative. For more information related to Myonexus, please read Note 3, License and Collaboration Agreements. This amount was estimated through an income approach based on the probability-weighted expected cash flows that incorporated industry-based probability adjusted assumptions relating to the achievement of the milestone and thus the likelihood of making the payments. This fair value measurement was based upon significant inputs not observable in the market and therefore represented a Level 3 measurement. At the end of each reporting period, the fair value is adjusted to reflect the most current assumptions through earnings. There were no changes in the fair value of the contingent consideration during the year ended December 31, 2019. As of December 31, 2019, the contingent consideration was recorded as a non-current liability on the Company’s consolidated balance sheets.

The carrying amounts reported in the consolidated balance sheets for cash and cash equivalents, accounts receivable and accounts payable approximate fair value because of the immediate or short-term maturity of these financial instruments. For fair value information related to the Company’s debt facilities, please read Note 13, Indebtedness.

CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES

12 Months Ended

Dec. 31, 2019

Cash And Cash Equivalents [Abstract]

CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES

6. CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES

The following table summarizes the Company’s financial assets with maturities of equal to or less than three months from the date of purchase included in cash equivalents in the consolidated balance sheets for each of the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Money market funds	$	203,410	$	42,920
Government and government agency bonds		519,491		111,587
Commercial paper		—		14,940
Total	$	722,901	$	169,447

It is the Company’s policy to mitigate credit risk in its financial assets by maintaining a well-diversified portfolio that limits the amount of exposure as to maturity and investment type. The weighted average maturity of the Company’s available-for-sale securities as of December 31, 2019 and 2018 was approximately two months. The following tables summarize the Company’s cash, cash equivalents and investments for each of the periods indicated:

	As of December 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Market Value
	(in thousands)
Cash and money market funds	$	315,589	$	—	$	—		$	315,589
Government and government agency bonds		809,090		71		(2	)		809,159
Total cash, cash equivalents and investments	$	1,124,679	$	71	$	(2	)	$	1,124,748
As reported:
Cash and cash equivalents	$	835,044	$	36	$	—		$	835,080
Short-term investments		289,635		35		(2	)		289,668
Total cash, cash equivalents and investments	$	1,124,679	$	71	$	(2	)	$	1,124,748

	As of December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Market Value
	(in thousands)
Cash and money market funds	$	244,302	$	—	$	—		$	244,302
Commercial paper		125,907		—		—			125,907
Government and government agency bonds		760,258		12		(35	)		760,235
Corporate bonds		43,544		—		(76	)		43,468
Total cash, cash equivalents and investments	$	1,174,011	$	12	$	(111	)	$	1,173,912
As reported:
Cash and cash equivalents	$	370,827	$	3	$	(1	)	$	370,829
Short-term investments		803,184		9		(110	)		803,083
Total cash, cash equivalents and investments	$	1,174,011	$	12	$	(111	)	$	1,173,912

ACCOUNTS RECEIVABLE AND RESERVES FOR PRODUCT SALES

12 Months Ended

Dec. 31, 2019

Receivables Net Current [Abstract]

ACCOUNTS RECEIVABLE AND RESERVES FOR PRODUCT SALES

7. ACCOUNTS RECEIVABLE AND RESERVES FOR PRODUCT SALES

The following table summarizes the components of the Company’s accounts receivable for the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Product sales, net of discounts and allowances	$	90,409	$	48,252
Government contract receivables		470		792
Total accounts receivable, net	$	90,879	$	49,044

The balance for government contract receivables for both periods presented is subject to government audit and will not be collected until the completion of the audit.

The following table summarizes an analysis of the change in reserves for discounts and allowances for the periods indicated:

	Chargebacks			Rebates			Prompt Pay			Other Accruals			Total
	(in thousands)
Balance, as of December 31, 2017	$	995		$	6,959		$	169		$	464		$	8,587
Provision		12,284			28,420			2,624			5,286			48,614
Payments/credits		(11,901	)		(11,103	)		(2,255	)		(3,432	)		(28,691	)
Balance, as of December 31, 2018	$	1,378		$	24,276		$	538		$	2,318		$	28,510
Provision		9,698			44,749			4,897			9,643			68,987
Payments/credits		(10,488	)		(24,287	)		(3,929	)		(7,290	)		(45,994	)
Balance, as of December 31, 2019	$	588		$	44,738		$	1,506		$	4,671		$	51,503

The following table summarizes the total reserves above included in the Company’s consolidated balance sheets for the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Reduction to accounts receivable	$	6,254	$	2,364
Component of accrued expenses		45,249		26,146
Total reserves	$	51,503	$	28,510

INVENTORY

12 Months Ended

Dec. 31, 2019

Inventory Disclosure [Abstract]

INVENTORY

8. INVENTORY

The following table summarizes the components of the Company’s inventory for each of the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Raw materials	$	82,030	$	71,313
Work in progress		88,031		47,279
Finished goods		1,318		6,853
Total inventory	$	171,379	$	125,445

OTHER ASSETS

12 Months Ended

Dec. 31, 2019

Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]

OTHER ASSETS

9. OTHER ASSETS

The following table summarizes the Company’s other current assets for each of the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Manufacturing-related deposits and prepaids	$	54,276	$	39,036
Prepaid clinical and pre-clinical expenses		8,263		9,706
Prepaid maintenance services		4,366		2,994
Leasehold improvement receivable		3,059		13,474
Prepaid insurance		2,573		1,006
Prepaid income tax		2,114		2,130
Prepaid research expenses		2,007		1,932
Other		5,249		7,504
Total other current assets	$	81,907	$	77,782

The following table summarizes the Company’s other non-current assets for each of the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Manufacturing-related deposits and prepaids	$	122,091	$	62,821
Strategic investments		31,937		31,739
Restricted cash and investments		9,566		1,001
Prepaid clinical expenses		4,665		7,541
Alternative minimum tax credit		3,367		3,367
Other		2,233		825
Total other non-current assets	$	173,859	$	107,294

PROPERTY AND EQUIPMENT, NET

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

PROPERTY AND EQUIPMENT, NET

10. PROPERTY AND EQUIPMENT, NET

Property and equipment are recorded at historical cost, net of accumulated depreciation. The following table summarizes components of property and equipment, net for each of the periods indicated:

	As of December 31,
	2019			2018
	(in thousands)
Leasehold improvements	$	53,950		$	20,937
Software and computer equipment		30,683			15,774
Lab equipment		30,053			17,659
Building and improvements		23,108			22,972
Furniture and fixtures		7,090			3,227
Land		5,183			4,158
Land improvements		3,403			—
Office equipment		1,157			436
Construction in progress		25,988			40,010
Property and equipment, gross		180,615			125,173
Less: accumulated depreciation		(50,995	)		(28,149	)
Property and equipment, net	$	129,620		$	97,024

For the years ended December 31, 2019, 2018 and 2017, depreciation expense totaled $22.8 million, $10.2 million and $6.4 million, respectively.

INTANGIBLE ASSETS

12 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

INTANGIBLE ASSETS

11. INTANGIBLE ASSETS

The following table summarizes the components of the Company’s intangible assets for each of the periods indicated:

	As of December 31,
	2019			2018
	(in thousands)
Patents	$	8,902		$	7,227
In-licensed rights		8,073			7,573
Software licenses		1,029			626
Intangible assets, gross		18,004			15,426
Less: accumulated amortization		(5,507	)		(3,852	)
Intangible assets, net	$	12,497		$	11,574

The in-licensed rights relate to agreements with BioMarin and UWA. As a result of the FDA approval of EXONDYS 51 and VYONDYS 53, the Company recorded in-licensed rights of $1.0 million and $0.5 million, respectively. Following the execution of the settlement and license agreements with BioMarin in July 2017, the Company recorded a $6.6 million intangible asset related to EXONDYS 51 in the U.S. The in-licensed rights are being amortized on a straight-line basis over the remaining life of the related patent because the life of the related patent reflects the expected time period that the Company will benefit from the in-licensed right. For more information about the in-licensed rights, please read Note 3, License and Collaboration Agreements. For the years ended December 31, 2019, 2018 and 2017, the Company recorded $0.8 million, $0.9 million and $1.1 million, respectively, of amortization related to the in-license rights.

Patent amortization expense was $0.4 million, $0.7 million and $0.6 million for the years ended December 31, 2019, 2018 and 2017, respectively. Total amortization expense was $1.7 million, $2.1 million and $1.7 million for the years ended December 31, 2019, 2018 and 2017, respectively. The Company also expensed the remaining net book value of previously capitalized patents that were later abandoned of $0.2 million, $0.1 million and $0.6 million for the years ended December 31, 2019, 2018 and 2017, respectively, which were included in research and development expenses on the consolidated statements of operations and comprehensive loss.

Additionally, in 2018, the Company reviewed its patent portfolio and identified technology that the Company will no longer pursue. As a result, the Company impaired these patent assets and recorded $3.8 million in impairment loss for the year ended December 31, 2018, which was included in research and development expense on the consolidated statement of operations and comprehensive loss. There was no such loss recorded in the years ended December 31, 2019 and 2017.

The following table summarizes the estimated future amortization for intangible assets:

	As of December 31, 2019 (in thousands)
2020	$	1,358
2021		1,168
2022		1,156
2023		1,156
2024		1,149
Thereafter		6,510
Total	$	12,497

ACCRUED EXPENSES

12 Months Ended

Dec. 31, 2019

Payables And Accruals [Abstract]

ACCRUED EXPENSES

12. ACCRUED EXPENSES

The following table summarizes the Company’s accrued expenses for each of the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Product revenue related reserves	$	45,249	$	26,146
Accrued employee compensation costs		43,240		24,692
Accrued contract manufacturing costs		27,622		15,794
Accrued milestone expense		18,390		24,020
Accrued clinical and pre-clinical costs		18,010		11,396
Accrued professional fees		10,707		11,319
Accrued collaboration cost-sharing		9,000		2,167
Accrued royalties		6,301		8,254
Other		7,008		10,307
Total accrued expenses	$	185,527	$	134,095

INDEBTEDNESS

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

INDEBTEDNESS

13. INDEBTEDNESS

2024 Convertible Notes

On November 14, 2017, the Company issued $570.0 million senior notes due on November 15, 2024 (the “2024 Notes”). The 2024 Notes were issued at face value and bear interest at the rate of 1.50% per annum, payable semi-annually in cash on each May 15 and November 15, commencing on May 15, 2018. The 2024 Notes contain customary covenants and events of default, occurrence of which will permits the certain holders to accelerate all outstanding obligations, including principal and interest.

Upon conversion, the Company may pay cash, shares of its common stock or a combination of cash and stock, as determined by the Company in its discretion. The 2024 Notes may be convertible into 7,763,552 shares of the Company’s common stock under certain circumstances prior to maturity at a conversion rate of 13.621 shares per $1,000 principal amount of the 2024 Notes, which represents a conversion price of $73.42 per share, subject to adjustment under certain conditions.

The Company allocated the proceeds received from issuance of the 2024 Notes between the liability component and the embedded conversion option, or equity component. The liability component was determined by measuring the fair value of similar notes that do not include the embedded conversion option. The Company allocated $161.1 million to the equity component, which was determined by deducting the fair value of the liability component from the par value of the 2024 Notes. The equity component, net of allocated offering costs of $4.2 million, was recorded as an increase additional paid-in capital. The equity component, plus $10.6 million of offering costs allocated to the liability component, represent the total debt discount on the 2024 Notes at issuance. The debt discount is amortized under the effective interest method and recorded as additional interest expense over the life of the 2024 Notes. The effective interest rate on the liability component of the 2024 Notes for the year ended December 31, 2019, 2018 and 2017 was 6.9%.

Upon the occurrence of a “fundamental change”, which includes (1) change in beneficial ownership of the Company where any person/group possesses more than 50% of the voting power of the Company, (2) consolidation or merger of the Company, (3) shareholder approval of a liquidation plan or (4) the Company is delisted from NYSE or NASDAQ, the holders may require the Company to repurchase all or a portion of the 2024 Notes for cash at 100% of the principal amount of the 2024 Notes being purchased, plus any accrued and unpaid interest. Additionally, upon the occurrence of a “make-whole fundamental change” prior to the maturity date, the Company shall adjust the conversion rate on a sliding scale basis detailed in the agreement

To minimize the impact of potential dilution upon conversion of the 2024 Notes, the Company separately entered into capped call transactions with certain counterparties. The capped calls have a strike price of $73.42 and a cap price of $104.88 and are exercisable when and if the 2024 Notes are converted. If, upon conversion of the 2024 Notes, the price of the Company’s common stock is between the strike price and the cap price of the capped calls, the counterparties will deliver shares of the Company’s common stock and/or cash with an aggregate value equal to the difference between the price of the Company’s common stock at the conversion date and the strike price, multiplied by the number of shares of the Company’s common stock related to the capped calls being exercised. The Company paid $50.9 million for these capped calls transactions, which was recorded as additional paid-in capital.

Term Loans and Revolving Line of Credit

December 2019 Term Loan

On December 13, 2019, the Company entered into a loan agreement (the “Loan Agreement”) which provides a term loan (“December 2019 Term Loan”) of $500.0 million with Biopharma Credit PLC and Biopharma Credit Investments V (Master) LP (collectively, the “Lenders”). The 2019 Term Loan has two tranches: A and B, each of which has a loan amount of $250.0 million. On December 20, 2019, Sarepta drew down tranche A of the 2019 Term Loan and has the option of draw down tranche B of the loan no later than December 31, 2020, subject to certain conditions. The December 2019 Term Loan matures on December 20, 2023, when the principal amount of the loan will become due.

Borrowings under the Loan Agreement bore interest at a rate per annum equal to 8.5%, which shall be payable quarterly in arrears. The Company is also required to pay the Lenders (1) a fee of 1.75% of the amounts drawn under both tranche A and tranche B due on closing (if and when drawn down), (2) a fee of 2.0% of principal amount on the December 2019 Term Loan maturity date or prepayment amount on each prepayment date and (3) certain out-of-pocket expenses incurred by the Lenders.

The Company may voluntarily prepay, in whole or in part, the outstanding balance under the December 2019 Term Loan at any time after the tranche A closing date. Upon occurrence of a change in control, the Company is required to repay any amounts outstanding under the December 2019 Term Loan. In the event of a permitted prepayment, the Company would be obligated to make the following premium payments: (1) an amount equal to the sum of all interest that would have been accrued and payable from the prepayment date through December 20, 2021 (“Makewhole Amount”), and (2) an amount equal to 1.0% to 2.0% of the prepayment amount depending on the date of the prepayment (“Prepayment Premium”).

The Loan Agreement contains customary affirmative and negative covenants as well as events of default, the occurrence of which would permit the Lenders to accelerate the payment of all outstanding obligations, including the payment of the Makewhole Amount and Prepayment Premium.

As of December 31, 2019, the Company recorded a debt discount of $9.4 million and debt issuance costs of $0.7 million, both of which are being treated as deduction to the carrying value of the December 2019 Term Loan and amortized as interest expense over the term of the loan based on an effective interest method. The debt discount of $9.4 million is inclusive of (1) the initial fee of 1.75% payable to the Lenders and (2) the 2.0% fee payable to the Lenders at maturity or prepayment of the December 2019 Term Loan. This amount is recorded within other long-term liabilities in the Company’s consolidated balance sheets. After certain debt discounts and debt issuance costs, the Company received net proceeds of $244.9 million.

July 2017 Term Loan and Revolving Line of Credit

In July 2017, the Company entered into an amended and restated credit agreement (the “Amended and Restated Credit and Security Agreement”) with MidCap Financial Trust (“MidCap”) which provided a term loan of $60.0 million, bearing interest at a rate of 6.25%, plus the one-month London Interbank Offered Rate (“LIBOR”). In addition, in July 2017, the Company entered into a revolving credit and security agreement (the “Revolving Credit Agreement”) with MidCap which provided an aggregate revolving loan commitment of $40.0 million, bearing interest at a rate of 3.95%, plus the one-month LIBOR. In September 2018, the Company terminated both the Amended and Restated Credit and Security Agreement and the Revolving Credit Agreement with MidCap and paid off all amounts due thereunder, including any accrued and unpaid interest. As a result, the Company recorded a debt extinguishment loss of $2.3 million primarily related to the write-off of unamortized debt issuance costs and prepayment fees.

As of December 31, 2019, the Company recorded approximately $681.9 million as long-term debt on the consolidated balance sheets. For the years ended December 31, 2019, 2018 and 2017, the Company recorded $30.7 million, $33.7 million and $5.8 million of interest expense, respectively.

The following table summarizes the Company’s debt facilities for the periods indicated:

	As of December 31,
	2019			2018
	(in thousands)
Principal amount of the 2024 Notes	$	570,000		$	570,000
Unamortized discount - equity component		(120,182	)		(140,206	)
Unamortized discount - debt issuance costs		(7,922	)		(9,240	)
Net carrying value of 2024 Notes		441,896			420,554
Principal amount of the 2019 Term Loan		250,000			—
Unamortized discounts		(9,996	)		—
Net carrying value of 2019 Term Loan		240,004			—
Total carrying value of debt facilities		681,900			420,554
Fair value of 2024 Notes		1,141,288			952,681
Fair value of 2019 Term Loan		250,000			—
Total fair value of debt facilities	$	1,391,288		$	952,681

The fair value of the 2024 Notes is based on open market trades and is classified as level 1 in the fair value hierarchy. The fair value of the December 2019 Term Loan, approximating its principal amount due to the close proximity of the reporting date and the tranche A close date, is classified as level 2 in the fair value hierarchy as it is based on market observable inputs.

The following table summarizes the total gross payments due under the Company’s debt arrangements:

	As of December 31, 2019
	(in thousands)
2020	$	—
2021		—
2022		—
2023		250,000
2024		570,000
Thereafter		—
Total payments	$	820,000

EQUITY

12 Months Ended

Dec. 31, 2019

Equity [Abstract]

EQUITY

14. EQUITY

In March 2019, the Company sold approximately 2.6 million shares of common stock through an underwritten public offering. The offering price was $140.41 per share. The Company received net proceeds of approximately $365.4 million from the offering, net of commission and offering expenses of approximately $0.3 million.

In November 2019, the Company issued approximated 0.3 million shares of common stock with a fair value of $29.4 million as part of the up-front consideration to StrideBio (see Note 3, License and Collaboration Agreements).

In November 2018, the Company sold approximately 4.1 million shares of common stock through an underwritten public offering, including 0.3 million shares sold to the underwriters. The offering price was $131.00 per share. The Company received net proceeds of approximately $513.4 million from the offering, net of commission and offering expenses of approximately $24.6 million.

In July 2017, the Company sold approximately 8.8 million shares of common stock through an underwritten public offering, including 1.2 million shares sold to the underwriters. The offering price was $42.50 per share. The Company received net proceeds of approximately $354.0 million from the offering, net of commission and offering expenses of approximately $20.0 million.

STOCK-BASED COMPENSATION

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

STOCK-BASED COMPENSATION

15. STOCK-BASED COMPENSATION

In June 2011, the Company’s stockholders approved the 2011 Equity Incentive Plan (“2011 Plan”). The 2011 Plan, which as amended authorized 16.0 million shares of common stock to be issued, allowed for the grant of stock options, stock appreciation rights (“SARs”), restricted stock awards (“RSAs”), restricted stock units (“RSUs”), performance shares and performance units. During 2018, the 2011 Plan was merged into the 2018 Plan (defined below). As a result, there were no shares of common stock remaining available for future grant under the 2011 Plan.

In June 2013, the Company’s stockholders approved the 2013 Employee Stock Purchase Plan (“ESPP”) with approximately 0.3 million shares of common stock available to be issued. In June 2016 and 2019, the Company’s stockholders approved additional approximately 0.3 million and 0.5 million shares, respectively, of common stock available to be issued to be added to the 2013 ESPP. As of December 31, 2019, 0.6 million shares of common stock remain available for future grant under the 2013 ESPP.

In September 2014, the Company initiated the 2014 Employment Commencement Incentive Plan (“2014 Plan”) with approximately 0.6 million shares of common stock available to be issued. In October 2015, June 2017 and July 2018, the 2014 Plan was increased by 1.0 million, 3.8 million and 1.2 million shares of common stock available to be issued, respectively. As of December 31, 2019, 0.6 million shares of common stock remain available for future grant under the 2014 Plan.

In June 2018, the Company’s stockholders approved the 2018 Equity Incentive Plan (“2018 Plan”). The 2018 Plan, which authorized 2.9 million shares of common stock to be issued, allows for the grant of stock options, SARs, RSAs, RSUs, performance shares and performance units. The 2011 Plan was merged into the 2018 Plan and, as a result, all remaining shares in the 2011 Plan were transferred into the 2018 Plan. As of December 31, 2019, 3.4 million shares of common stock remain available for future grant under the 2018 Plan.

Stock Options

In general, stock options have a ten-year term and vest over a four-year period, with one-fourth of the underlying shares vesting on the first anniversary of the grant and 1/48th of the underlying shares vesting monthly thereafter, such that the underlying shares will be fully vested on the fourth anniversary of the grant, subject to the terms of the applicable plan under which they were granted.

The fair values of stock options granted during the periods presented are measured on the date of grant using the Black-Scholes-Merton option-pricing model, with the following assumptions:

	For the Year Ended December 31,
	2019	2018	2017
Risk-free interest rate (1)	1.4 - 2.5%	2.5 - 3.0%	1.6 - 2.1%
Expected dividend yield (2)	—	—	—
Expected term (3)	5.04 years	5.06 years	4.2 - 4.8 years
Expected volatility (4)	52.5 - 68.9%	52.4 - 60.8%	54.0 - 63.0%

(1)	The risk-free interest rate is estimated using an average of Treasury bill interest rates over a historical period commensurate with the expected term of the option that correlates to the prevailing interest rates at the time of grant.

(2)	The expected dividend yield is zero as the Company has not paid any dividends to date and does not expect to pay dividends in the future.

(3)	The expected term is estimated using historical exercise behavior.

(4)	The expected volatility is the implied volatility in exchange-traded options of the Company’s common stock.

The amounts estimated according to the Black-Scholes-Merton option-pricing model may not be indicative of the actual values realized upon the exercise of these options by the holders.

The following tables summarize the Company’s stock option activity for each of the periods indicated:

	For the Year Ended December 31,
	2019					2018					2017
				Weighted					Weighted						Weighted
				Average					Average						Average
				Exercise					Exercise						Exercise
	Shares			Price		Shares			Price		Shares				Price
Grants outstanding at beginning of the period		8,391,171		$	46.09		8,806,204		$	29.74		5,436,951			$	22.70
Granted		1,429,652			132.97		2,152,439			90.15		4,805,722		(1)		35.09
Exercised		(1,055,715	)		30.73		(2,119,306	)		22.89		(792,845	)			17.40
Expired and forfeited		(418,760	)		84.15		(448,166	)		46.11		(643,624	)			25.44
Grants outstanding at end of the period		8,346,348		$	61.01		8,391,171		$	46.09		8,806,204			$	29.74

Grants exercisable at end of the period		2,368,621		$	45.33		2,304,791		$	27.69		3,288,712			$	24.76
Grants vested and expected to vest at end of the period		7,987,427		$	58.65		6,643,835		$	45.43		6,910,022			$	28.49

(1)	Includes 3,300,000 options with service and market conditions granted to the Company’s CEO. These options have a five-year cliff vesting schedule. The fair value of $13.48 for these options was determined by a lattice model with Monte Carlo simulations.

The weighted-average grant date fair value per share of stock options granted during the years ended December 31, 2019, 2018 and 2017 was $70.93, $44.66 and $14.78, respectively.

			Weighted
	Aggregate		Average
	Intrinsic		Remaining
	Value		Contractual
	(in thousands)		Life (Years)
Options outstanding at December 31, 2019	$	587,191	7.5
Options exercisable at December 31, 2019	$	199,438		6.0
Options vested and expected to vest at December 31, 2019	$	578,938	7.4

The following table summarizes the Company’s stock options vested and exercised for each of the periods indicated:

	For the Year Ended December 31,
	2019		2018		2017
	(in thousands)
Aggregate grant date fair value of stock options vested	$	50,878	$	16,316	$	18,225
Aggregate intrinsic value of stock options exercised	$	109,707	$	158,936	$	20,922

For the years ended December 31, 2019, 2018 and 2017, the Company has recognized approximately $0.1 million, $0.2 million and $0.9 million in stock-based compensation expense related to the options with performance-based criteria, respectively.

Restricted Stock Awards

The Company grants RSAs to members of its board of directors and certain employees. The following table summarizes the Company’s RSA activity for each of the periods indicated:

	For the Year Ended December 31,
	2019					2018					2017
				Weighted					Weighted					Weighted
				Average					Average					Average
				Grant Date					Grant Date					Grant Date
	Shares			Fair Value		Shares			Fair Value		Shares			Fair Value
Grants outstanding at beginning of the period		252,321		$	42.37		411,781		$	37.23		153,170		$	34.53
Granted		—			—		27,590			98.57		341,500			34.58
Vested		(100,840	)		40.54		(187,050	)		39.34		(63,264	)		14.60
Cancelled		(15,356	)		48.94		—			—		(19,625	)		43.02
Grants outstanding at end of the period		136,125		$	42.98		252,321		$	42.37		411,781		$	37.23

In September 2016, the Company granted certain executives RSAs with a performance conditions relating to certain sales targets. If the sales targets are achieved within the required time frame, the number of RSAs may be increased from 71,925 to 89,906 shares. In December 2017, the Company modified the expiration date of these RSAs from June 30, 2018 to January 1, 2019. As a result of this modification, the fair value per RSA was changed from $48.94 to $54.29. Through December 31, 2017, the Company had not recorded any stock-based compensation expense associated with these awards as the achievement of the performance conditions was not deemed probable. As of December 31, 2018, the first sales target related to these RSAs was achieved and, accordingly, the Company recognized approximately $3.3 million of stock-based compensation expense during the year ended December 31, 2018. The second target was not achieved and the shares related to this target were subsequently cancelled and no expense was recognized.

Restricted Stock Units

The Company also grants RSUs to members of its board of directors and employees. The following table summarizes the Company’s RSU activity for the periods indicated:

	For the Year Ended December 31,
	2019					2018					2017
				Weighted					Weighted					Weighted
				Average					Average					Average
				Grant Date					Grant Date					Grant Date
	Shares			Fair Value		Shares			Fair Value		Shares			Fair Value
Grants outstanding at beginning of the period		251,298		$	81.21		66,552		$	33.72		—		$	—
Granted		511,283			131.18		230,736			87.95		181,029			33.03
Vested		(84,068	)		75.12		(30,276	)		33.23		(78,017	)		32.63
Cancelled		(72,639	)		103.03		(15,714	)		71.45		(36,460	)		32.63
Grants outstanding at end of the period		605,874		$	121.61		251,298		$	81.21		66,552		$	33.72

In March 2017, the Company granted certain executives 156,029 RSUs with performance conditions relating to certain sales target and regulatory milestones, which were achieved between June 2017 and March 2019. As of December 31, 2019, there were no RSUs with performance conditions remaining to be vested. For the years ended December 31, 2019, 2018 and 2017, the Company recognized approximately $0.5 million, $0.2 million and $2.9 million of stock-based compensation expense, respectively.

Stock Appreciation Rights

The Company issues SARs on the same terms as options granted to employees. The grant date fair value of the SARs is determined using the same valuation assumptions as for stock options described above. Stock-based compensation expense is recognized on a straight-line basis over the vesting period of the SARs.

The following table summarizes the Company’s SAR activity for each of the periods indicated:

	For the Year Ended December 31,
	2019						2018				2017
				Weighted					Weighted				Weighted
				Average					Average				Average
				Exercise					Exercise				Exercise
	Shares			Price			Shares		Price		Shares		Price
Grants outstanding at beginning of the period		100,000		$	23.85			100,000	$	23.85		100,000	$	23.85
Exercised		(100,000	)	$	(23.85	)		—	$	—		—	$	—
Grants outstanding at end of the period		—		$	—			100,000	$	23.85		100,000	$	23.85
Grants exercisable at end of the period		—		$	—			100,000	$	23.85		100,000	$	23.85
Grants vested and expected to vest at end of the period		—		$	—			100,000	$	23.85		100,000	$	23.85

2013 Employee Stock Purchase Plan

Under the Company’s 2013 ESPP, participating employees purchase common stock through payroll deductions. The purchase price is equal to 85% of the lower of the closing price of the Company’s common stock on the first business day and the last business day of the relevant purchase period. The 24-month offering period will end between February 29, 2020 and August 31, 2021. The following table summarizes the Company’s ESPP activity for each of the periods indicated:

	For the Year Ended December 31,
	2019		2018		2017
Number of shares purchased		92,086		75,094		102,698
Proceeds received (in millions)	$	5.1	$	2.3	$	1.4

Stock-based Compensation Expense

For the years ended December 31, 2019, 2018 and 2017, total stock-based compensation expense was $78.6 million, $50.1 million and $30.5 million, respectively. Included in the amounts for the year ended December 31, 2017 is $2.1 million of stock-based compensation expense incurred in connection with the resignation of the Company’s former CEO.

The following table summarizes stock-based compensation expense by function included within the consolidated statements of operations and comprehensive loss:

	For the Year Ended December 31,
	2019		2018		2017
	(in thousands)
Research and development	$	27,681	$	14,214	$	8,542
Selling, general and administrative		50,921		35,913		21,923
Total stock-based compensation	$	78,602	$	50,127	$	30,465

The following table summarizes stock-based compensation expense by grant type included within the consolidated statements of operations and comprehensive loss:

	For the Year Ended December 31,
	2019		2018		2017
	(in thousands)
Stock options	$	53,427	$	37,671	$	23,416
Restricted stock awards/units		20,103		10,632		5,295
Employee stock purchase plan		5,072		1,824		1,754
Total stock-based compensation	$	78,602	$	50,127	$	30,465

As of December 31, 2019, there was $181.1 million of total unrecognized stock-based compensation expense related to the Company’s stock-based compensation plans. The expense is expected to be recognized over a weighted-average period of approximately 3 years. Of this amount, $109.5 million relates to options with service conditions only, $22.1 million relates to awards with service and market conditions, less than $0.1 million relates to awards with performance conditions, and the remaining $49.5 million related to restricted stock awards or restricted stock units with service conditions only.

401 (K) PLAN

12 Months Ended

Dec. 31, 2019

Compensation And Retirement Disclosure [Abstract]

401 (K) PLAN

16. 401 (K) PLAN

The Company sponsors a 401(k) Plan (“the Plan”) in the U.S. and other retirement plans in the rest of the world, all of which are defined contribution plans. The Plan is available to all employees who are age 21 or older. Participants may make voluntary contributions and the Company makes matching contributions according to the Plan’s matching formula. Matching contributions fully vest after one year of service for all employees. The expense related to the Plan primarily consists of the Company’s matching contributions.

Expense related to the Plan totaled $3.4 million, $2.1 million and $1.4 million for the years ended December 31, 2019, 2018 and 2017, respectively.

OTHER (LOSS) INCOME

12 Months Ended

Dec. 31, 2019

Other Income And Expenses [Abstract]

OTHER (LOSS) INCOME

17. OTHER (LOSS) INCOME

The following table summarizes other income and loss for the periods indicated:

	For the Year Ended December 31,
	2019			2018			2017
	(in thousands)
Interest expense	$	(30,669	)	$	(33,709	)	$	(5,801	)
Interest income		7,238			6,810			1,809
Amortization of investment discount		15,350			8,573			1,401
Other expense		(236	)		(656	)		601
Gain from sale of Priority Review Voucher		—			—			125,000
Total other (loss) income	$	(8,317	)	$	(18,982	)	$	123,010

INCOME TAXES

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

INCOME TAXES

18. INCOME TAXES

The following table summarizes the loss before the provision for income taxes by jurisdiction for the periods indicated:

	For the Year Ended December 31,
	2019			2018			2017
	(in thousands)
Domestic	$	(489,747	)	$	(309,294	)	$	(45,686	)
Foreign		(224,133	)		(53,316	)		(2,942	)
Total	$	(713,880	)	$	(362,610	)	$	(48,628	)

The following table summarizes provision for income taxes in the accompanying consolidated financial statements for the periods indicated:

	For the Year Ended December 31,
	2019			2018			2017
	(in thousands)
Current provision:
Federal	$	—		$	(110	)	$	204
State		521			(653	)		1,856
Foreign		1,050			311			—
Total current provision		1,571			(452	)		2,060
Deferred benefit:
Federal		(15	)		—			—
State		(5	)		—			—
Foreign		(356	)		(240	)		—
Total deferred benefit		(376	)		(240	)		—
Total current provision	$	1,195		$	(692	)	$	2,060

The following table summarizes the reconciliation between the Company’s effective tax rate and the income tax rate for each of the periods indicated:

	For the Year Ended December 31,
	2019				2018				2017
Federal income tax rate		21.0		%		21.0		%		34.0		%
State taxes		6.3				12.3				(27.7	)
Research and development and other tax credits		3.3				3.1				8.5
Valuation allowance		(16.8	)			(45.5	)			(93.2	)
Permanent differences		1.8				6.9				6.4
Sarepta International C.V. return to provision		—				(0.1	)			62.1
Impact of tax reform, net of valuation allowance		—				—				5.9
Basis difference in subsidiary		(8.4	)			—				—
Foreign rate differential		(7.4	)			(0.9	)			(0.6	)
Other		—				3.4				0.4
Effective tax rate		(0.2	)	%		0.2		%		(4.2	)	%

Permanent differences affecting the Company’s effective tax rate primarily include excess stock-based compensation tax deductions, net of non-deductible stock-based compensation and limitation on officer compensation deduction.

In February 2019, the Company exercised its option to acquire Myonexus. Accumulated costs of $253.7 million, associated with the Myonexus acquisition, were expensed for U.S. GAAP purposes. Of the $253.7 million in accumulated costs, $85.0 million relates to up-front and milestone payments as a result of the execution of the Warrant Agreement in May 2018 as well as certain development milestones being achieved or becoming probable of being achieved and $168.7 million relates to the exercise of the exclusive option to acquire Myonexus in February 2019. For U.S. income tax purposes, these costs are considered to be an outside investment in the subsidiary and are not currently deductible for tax purposes. The permanent difference related to this acquisition is separately stated in the rate reconciliation above.

In December 2012, the Company licensed certain intellectual property of Sarepta Therapeutics, Inc. to its wholly owned Netherlands subsidiary, Sarepta International C.V. The parties also entered into a contract research agreement under which Sarepta Therapeutics, Inc. performs research services for Sarepta International C.V. In January 2016, Sarepta Therapeutics, Inc. entered into a manufacturing and distribution agreement as well as service agreement with Sarepta International C.V. In conjunction with its recent filings, it was determined that beginning in 2016, Sarepta International C.V. is effectively connected with the conduct of a trade or business by the entity in the U.S. and, accordingly, the 2016, 2017 and 2018 losses are subject to U.S. income taxes. In May 2018, Sarepta International C.V. merged into another wholly owned U.S. subsidiary of Sarepta Therapeutics, Inc.

The following table summarizes the analysis of the deferred tax assets and liabilities for each of the periods indicated:

	As of December 31,
	2019			2018
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	304,033		$	212,342
Difference in depreciation and amortization		40,095			55,162
Research and development tax credits		103,806			67,309
Stock-based compensation		24,114			15,538
Lease liabilities		15,796			4,831
Deferred revenue		939			888
Capitalized inventory		18,255			22,943
Other		16,270			15,727
Total deferred tax assets		523,308			394,740
Deferred tax liabilities:
Right of use asset		(10,782	)		—
Debt discount		(23,099	)		(25,162	)
Total deferred tax liabilities		(33,881	)		(25,162	)
Valuation allowance		(488,829	)		(369,345	)
Net deferred tax assets	$	598		$	233

The Company has evaluated the positive and negative evidence bearing upon the realizability of its U.S. net deferred tax assets, which are comprised principally of federal and state net operating loss carryforwards, research and development tax credit carryforwards, stock-based compensation expense, capitalized inventory, and intangibles. Under the applicable accounting standards, management has considered the Company’s history of losses and concluded that it is more likely than not that the Company will not recognize the benefits of net federal and state deferred tax assets. Accordingly, a full valuation allowance of the U.S. net deferred tax asset had been established at December 31, 2019 and 2018. The net change in the valuation allowance for deferred tax assets was an increase of $119.5 million and $164.8 million for the years ended December 31, 2019 and 2018, respectively. This increase for the year ended December 31, 2019 was primarily due to the generation of federal and state net operating losses and income tax credits.

The Company generated foreign deferred tax assets mainly consisting of net operating loss carryforwards, stock-based compensation and unrealized gain/losses. Based upon the income projections in the majority of the foreign jurisdictions, the Company believes it will realize the benefit of its future deductible differences in these jurisdictions. As such, the Company has not recorded a valuation allowance against these foreign jurisdictions. Brazil, the Netherlands, Czech Republic, and Spain have generated deferred tax assets, which consist of net operating loss carryforwards and stock-based compensation expense. The Company has concluded that it is more likely than not that we will not recognize the future benefits of the deferred tax assets, and accordingly, a full valuation allowance has been recorded against these foreign deferred tax assets. In 2019, the Company undertook an internal restructuring involving its subsidiary in Switzerland. The restructuring resulted in the utilization of all of its net operating loss carryforwards and the release of its previously established valuation allowance of $7.9 million.

As of December 31, 2019, the Company had federal and state net operating loss carryforwards of $1,166.2 million and $859.0 million, respectively, available to reduce future taxable income. The federal and state net operating loss carry forwards of $579.9 million and $807.7 million will expire at various dates between 2020 and 2039. The federal and state net operating loss carry forwards of $586.3 million and $51.3 million, respectively, can be carried forward indefinitely. Utilization of these net operating losses could be limited under Section 382 of the Internal Revenue Code and similar state laws based on ownership changes and the value of the Company’s stock. Additionally, the Company has $74.7 million and $34.1 million of federal and state research and development credits, respectively, available to offset future taxable income. These federal and state research and development credits begin to expire between 2020 and 2039 and between 2020 and 2034, respectively. The Company also has foreign net operating loss carryforwards of $8.0 million, mainly derived from the net operating loss generated by its subsidiary in Brazil, which may be carried forward indefinitely.

The Company or one of its subsidiaries files income tax returns in the U.S., and various state and foreign jurisdictions. The federal, state and foreign income tax returns are generally subject to tax examinations for the tax years ended December 31, 2016 through December 31, 2018. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service, state or foreign tax authorities to the extent utilized in a future period.

The follow table summarizes the reconciliation of the beginning and ending amount of total unrecognized tax benefits for each of the periods indicated:

	For the Year Ended December 31,
	2019			2018		2017
	(in thousands)
Balance at beginning of the period	$	37,544		$	5,134	$	4,644
Increase related to current year tax positions		4,275			2,164		735
Increase related to prior year tax positions		109			30,246		—
Decrease related to prior year tax positions		(175	)		—		(245	)
Balance at end of the period	$	41,753		$	37,544	$	5,134

The balance of total unrecognized tax benefits at December 31, 2019, if recognized, would not affect the effective tax rate on income from continuing operations, due to a full valuation allowance against the Company’s U.S. deferred tax assets. The Company does not expect that the amount of unrecognized tax benefits to change significantly in the next twelve months. The Company’s policy is to recognize interest and/or penalties related to income tax matters in income tax expense. It had no accrual for interest or penalties on its balance sheet at December 31, 2019 or 2018. No interest and/or penalties were recognized in 2018 or 2017.

LEASES

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

LEASES

19. LEASES

The adoption of ASC 842 resulted in the recognition of operating lease liabilities and ROU assets of $60.1 million and $42.5 million, respectively, on the Company’s balance sheet relating to its leases for its corporate headquarters and its office and lab space on the January 1, 2019 transition date. Further, the Company reclassified upon adoption $18.0 million of deferred rent which reduced the ROU assets recognized on the balance sheet, in accordance with the transition guidance.

As of December 31, 2019, operating lease assets were $37.9 million and operating lease liabilities were $55.6 million. Amounts related to financing leases were immaterial. The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the year ended December 31, 2019:

	For the Year Ended December 31, 2019
	(in thousands)
Lease cost
Operating lease cost	$	10,335
Variable lease cost		3,967
Total lease cost	$	14,302

Other information
Operating lease payments		10,416
Operating lease liabilities arising from obtaining ROU assets		—
Weighted average remaining lease term	5.5
Weighted average discount rate		7.50	%

The following table summarizes maturities of lease liabilities and the reconciliation of lease liabilities as of December 31, 2019:

	As of December 31, 2019
	(in thousands)
2020	$	11,718
2021		12,891
2022		11,080
2023		11,230
2024		11,471
Thereafter		9,654
Total minimum lease payments		68,044
Less: imputed interest		(12,478	)
Total operating lease liabilities	$	55,566
Included in the condensed consolidated balance sheet:
Current portion of lease liabilities within other current liabilities	$	7,846
Lease liabilities		47,720
Total operating lease liabilities	$	55,566

For comparable purposes, aggregate future minimum non-cancellable commitments under leases as of December 31, 2018, are as follows:

	As of December 31, 2018
	(in thousands)
2020	$	11,395
2021		12,558
2022		10,757
2023		10,898
2024		11,128
Thereafter		9,396
Total minimum lease payments	$	66,132

Excluded from the table above are obligations under manufacturing agreements with Brammer Bio MA, LLC (“Brammer”) and Paragon Bioservices, Inc. (“Paragon”). The Company has determined that both agreements contain an embedded lease. However, both leases have not yet commenced as of December 31, 2019, and as such, right of use assets and lease liabilities have not yet been recognized on the Company’s consolidated balance sheets. Refer to Note 21, Commitments and Contingencies for additional details relating to these two agreements.

NET LOSS PER SHARE

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

NET LOSS PER SHARE

20. NET LOSS PER SHARE

Basic net loss per share is computed by dividing net loss by the weighted-average number of shares of common stock outstanding. Diluted net loss per share is computed by dividing net loss by the weighted-average number of shares of common stock and dilutive common stock equivalents outstanding. Given that the Company recorded a net loss for each of the periods presented, there is no difference between basic and diluted net loss per share since the effect of common stock equivalents would be anti-dilutive and are, therefore, excluded from the diluted net loss per share calculation.

	For the Year Ended December 31,
	2019			2018			2017
	(in thousands, except per share amounts)
Net loss	$	(715,075	)	$	(361,918	)	$	(50,688	)
Weighted-average common shares outstanding - basic		73,615			66,250			58,818
Effect of dilutive securities*		—			—			—
Weighted-average common shares outstanding - diluted		73,615			66,250			58,818
Net loss per share — basic and diluted	$	(9.71	)	$	(5.46	)	$	(0.86	)

For the years ended December 31, 2019, 2018 and 2017, stock options, RSAs, RSUs, SARs and ESPP to purchase approximately 9.1 million, 9.1 million and 9.4 million shares of common stock, respectively, were excluded from the net loss per share calculation as their effect would have been anti-dilutive. The Company accounts for the effect of the 2024 Notes on diluted net earnings per share using the if-converted method as they may be settled in cash or shares at the Company’s option. While the closing price on December 31, 2019 exceeded the conversion price of $73.42, the potential shares issuable under the 2024 Notes were excluded from the calculation of diluted loss per share as they were anti-dilutive using the if-converted method. In the period of conversion, the 2024 Notes will have no impact on diluted net loss if they are settled in cash and will have an impact on diluted earnings per share if the 2024 Notes are settled in shares upon conversion and when the Company is in an income position.

COMMITMENTS AND CONTINGENCIES

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

COMMITMENTS AND CONTINGENCIES

21. COMMITMENTS AND CONTINGENCIES

Manufacturing Obligations

The Company has entered into long-term contractual arrangements from time to time for the provision of goods and services.

Brammer Bio MA, LLC

The Company entered into a Development, Commercial Manufacturing and Supply Agreement (the “Brammer Manufacturing Agreement”) and, subsequently, entered into the first amendment (the “Amendment”) to the Brammer Manufacturing Agreement with Brammer in June 2018 and May 2019, respectively (collectively, “Brammer Supply Agreements”). Pursuant to the terms of the Brammer Supply Agreements, Brammer agreed to provide the Company with access to clinical and commercial manufacturing capacity for its gene therapy programs.

Under the Brammer Manufacturing Agreement, the Company will purchase product in batches from Brammer, subject to minimum and maximum annual purchase requirements. Further, the Company: (i) was required to make a $20.0 million advance payment to Brammer upon execution of the agreement in June 2018, (ii) was required to make two non-refundable payments of $5.0 million each to Brammer in the third and fourth quarter of 2018 to be used in the specification, selection, and procurement of the related process equipment to be utilized under the agreement, and (iii) was required to make a $10.0 million quarterly capacity access fee payment to Brammer throughout the term of the agreement.

As a result of the Amendment: (i) the Company now has access to substantially all of the related facility’s capacity, subject to certain minimum and maximum volume limitations, (ii) the Company was required to make a $6.0 million advance payment to Brammer upon execution of the Amendment, and (iii) the quarterly capacity access fee payments due to Brammer throughout the term of the agreement increased from $10.0 million to $13.3 million, starting January 1, 2020. However, through December 31, 2019, a reduced quarterly capacity access fee was in effect as Brammer worked towards achieving full capacity at its facility. In addition, the application of the advance payments will reduce the quarterly capacity access fees paid through 2021.

The term of the Brammer Supply Agreements will continue for a period of six years following the first regulatory approval of a product manufactured under the agreements. The term will automatically renew for successive two years unless the Company notifies Brammer of its intention not to renew (no less than twenty-four months prior to the expiration of the term). The Company also has the ability to terminate the agreement prior to expiration but would be required to continue remitting capacity access fees to Brammer for up to eight additional quarters.

Upon execution of the Amendment, the Company determined that the Brammer Supply Agreements contain an embedded lease because the Company now has the right to direct the use of the facility and related equipment therein. Further, the Company determined that it did not control the facility or related equipment during construction and, thus, the lease did not fall in the scope of “build-to-suit” accounting. The lease has not commenced as of December 31, 2019 because of the clean room suites at the Brammer facility are not yet available for use by the Company. Accordingly, total cumulative payments made to Brammer of $75.5 million have been recorded as an other non-current asset in the accompanying consolidated balance sheets and will be considered in the initial measurement of the cost of the right-of-use asset at the lease commencement date. This amount, along with any additional quarterly access fees payable prior to the lease commencement date, will be amortized on a straight-line basis as rent expense over the term of the embedded lease, beginning on the lease commencement date, currently anticipated to occur during the first half of 2020. Rent expense recognized prior to regulatory approval of the related product will be classified to research and development expense. Upon regulatory approval, rent expense will be classified to cost of inventory with the recognition in cost of sales as the sales of product occur.

Paragon Bioservices, Inc.

The Company entered into a manufacturing collaboration agreement (the “Paragon Collaboration Agreement”) and, subsequently, entered into a manufacturing and supply agreement (the “Paragon Supply Agreement”) with Paragon in October 2018 and February 2019, respectively (collectively, the “Paragon Agreements”). Pursuant to the terms of the Paragon Agreements, Paragon agreed to provide the Company with two dedicated clean room suites and an option to reserve two additional clean room suites for its gene therapy programs. In September 2019, the Company exercised the option to gain access to the additional clean room suites. The Paragon Agreements will expire on December 31, 2024. The Company has the ability to terminate the Paragon Agreements prior to expiration, subject to potential additional financial consideration.

Under the Paragon Agreements, the Company will purchase product in batches from Paragon subject to minimum annual purchase requirements during two periods: the pre-launch period and the post-launch period. During the pre-launch period, the Company is obligated to purchase a minimum amount of $4.0 million of services per quarter per clean room. During the post-launch period, on an annual basis, the Company is obligated to purchase a minimum number of batches per clean room. Further, the Company is required to pay Paragon: (i) use fees of $1.0 million per year per clean room suite after the clean rooms are fully qualified and validated to manufacture the Company’s materials, and (ii) clean room reservation fees totaling $48.0 million. Additional use fees and reservation fees are required if the Company has equipment needs beyond the basic equipment package included in the initial clean room suites. In addition, Paragon will provide the Company with a credit of up to 100% of the clean room use fee if certain clean room capacity utilization thresholds are met.

The Company has concluded that the Paragon Agreements contain an embedded lease as the Company has the right to direct the use of the facility and related equipment therein. The Company also determined that it did not control the facility or related equipment during construction and, thus, the lease did not fall in the scope of “build-to-suit” accounting. The lease has not commenced as of December 31, 2019 because the clean room suites at the Paragon facility are not yet available for use by the Company. Accordingly, cumulative payments totaling $40.1 million made to Paragon have been recorded as an other non-current asset in the accompanying consolidated balance sheets and will be considered in the initial measurement of the cost of the right-of-use asset at the lease commencement date. This amount, along with any additional payments made prior to the lease commencement date, will be amortized on a straight-line basis as rent expense over the term of the embedded lease, beginning on the lease commencement date, currently anticipated to occur in the first quarter of 2020. Use fees associated with the clean room suites are considered contingent rental payments and will be charged to rent expense when (and if) incurred. Rent expense recognized prior to regulatory approval of the related product will be classified to research and development expense. Upon regulatory approval, rent expense will be classified to cost of inventory with the recognition in cost of sales as the sales of product occur.

Aldevron, LLC

In December 2018, the Company entered into a Clinical and Commercial Supply Agreement (the “CCSA”) with Aldevron LLC (“Aldevron”) for the supply of plasmid DNA to fulfill its needs for gene therapy clinical trials and commercial supply. Pursuant to the terms of the CCSA, Aldevron agreed to reserve a certain number of manufacturing slots (“Reserved Slots”) on a quarterly basis. The initial term of the CCSA expired on December 31, 2019. The Company exercised the option to extend the CCSA to December 31, 2020 (the “2020 Option”) and has another option to extend the term of the CCSA for an additional year to December 31, 2021 (the “2021 Renewal Right”).

The Company may be required to make an additional $20.0 million in prepayments associated with the CCSA should the Company exercise the 2021 Renewal Right. The prepayments will be credited back to Sarepta, until exhausted, for each batch of product delivered by Aldevron, in an amount equal to 50% of the batch invoice amount. The Company has determined that the CCSA does not contain an embedded lease because it does not convey the right to control the use of Aldevron’s facility or related equipment therein. As of December 31, 2019, the Company recorded $22.8 million in other current assets in the accompanying balance sheets related to the prepayments made to Aldevron under the CCSA. The gross cost of batches purchased from Aldevron since inception of the agreement have been classified as research and development expense. In the event the Company does not expect services under the CCSA to be rendered to fully exhaust any prepayments made to Aldevron, the applicable balance will be charged to expense at the time this determination is made.

The following table presents non-cancelable contractual obligations arising from long-term contractual arrangements:

	As of December 31, 2019 (in thousands)
2020	$	378,744
2021		183,661
2022		64,653
2023		58,319
2024		58,309
Thereafter		149,350
Total manufacturing commitments	$	893,036

Additionally, should the Company obtain regulatory approval for any drug product candidate produced as a part of the Company’s manufacturing obligations above, additional minimum batch requirements with the respective manufacturing parties would be required.

Other Funding Commitments

The Company has several on-going clinical trials in various clinical trial stages. Its most significant clinical trial expenditures are to contract research organizations (“CROs”). The CRO contracts are generally cancellable at the Company’s option. As of December 31, 2019, the Company has approximately $91.4 million in cancellable future commitments based on existing CRO contracts. For the years ended December 31, 2019, 2018 and 2017, the Company recognized approximately $31.6 million, $19.6 million and $13.9 million, respectively, for expenditures incurred by CROs.

Litigation

In the normal course of business, the Company may from time to time be named as a party to various legal claims, actions and complaints, including matters involving securities, employment, intellectual property, effects from the use of therapeutics utilizing its technology, or others. For example, on August 30, 2019, Plaintiff Andrew Salinger filed a putative class action complaint against the Company and two of its current officers, Douglas S. Ingram and Sandesh Mahatme (collectively, the “Defendants”), in the United States District Court for the Southern District of New York. The complaint alleges that the Defendants violated Section 10(b) of the Securities Exchange Act of 1934, as amended (“Exchange Act”), and Rule 10b-5 promulgated thereunder, as well as Section 20(a) of the Exchange Act, in connection with the Company’s disclosures related to golodirsen. The proposed class consists of all persons or entities who acquired Company securities between September 6, 2017 and August 19, 2019. On December 17, 2019, the district court appointed Bernard Portnoy as lead plaintiff, and set a briefing schedule requiring the amended complaint to be filed on February 18, 2020 and requiring Defendants to answer or otherwise respond to the amended complaint on April 17, 2020. Defendants’ motion to transfer the case to the United States District Court for the District of Massachusetts is pending. On February 14, 2020, the lead plaintiff filed a Notice of Voluntary Dismissal of his claims against all Defendants and the clerk referred the Notice to the court for review and approval. The court has taken no further action. The Company is unable to provide an estimate of possible loss or range of possible loss.

On January 7, 2020, Plaintiff Al Lutzker filed a stockholder derivative complaint, purportedly on behalf of the Company, against two of the Company’s current officers, Douglas S. Ingram and Sandesh Mahatme, and six current members of Company’s Board of Directors, M. Kathleen Behrens, Richard J. Barry, Michael W. Bonney, Mary Ann Gray, Claude Nicaise, and Hans Wigzell (collectively, the “Defendants”), in the United States District Court for the District of Delaware. The complaint asserts claims for breach of fiduciary duty, insider selling, unjust enrichment, waste of corporate assets, and violations of Section 14(a) of the Securities Exchange Act of 1934, and Rule 14a-9 promulgated thereunder, in connection with the Company’s disclosures related to golodirsen. The Company is unable to provide an estimate of possible loss or range of possible loss.

SUBSEQUENT EVENT

12 Months Ended

Dec. 31, 2019

Subsequent Events [Abstract]

SUBSEQUENT EVENT

22. SUBSEQUENT EVENT

On February 14, 2020, the Company entered into an agreement to sell the rare pediatric disease PRV it received from the FDA in connection with the approval of VYONDYS 53 for consideration of $111.0 million. The closing of the transaction is subject to the expiration or termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 and other customary conditions. When the transaction closes, the net proceeds will be recorded as a gain from sale of the PRV as it does not have a carrying value at the time of the sale.

The Company has evaluated subsequent events from the date of the consolidated balance sheet through the date the consolidated financial statements were issued.

FINANCIAL INFORMATION BY QUARTER (UNAUDITED)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

FINANCIAL INFORMATION BY QUARTER (UNAUDITED)

23. FINANCIAL INFORMATION BY QUARTER (UNAUDITED)

	2019 for Quarter Ended
	December 31			September 30			June 30			March 31
	(in thousands)
Revenues:
Product, net	$	100,113		$	99,041		$	94,668		$	87,011
Total revenues		100,113			99,041			94,668			87,011

Cost and expenses:
Cost of sales (excluding amortization of in-licensed rights)		15,567			13,037			15,919			12,063
Research and development		223,141			133,949			113,266			90,553
Selling, general and administrative		81,424			75,429			67,393			60,566
Acquired in-process research and development		—			—			173,240			—
Settlement and license charges		10,000			—			—			—
Amortization of in-licensed rights		200			216			217			216
Total cost and operating expenses		330,332			222,631			370,035			163,398
Operating loss		(230,219	)		(123,590	)		(275,367	)		(76,387	)
Other loss:
Other expense, net		(4,773	)		(2,510	)		(862	)		(172	)
Other loss		(4,773	)		(2,510	)		(862	)		(172	)
Loss before income tax expense		(234,992	)		(126,100	)		(276,229	)		(76,559	)
Income tax expense		711			226			174			84
Net loss	$	(235,703	)	$	(126,326	)	$	(276,403	)	$	(76,643	)

Net loss per share - basic and diluted	$	(3.16	)	$	(1.70	)	$	(3.74	)	$	(1.07	)

Weighted average number of shares of common stock used in computing basic and diluted net loss per share		74,557			74,177			73,958			71,731

	2018 for Quarter Ended
	December 31			September 30			June 30			March 31
	(in thousands)
Revenues:
Product, net	$	84,415		$	78,486		$	73,529		$	64,604
Total revenues		84,415			78,486			73,529			64,604

Cost and expenses:
Cost of sales (excluding amortization of in-licensed rights)		13,135			8,741			6,735			5,582
Research and development		146,207			86,584			122,848			46,204
Selling, general and administrative		64,220			53,044			47,156			43,341
Amortization of in-licensed rights		216			216			217			216
Total cost and operating expenses		223,778			148,585			176,956			95,343
Operating loss		(139,363	)		(70,099	)		(103,427	)		(30,739	)
Other loss:
Interest expense and other, net		(2,311	)		(6,968	)		(5,218	)		(4,485	)
Total other loss		(2,311	)		(6,968	)		(5,218	)		(4,485	)
Loss before income (benefit) tax expense		(141,674	)		(77,067	)		(108,645	)		(35,224	)
Income tax (benefit) expense		(779	)		(674	)		622			139
Net loss	$	(140,895	)	$	(76,393	)	$	(109,267	)	$	(35,363	)

Net loss per share - basic and diluted	$	(2.05	)	$	(1.15	)	$	(1.67	)	$	(0.55	)

Weighted average number of shares of common stock used in computing basic and diluted net loss per share		68,653			66,209			65,484			64,631

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENT ACCOUNTING PRONOUNCEMENTS (Policies)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Basis of Presentation

Estimates and Uncertainties

Fair Value Measurements

•

Level 1—quoted prices for identical instruments in active markets;

•

Level 3—valuations derived from valuation techniques in which one or more significant value drivers are unobservable.

Cash and Cash Equivalents

Cash Equivalents

Only investments that are highly liquid and readily convertible to cash and have original maturities of three months or less are considered cash equivalents.

Investments

Available-For-Sale Debt Securities

Equity Investments

Accounts Receivable

Concentration of Credit Risk

Inventories

Property and Equipment

The Company generally depreciates the cost of its property and equipment using the straight-line method over the estimated useful lives of the respective assets, which are summarized as follows:

Asset Category		Useful lives
Lab equipment		5 years
Office equipment		5 years
Software and computer equipment		3 - 5 years
Furniture and fixtures		7 years
Leasehold improvements		Lesser of the useful life or the term of the respective lease
Land improvements		25 years
Land		Not depreciated
Building and improvements		30 years
Construction in Progress		Not depreciated until put into service

Intangible assets

Impairment of Long-Lived Assets

Convertible Debt

Revenue Recognition

Product revenues

Variable Consideration

•

Research and Development

Stock-Based Compensation

Income Taxes

Leases

Embedded Derivatives

Commitments and Contingencies

Recent Accounting Pronouncements

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENT ACCOUNTING PRONOUNCEMENTS (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Summary of Estimated Useful Lives of Property and Equipment

The Company generally depreciates the cost of its property and equipment using the straight-line method over the estimated useful lives of the respective assets, which are summarized as follows:

Asset Category		Useful lives
Lab equipment		5 years
Office equipment		5 years
Software and computer equipment		3 - 5 years
Furniture and fixtures		7 years
Leasehold improvements		Lesser of the useful life or the term of the respective lease
Land improvements		25 years
Land		Not depreciated
Building and improvements		30 years
Construction in Progress		Not depreciated until put into service

LICENSE AND COLLABORATION AGREEMENTS (Tables)

12 Months Ended

Dec. 31, 2019

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Total Consideration of Business Acquisition

The following table summarizes the total consideration for the asset acquisition and the value of assets acquired and liability assumed:

Consideration (in thousands)
Purchase price	$	165,000
Transactions costs and other fees		8,753
Contingent consideration		4,500
Total consideration	$	178,253

Assets Acquired (in thousands)
Cash and cash equivalents	$	1,197
Prepaids		3,816
In-process research and development		173,240
Total assets acquired	$	178,253

Liability Assumed (in thousands)
Contingent consideration		4,500
Total liability assumed	$	4,500

FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Assets and Liabilities Measured and Carried at Fair Value

	Fair Value Measurement as of December 31, 2019
	Total		Level 1		Level 2		Level 3
	(in thousands)
Assets
Money market funds	$	203,410	$	203,410	$	—	$	—
Government and government agency bonds		809,159		809,159		—		—
Strategic equity investments		31,937		1,937		—		30,000
Certificates of deposit		1,001		1,001		—		—
Total assets	$	1,045,507	$	1,015,507	$	—	$	30,000

Liabilities
Contingent consideration		5,200		—		—		5,200
Total liabilities	$	5,200	$	—	$	—	$	5,200

	Fair Value Measurement as of December 31, 2018
	Total		Level 1		Level 2		Level 3
	(in thousands)
Assets
Money market funds	$	42,920	$	42,920	$	—	$	—
Commercial paper		125,907		—		125,907		—
Government and government agency bonds		760,235		760,235		—		—
Corporate bonds		43,468		43,468		—		—
Strategic equity investments		31,739		1,739		—		30,000
Certificates of deposit		1,001		1,001		—		—
Total	$	1,005,270	$	849,363	$	125,907	$	30,000

- Definition

Tabular disclosure of financial instruments measured at fair value, including those classified in shareholders' equity measured on a recurring or nonrecurring basis. Disclosures include, but are not limited to, fair value measurements recorded and the reasons for the measurements, level within the fair value hierarchy in which the fair value measurements are categorized and transfers between levels 1 and 2. Nonrecurring fair value measurements are those that are required or permitted in the statement of financial position in particular circumstances.

+ References + Details

CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES (Tables)

12 Months Ended

Dec. 31, 2019

Cash And Cash Equivalents [Abstract]

Summary of Company Financial Assets with Maturities of Less Than 90 Days Included in Cash Equivalents

	As of December 31,
	2019		2018
	(in thousands)
Money market funds	$	203,410	$	42,920
Government and government agency bonds		519,491		111,587
Commercial paper		—		14,940
Total	$	722,901	$	169,447

Summary of Company Cash, Cash Equivalents and Investments

The following tables summarize the Company’s cash, cash equivalents and investments for each of the periods indicated:

	As of December 31, 2019
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Market Value
	(in thousands)
Cash and money market funds	$	315,589	$	—	$	—		$	315,589
Government and government agency bonds		809,090		71		(2	)		809,159
Total cash, cash equivalents and investments	$	1,124,679	$	71	$	(2	)	$	1,124,748
As reported:
Cash and cash equivalents	$	835,044	$	36	$	—		$	835,080
Short-term investments		289,635		35		(2	)		289,668
Total cash, cash equivalents and investments	$	1,124,679	$	71	$	(2	)	$	1,124,748

	As of December 31, 2018
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Market Value
	(in thousands)
Cash and money market funds	$	244,302	$	—	$	—		$	244,302
Commercial paper		125,907		—		—			125,907
Government and government agency bonds		760,258		12		(35	)		760,235
Corporate bonds		43,544		—		(76	)		43,468
Total cash, cash equivalents and investments	$	1,174,011	$	12	$	(111	)	$	1,173,912
As reported:
Cash and cash equivalents	$	370,827	$	3	$	(1	)	$	370,829
Short-term investments		803,184		9		(110	)		803,083
Total cash, cash equivalents and investments	$	1,174,011	$	12	$	(111	)	$	1,173,912

ACCOUNTS RECEIVABLE AND RESERVES FOR PRODUCT SALES (Tables)

12 Months Ended

Dec. 31, 2019

Receivables Net Current [Abstract]

Summary of Components of Accounts Receivable

The following table summarizes the components of the Company’s accounts receivable for the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Product sales, net of discounts and allowances	$	90,409	$	48,252
Government contract receivables		470		792
Total accounts receivable, net	$	90,879	$	49,044

Summary of Change in Reserves for Discounts and Allowances

The following table summarizes an analysis of the change in reserves for discounts and allowances for the periods indicated:

	Chargebacks			Rebates			Prompt Pay			Other Accruals			Total
	(in thousands)
Balance, as of December 31, 2017	$	995		$	6,959		$	169		$	464		$	8,587
Provision		12,284			28,420			2,624			5,286			48,614
Payments/credits		(11,901	)		(11,103	)		(2,255	)		(3,432	)		(28,691	)
Balance, as of December 31, 2018	$	1,378		$	24,276		$	538		$	2,318		$	28,510
Provision		9,698			44,749			4,897			9,643			68,987
Payments/credits		(10,488	)		(24,287	)		(3,929	)		(7,290	)		(45,994	)
Balance, as of December 31, 2019	$	588		$	44,738		$	1,506		$	4,671		$	51,503

Summary of Total Reserves Included in Consolidated Balance Sheets

The following table summarizes the total reserves above included in the Company’s consolidated balance sheets for the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Reduction to accounts receivable	$	6,254	$	2,364
Component of accrued expenses		45,249		26,146
Total reserves	$	51,503	$	28,510

INVENTORY (Tables)

12 Months Ended

Dec. 31, 2019

Inventory Disclosure [Abstract]

Summary of Components of Inventory

The following table summarizes the components of the Company’s inventory for each of the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Raw materials	$	82,030	$	71,313
Work in progress		88,031		47,279
Finished goods		1,318		6,853
Total inventory	$	171,379	$	125,445

OTHER ASSETS (Tables)

12 Months Ended

Dec. 31, 2019

Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]

Summary of Other Current Assets

The following table summarizes the Company’s other current assets for each of the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Manufacturing-related deposits and prepaids	$	54,276	$	39,036
Prepaid clinical and pre-clinical expenses		8,263		9,706
Prepaid maintenance services		4,366		2,994
Leasehold improvement receivable		3,059		13,474
Prepaid insurance		2,573		1,006
Prepaid income tax		2,114		2,130
Prepaid research expenses		2,007		1,932
Other		5,249		7,504
Total other current assets	$	81,907	$	77,782

Summary of Other Non-current Assets

The following table summarizes the Company’s other non-current assets for each of the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Manufacturing-related deposits and prepaids	$	122,091	$	62,821
Strategic investments		31,937		31,739
Restricted cash and investments		9,566		1,001
Prepaid clinical expenses		4,665		7,541
Alternative minimum tax credit		3,367		3,367
Other		2,233		825
Total other non-current assets	$	173,859	$	107,294

PROPERTY AND EQUIPMENT, NET (Tables)

12 Months Ended

Dec. 31, 2019

Property Plant And Equipment [Abstract]

Summarizes Components of Property and Equipment, Net

Property and equipment are recorded at historical cost, net of accumulated depreciation. The following table summarizes components of property and equipment, net for each of the periods indicated:

	As of December 31,
	2019			2018
	(in thousands)
Leasehold improvements	$	53,950		$	20,937
Software and computer equipment		30,683			15,774
Lab equipment		30,053			17,659
Building and improvements		23,108			22,972
Furniture and fixtures		7,090			3,227
Land		5,183			4,158
Land improvements		3,403			—
Office equipment		1,157			436
Construction in progress		25,988			40,010
Property and equipment, gross		180,615			125,173
Less: accumulated depreciation		(50,995	)		(28,149	)
Property and equipment, net	$	129,620		$	97,024

INTANGIBLE ASSETS (Table)

12 Months Ended

Dec. 31, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

Summary of Components of Intangible Assets

The following table summarizes the components of the Company’s intangible assets for each of the periods indicated:

	As of December 31,
	2019			2018
	(in thousands)
Patents	$	8,902		$	7,227
In-licensed rights		8,073			7,573
Software licenses		1,029			626
Intangible assets, gross		18,004			15,426
Less: accumulated amortization		(5,507	)		(3,852	)
Intangible assets, net	$	12,497		$	11,574

Summary of Estimated Future Amortization for Intangible Assets

The following table summarizes the estimated future amortization for intangible assets:

	As of December 31, 2019 (in thousands)
2020	$	1,358
2021		1,168
2022		1,156
2023		1,156
2024		1,149
Thereafter		6,510
Total	$	12,497

ACCRUED EXPENSES (Tables)

12 Months Ended

Dec. 31, 2019

Payables And Accruals [Abstract]

Summary of Accrued Expenses

The following table summarizes the Company’s accrued expenses for each of the periods indicated:

	As of December 31,
	2019		2018
	(in thousands)
Product revenue related reserves	$	45,249	$	26,146
Accrued employee compensation costs		43,240		24,692
Accrued contract manufacturing costs		27,622		15,794
Accrued milestone expense		18,390		24,020
Accrued clinical and pre-clinical costs		18,010		11,396
Accrued professional fees		10,707		11,319
Accrued collaboration cost-sharing		9,000		2,167
Accrued royalties		6,301		8,254
Other		7,008		10,307
Total accrued expenses	$	185,527	$	134,095

INDEBTEDNESS (Tables)

12 Months Ended

Dec. 31, 2019

Debt Disclosure [Abstract]

Summary of Debt Facilities

The following table summarizes the Company’s debt facilities for the periods indicated:

	As of December 31,
	2019			2018
	(in thousands)
Principal amount of the 2024 Notes	$	570,000		$	570,000
Unamortized discount - equity component		(120,182	)		(140,206	)
Unamortized discount - debt issuance costs		(7,922	)		(9,240	)
Net carrying value of 2024 Notes		441,896			420,554
Principal amount of the 2019 Term Loan		250,000			—
Unamortized discounts		(9,996	)		—
Net carrying value of 2019 Term Loan		240,004			—
Total carrying value of debt facilities		681,900			420,554
Fair value of 2024 Notes		1,141,288			952,681
Fair value of 2019 Term Loan		250,000			—
Total fair value of debt facilities	$	1,391,288		$	952,681

Summarizes Total Gross Payments Due under Company's Debt Arrangements

The following table summarizes the total gross payments due under the Company’s debt arrangements:

	As of December 31, 2019
	(in thousands)
2020	$	—
2021		—
2022		—
2023		250,000
2024		570,000
Thereafter		—
Total payments	$	820,000

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
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+ Details

STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2019

Summary of Stock Option Activity

The following tables summarize the Company’s stock option activity for each of the periods indicated:

	For the Year Ended December 31,
	2019					2018					2017
				Weighted					Weighted						Weighted
				Average					Average						Average
				Exercise					Exercise						Exercise
	Shares			Price		Shares			Price		Shares				Price
Grants outstanding at beginning of the period		8,391,171		$	46.09		8,806,204		$	29.74		5,436,951			$	22.70
Granted		1,429,652			132.97		2,152,439			90.15		4,805,722		(1)		35.09
Exercised		(1,055,715	)		30.73		(2,119,306	)		22.89		(792,845	)			17.40
Expired and forfeited		(418,760	)		84.15		(448,166	)		46.11		(643,624	)			25.44
Grants outstanding at end of the period		8,346,348		$	61.01		8,391,171		$	46.09		8,806,204			$	29.74

Grants exercisable at end of the period		2,368,621		$	45.33		2,304,791		$	27.69		3,288,712			$	24.76
Grants vested and expected to vest at end of the period		7,987,427		$	58.65		6,643,835		$	45.43		6,910,022			$	28.49

(1)	Includes 3,300,000 options with service and market conditions granted to the Company’s CEO. These options have a five-year cliff vesting schedule. The fair value of $13.48 for these options was determined by a lattice model with Monte Carlo simulations.

The weighted-average grant date fair value per share of stock options granted during the years ended December 31, 2019, 2018 and 2017 was $70.93, $44.66 and $14.78, respectively.

			Weighted
	Aggregate		Average
	Intrinsic		Remaining
	Value		Contractual
	(in thousands)		Life (Years)
Options outstanding at December 31, 2019	$	587,191	7.5
Options exercisable at December 31, 2019	$	199,438		6.0
Options vested and expected to vest at December 31, 2019	$	578,938	7.4

Summary of Company's Stock Options Vested and Exercised

The following table summarizes the Company’s stock options vested and exercised for each of the periods indicated:

	For the Year Ended December 31,
	2019		2018		2017
	(in thousands)
Aggregate grant date fair value of stock options vested	$	50,878	$	16,316	$	18,225
Aggregate intrinsic value of stock options exercised	$	109,707	$	158,936	$	20,922

Summary of Stock Appreciation Rights Activity

The following table summarizes the Company’s SAR activity for each of the periods indicated:

	For the Year Ended December 31,
	2019						2018				2017
				Weighted					Weighted				Weighted
				Average					Average				Average
				Exercise					Exercise				Exercise
	Shares			Price			Shares		Price		Shares		Price
Grants outstanding at beginning of the period		100,000		$	23.85			100,000	$	23.85		100,000	$	23.85
Exercised		(100,000	)	$	(23.85	)		—	$	—		—	$	—
Grants outstanding at end of the period		—		$	—			100,000	$	23.85		100,000	$	23.85
Grants exercisable at end of the period		—		$	—			100,000	$	23.85		100,000	$	23.85
Grants vested and expected to vest at end of the period		—		$	—			100,000	$	23.85		100,000	$	23.85

Summary of Employee Stock Purchase Plan Activity and Expense

The following table summarizes the Company’s ESPP activity for each of the periods indicated:

	For the Year Ended December 31,
	2019		2018		2017
Number of shares purchased		92,086		75,094		102,698
Proceeds received (in millions)	$	5.1	$	2.3	$	1.4

Summary of Stock-Based Compensation Expense by Function Included within Consolidated Statements of Operations and Comprehensive Loss

The following table summarizes stock-based compensation expense by function included within the consolidated statements of operations and comprehensive loss:

	For the Year Ended December 31,
	2019		2018		2017
	(in thousands)
Research and development	$	27,681	$	14,214	$	8,542
Selling, general and administrative		50,921		35,913		21,923
Total stock-based compensation	$	78,602	$	50,127	$	30,465

Summary of Stock-Based Compensation Expense by Grant Type Included within Consolidated Statements of Operations and Comprehensive Loss

The following table summarizes stock-based compensation expense by grant type included within the consolidated statements of operations and comprehensive loss:

	For the Year Ended December 31,
	2019		2018		2017
	(in thousands)
Stock options	$	53,427	$	37,671	$	23,416
Restricted stock awards/units		20,103		10,632		5,295
Employee stock purchase plan		5,072		1,824		1,754
Total stock-based compensation	$	78,602	$	50,127	$	30,465

Restricted Stock Awards (RSAs) [Member]

Summary of Restricted Stock Award and Restricted Stock Units Activity

The following table summarizes the Company’s RSA activity for each of the periods indicated:

	For the Year Ended December 31,
	2019					2018					2017
				Weighted					Weighted					Weighted
				Average					Average					Average
				Grant Date					Grant Date					Grant Date
	Shares			Fair Value		Shares			Fair Value		Shares			Fair Value
Grants outstanding at beginning of the period		252,321		$	42.37		411,781		$	37.23		153,170		$	34.53
Granted		—			—		27,590			98.57		341,500			34.58
Vested		(100,840	)		40.54		(187,050	)		39.34		(63,264	)		14.60
Cancelled		(15,356	)		48.94		—			—		(19,625	)		43.02
Grants outstanding at end of the period		136,125		$	42.98		252,321		$	42.37		411,781		$	37.23

Restricted Stock Units (RSUs) [Member]

Summary of Restricted Stock Award and Restricted Stock Units Activity

The following table summarizes the Company’s RSU activity for the periods indicated:

	For the Year Ended December 31,
	2019					2018					2017
				Weighted					Weighted					Weighted
				Average					Average					Average
				Grant Date					Grant Date					Grant Date
	Shares			Fair Value		Shares			Fair Value		Shares			Fair Value
Grants outstanding at beginning of the period		251,298		$	81.21		66,552		$	33.72		—		$	—
Granted		511,283			131.18		230,736			87.95		181,029			33.03
Vested		(84,068	)		75.12		(30,276	)		33.23		(78,017	)		32.63
Cancelled		(72,639	)		103.03		(15,714	)		71.45		(36,460	)		32.63
Grants outstanding at end of the period		605,874		$	121.61		251,298		$	81.21		66,552		$	33.72

Stock Options [Member]

Assumptions for Measuring Fair Values of Stocks

The fair values of stock options granted during the periods presented are measured on the date of grant using the Black-Scholes-Merton option-pricing model, with the following assumptions:

	For the Year Ended December 31,
	2019	2018	2017
Risk-free interest rate (1)	1.4 - 2.5%	2.5 - 3.0%	1.6 - 2.1%
Expected dividend yield (2)	—	—	—
Expected term (3)	5.04 years	5.06 years	4.2 - 4.8 years
Expected volatility (4)	52.5 - 68.9%	52.4 - 60.8%	54.0 - 63.0%

(1)	The risk-free interest rate is estimated using an average of Treasury bill interest rates over a historical period commensurate with the expected term of the option that correlates to the prevailing interest rates at the time of grant.

(2)	The expected dividend yield is zero as the Company has not paid any dividends to date and does not expect to pay dividends in the future.

(3)	The expected term is estimated using historical exercise behavior.

(4)	The expected volatility is the implied volatility in exchange-traded options of the Company’s common stock.

OTHER (LOSS) INCOME (Tables)

12 Months Ended

Dec. 31, 2019

Other Income And Expenses [Abstract]

Summary of Other Income and Loss

The following table summarizes other income and loss for the periods indicated:

	For the Year Ended December 31,
	2019			2018			2017
	(in thousands)
Interest expense	$	(30,669	)	$	(33,709	)	$	(5,801	)
Interest income		7,238			6,810			1,809
Amortization of investment discount		15,350			8,573			1,401
Other expense		(236	)		(656	)		601
Gain from sale of Priority Review Voucher		—			—			125,000
Total other (loss) income	$	(8,317	)	$	(18,982	)	$	123,010

INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2019

Income Tax Disclosure [Abstract]

Summary of Loss before Provision for Income Taxes by Jurisdiction

The following table summarizes the loss before the provision for income taxes by jurisdiction for the periods indicated:

	For the Year Ended December 31,
	2019			2018			2017
	(in thousands)
Domestic	$	(489,747	)	$	(309,294	)	$	(45,686	)
Foreign		(224,133	)		(53,316	)		(2,942	)
Total	$	(713,880	)	$	(362,610	)	$	(48,628	)

Summary of Provision for Income Taxes

The following table summarizes provision for income taxes in the accompanying consolidated financial statements for the periods indicated:

	For the Year Ended December 31,
	2019			2018			2017
	(in thousands)
Current provision:
Federal	$	—		$	(110	)	$	204
State		521			(653	)		1,856
Foreign		1,050			311			—
Total current provision		1,571			(452	)		2,060
Deferred benefit:
Federal		(15	)		—			—
State		(5	)		—			—
Foreign		(356	)		(240	)		—
Total deferred benefit		(376	)		(240	)		—
Total current provision	$	1,195		$	(692	)	$	2,060

Reconciliation Between Effective Tax Rate and Federal Income Tax Rate

The following table summarizes the reconciliation between the Company’s effective tax rate and the income tax rate for each of the periods indicated:

	For the Year Ended December 31,
	2019				2018				2017
Federal income tax rate		21.0		%		21.0		%		34.0		%
State taxes		6.3				12.3				(27.7	)
Research and development and other tax credits		3.3				3.1				8.5
Valuation allowance		(16.8	)			(45.5	)			(93.2	)
Permanent differences		1.8				6.9				6.4
Sarepta International C.V. return to provision		—				(0.1	)			62.1
Impact of tax reform, net of valuation allowance		—				—				5.9
Basis difference in subsidiary		(8.4	)			—				—
Foreign rate differential		(7.4	)			(0.9	)			(0.6	)
Other		—				3.4				0.4
Effective tax rate		(0.2	)	%		0.2		%		(4.2	)	%

Analysis of Deferred Tax Assets and Liabilities

The following table summarizes the analysis of the deferred tax assets and liabilities for each of the periods indicated:

	As of December 31,
	2019			2018
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	304,033		$	212,342
Difference in depreciation and amortization		40,095			55,162
Research and development tax credits		103,806			67,309
Stock-based compensation		24,114			15,538
Lease liabilities		15,796			4,831
Deferred revenue		939			888
Capitalized inventory		18,255			22,943
Other		16,270			15,727
Total deferred tax assets		523,308			394,740
Deferred tax liabilities:
Right of use asset		(10,782	)		—
Debt discount		(23,099	)		(25,162	)
Total deferred tax liabilities		(33,881	)		(25,162	)
Valuation allowance		(488,829	)		(369,345	)
Net deferred tax assets	$	598		$	233

Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits

The follow table summarizes the reconciliation of the beginning and ending amount of total unrecognized tax benefits for each of the periods indicated:

	For the Year Ended December 31,
	2019			2018		2017
	(in thousands)
Balance at beginning of the period	$	37,544		$	5,134	$	4,644
Increase related to current year tax positions		4,275			2,164		735
Increase related to prior year tax positions		109			30,246		—
Decrease related to prior year tax positions		(175	)		—		(245	)
Balance at end of the period	$	41,753		$	37,544	$	5,134

LEASES (Tables)

12 Months Ended

Dec. 31, 2019

Leases [Abstract]

Summary of Lease Costs Recognized Under Topic 842 and Other Information Pertaining to Operating Leases

The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the year ended December 31, 2019:

	For the Year Ended December 31, 2019
	(in thousands)
Lease cost
Operating lease cost	$	10,335
Variable lease cost		3,967
Total lease cost	$	14,302

Other information
Operating lease payments		10,416
Operating lease liabilities arising from obtaining ROU assets		—
Weighted average remaining lease term	5.5
Weighted average discount rate		7.50	%

Summary of Maturities of Lease Liabilities and Reconciliation of Lease Liabilities Recognized Under Topic 842

The following table summarizes maturities of lease liabilities and the reconciliation of lease liabilities as of December 31, 2019:

	As of December 31, 2019
	(in thousands)
2020	$	11,718
2021		12,891
2022		11,080
2023		11,230
2024		11,471
Thereafter		9,654
Total minimum lease payments		68,044
Less: imputed interest		(12,478	)
Total operating lease liabilities	$	55,566
Included in the condensed consolidated balance sheet:
Current portion of lease liabilities within other current liabilities	$	7,846
Lease liabilities		47,720
Total operating lease liabilities	$	55,566

Summary of Aggregate Future Minimum Non-Cancellable Commitments Under Leases

For comparable purposes, aggregate future minimum non-cancellable commitments under leases as of December 31, 2018, are as follows:

	As of December 31, 2018
	(in thousands)
2020	$	11,395
2021		12,558
2022		10,757
2023		10,898
2024		11,128
Thereafter		9,396
Total minimum lease payments	$	66,132

NET LOSS PER SHARE (Tables)

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Basic and Diluted Net Loss Per Share

Given that the Company recorded a net loss for each of the periods presented, there is no difference between basic and diluted net loss per share since the effect of common stock equivalents would be anti-dilutive and are, therefore, excluded from the diluted net loss per share calculation.

	For the Year Ended December 31,
	2019			2018			2017
	(in thousands, except per share amounts)
Net loss	$	(715,075	)	$	(361,918	)	$	(50,688	)
Weighted-average common shares outstanding - basic		73,615			66,250			58,818
Effect of dilutive securities*		—			—			—
Weighted-average common shares outstanding - diluted		73,615			66,250			58,818
Net loss per share — basic and diluted	$	(9.71	)	$	(5.46	)	$	(0.86	)

COMMITMENTS AND CONTINGENCIES (Tables)

12 Months Ended

Dec. 31, 2019

Commitments And Contingencies Disclosure [Abstract]

Summary of Aggregate Non-Cancelable Contractual Obligations Arising from Manufacturing Obligations

The following table presents non-cancelable contractual obligations arising from long-term contractual arrangements:

	As of December 31, 2019 (in thousands)
2020	$	378,744
2021		183,661
2022		64,653
2023		58,319
2024		58,309
Thereafter		149,350
Total manufacturing commitments	$	893,036

FINANCIAL INFORMATION BY QUARTER (UNAUDITED) (Tables)

12 Months Ended

Dec. 31, 2019

Quarterly Financial Information Disclosure [Abstract]

Financial Information by Quarter

	2019 for Quarter Ended
	December 31			September 30			June 30			March 31
	(in thousands)
Revenues:
Product, net	$	100,113		$	99,041		$	94,668		$	87,011
Total revenues		100,113			99,041			94,668			87,011

Cost and expenses:
Cost of sales (excluding amortization of in-licensed rights)		15,567			13,037			15,919			12,063
Research and development		223,141			133,949			113,266			90,553
Selling, general and administrative		81,424			75,429			67,393			60,566
Acquired in-process research and development		—			—			173,240			—
Settlement and license charges		10,000			—			—			—
Amortization of in-licensed rights		200			216			217			216
Total cost and operating expenses		330,332			222,631			370,035			163,398
Operating loss		(230,219	)		(123,590	)		(275,367	)		(76,387	)
Other loss:
Other expense, net		(4,773	)		(2,510	)		(862	)		(172	)
Other loss		(4,773	)		(2,510	)		(862	)		(172	)
Loss before income tax expense		(234,992	)		(126,100	)		(276,229	)		(76,559	)
Income tax expense		711			226			174			84
Net loss	$	(235,703	)	$	(126,326	)	$	(276,403	)	$	(76,643	)

Net loss per share - basic and diluted	$	(3.16	)	$	(1.70	)	$	(3.74	)	$	(1.07	)

Weighted average number of shares of common stock used in computing basic and diluted net loss per share		74,557			74,177			73,958			71,731

	2018 for Quarter Ended
	December 31			September 30			June 30			March 31
	(in thousands)
Revenues:
Product, net	$	84,415		$	78,486		$	73,529		$	64,604
Total revenues		84,415			78,486			73,529			64,604

Cost and expenses:
Cost of sales (excluding amortization of in-licensed rights)		13,135			8,741			6,735			5,582
Research and development		146,207			86,584			122,848			46,204
Selling, general and administrative		64,220			53,044			47,156			43,341
Amortization of in-licensed rights		216			216			217			216
Total cost and operating expenses		223,778			148,585			176,956			95,343
Operating loss		(139,363	)		(70,099	)		(103,427	)		(30,739	)
Other loss:
Interest expense and other, net		(2,311	)		(6,968	)		(5,218	)		(4,485	)
Total other loss		(2,311	)		(6,968	)		(5,218	)		(4,485	)
Loss before income (benefit) tax expense		(141,674	)		(77,067	)		(108,645	)		(35,224	)
Income tax (benefit) expense		(779	)		(674	)		622			139
Net loss	$	(140,895	)	$	(76,393	)	$	(109,267	)	$	(35,363	)

Net loss per share - basic and diluted	$	(2.05	)	$	(1.15	)	$	(1.67	)	$	(0.55	)

Weighted average number of shares of common stock used in computing basic and diluted net loss per share		68,653			66,209			65,484			64,631

Organization and Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Cash, cash equivalents and investments	$ 1,134,400
Cash and cash equivalents	835,080	$ 370,829	$ 599,691
Short-term investments	289,668	803,083
Restricted cash and investments	$ 9,566	$ 1,001

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) Segment	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments \| Segment	1
Right-of-use assets	$ 37,933			$ 42,500
Operating lease liabilities	$ 55,566			$ 60,100
Employee Stock Purchase Plan [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of closing price of common stock	85.00%
Percentage of discount recognized on graded-vesting based on stock-based compensation expense over the purchase period	15.00%
Patents [Member]
Summary Of Significant Accounting Policies [Line Items]
Initial term of patents	20 years
Product Revenues [Member] \| Customer One [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	43.00%	42.00%	47.00%
Product Revenues [Member] \| Customer Two [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	41.00%	38.00%	34.00%
Product Revenues [Member] \| Customer Three [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	13.00%	18.00%	19.00%
Accounts Receivable [Member] \| Customer One [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	45.00%	51.00%
Accounts Receivable [Member] \| Customer Two [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	37.00%	28.00%
Accounts Receivable [Member] \| Customer Three [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	11.00%	10.00%
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable payment term	60 days
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable payment term	91 days
Outside of U.S. [Member] \| Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable payment term	45 days
Outside of U.S. [Member] \| Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable payment term	150 days

Summary of Estimated Useful Lives of Plant and Equipment (Detail)	12 Months Ended
	Dec. 31, 2018
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life	5 years
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life	5 years
Software and Computer Equipment [Member] \| Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life	3 years
Software and Computer Equipment [Member] \| Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life	Lesser of the useful life or the term of the respective lease
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life	7 years
Land [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life	Not depreciated
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life	25 years
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life	Not depreciated until put into service
Building and Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, Estimated useful life	30 years

License and Collaboration Agreements - Additional Information (Detail)					1 Months Ended					3 Months Ended								12 Months Ended
	Dec. 21, 2019 USD ($)	Nov. 14, 2019 USD ($) shares	Apr. 04, 2019	Feb. 27, 2019 USD ($)	Oct. 31, 2018 USD ($) shares	May 31, 2018 USD ($)	Jul. 31, 2017 USD ($)	May 31, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2019 USD ($) shares	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) shares	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) Milestone shares	Dec. 31, 2018 USD ($) Milestone shares	Dec. 31, 2017 USD ($)	Nov. 22, 2019	Aug. 08, 2018 USD ($) shares
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense										$ 223,141,000	$ 133,949,000	$ 113,266,000	$ 90,553,000	$ 146,207,000	$ 86,584,000	$ 122,848,000	$ 46,204,000
Common stock, issued \| shares										75,184,863				71,071,887				75,184,863	71,071,887
Common stock, $.0001 par value, 99,000,000 shares authorized; 75,184,863 and 71,071,887 issued and outstanding at December 31, 2019 and 2018, respectively										$ 8,000				$ 7,000				$ 8,000	$ 7,000
Contingent consideration liability of acquisition										5,200,000								5,200,000
Intangible asset, net										12,497,000				11,574,000				12,497,000	11,574,000
Settlement and license charges										10,000,000								10,000,000		$ 28,427,000
Amortization of in-licensed rights										200,000	$ 216,000	217,000	$ 216,000	216,000	$ 216,000	$ 217,000	$ 216,000	849,000	865,000	1,053,000
Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalty payments							8.00%
Amortization of in-licensed rights																				1,100,000
Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalty payments							4.00%
StrideBio, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front cash payment under agreements		$ 17,500,000
Up-front cash expense		$ 46,900,000
Common stock, issued \| shares		301,980
Common stock, $.0001 par value, 99,000,000 shares authorized; 75,184,863 and 71,071,887 issued and outstanding at December 31, 2019 and 2018, respectively		$ 29,400,000
Up-front cash payment under development		450,000,000.0
Up-front cash payment under sales milestone		835,000,000.0
Up-front cash payment under agreements		46,900,000
StrideBio, Inc. [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front cash payment under agreements		$ 42,500,000
Myonexus Therapeutics, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Final exercise price				$ 165,000,000.0
Additional transaction fees				8,800,000						165,000,000								165,000,000
Additional development milestone payments to be paid				200,000,000.0
Date of acquisition			Apr. 04, 2019
Contingent consideration liability of acquisition				$ 4,500,000						4,500,000								4,500,000
Lacerta Therapeutics [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense																		$ 0
Number of development milestone \| Milestone																		0
BioMarin Pharmaceutical, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front cash payment under agreements							$ 35,000,000.0
Regulatory and sales milestone payments																		$ 0	0	0
Intangible asset, net																				6,600,000
Settlement and license charges																				28,400,000
Regulatory milestone payable										10,000,000.0								10,000,000.0
Sales milestone payment recorded as an in-license right										0								0
Royalty expense																		19,400,000	15,100,000	4,700,000
BioMarin Pharmaceutical, Inc. [Member] \| Intellectual Property
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amortization of in-licensed rights																		4,200,000
BioMarin Pharmaceutical, Inc. [Member] \| US [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty payment expiry period							2024-03
BioMarin Pharmaceutical, Inc. [Member] \| EU [member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty payment expiry period							2024-12
BioMarin Pharmaceutical, Inc. [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and sales milestone payments							$ 65,000,000.0
BioMarin Pharmaceutical, Inc. [Member] \| Maximum [Member] \| Other Countries [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty payment expiry period							2024-12
University of Western Australia [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and sales milestone payments																		0
Sales milestone payment recorded as an in-license right										0								0
Royalty expense																		3,500,000	0	0
Carrying value of intangible assets										1,100,000								1,100,000
University of Western Australia [Member] \| EXONDYS 51
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sales milestone payment recorded as an in-license right										1,000,000.0								1,000,000.0
University of Western Australia [Member] \| VYONDYS 53 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sales milestone payment recorded as an in-license right										500,000								500,000
University of Western Australia [Member] \| Maximum [Member] \| EXONDYS 51
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payments to UWA on successful achievement of certain development and regulatory milestones									$ 26,000,000.0
Collaborative Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage in development costs																					0.75
Collaborative Arrangement \| Roche Holding A.G. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds From License And Collaborative Agreement	$ 1,200,000,000
Upfront Cash Payment Received	750,000,000.0
Stock Issued During Period Value Collaboration and License Agreement	400,000,000.0
Collaborative Arrangement \| Roche Holding A.G. [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Regulatory and Sales Milestones Payment Received	1,700,000,000
Option exercise payment	125,000,000.0
Collaborative Arrangement \| Roche Holding A.G. [Member] \| Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Option exercise payment	$ 20,000,000.0
Collaborative Arrangement \| Genethon [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage in development costs																					0.25
Research and development expense																		9,000,000.0
Up-front cash payment under agreements								$ 28,000,000.0
Collaborative Arrangement \| Genethon [Member] \| Genethon Products [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payment								157,500,000
Collaborative Arrangement \| Genethon [Member] \| Other Licensed Products [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payment								$ 78,800,000
Collaborative Arrangement \| Lysogene S.A. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense																			44,800,000
Upfront License Fee														26,100,000					26,100,000
Development milestone payment																			18,700,000
Collaborative Arrangement \| University of Western Australia [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development Milestone and Settlement Upfront Fee Recognized as Research and Development Expense																		113,200,000	142,400,000	$ 22,000,000.0
Collaborative Arrangement \| University of Western Australia [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory, commercial milestone and up-front royalty payments										3,000,000,000.0								3,000,000,000.0
Warrant Agreement \| Myonexus Therapeutics, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense																			85,000,000.0
Up-front cash payment under agreements						$ 60,000,000.0													60,000,000.0
Cash consideration under agreement excluding contingent payments						$ 200,000,000.0
Up-front cash payment under sales milestone																			20,000,000.0
Milestone accrued payment														5,000,000.0					$ 5,000,000.0
Number of development milestone \| Milestone																			2
Additional development milestone payments to be paid										200,000,000.0								200,000,000.0
Cost of asset												$ 173,200,000
Equity Investment Agreement [Member] \| Lysogene S.A. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments to be paid					$ 102,800,000
Common stock purchased,shares \| shares					950,606
Percentage of common stock outstanding					8.00%
Equity Investment Agreement [Member] \| Lysogene S.A. [Member] \| Other Noncurrent Assets [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront License Fee														$ 1,900,000					$ 1,900,000
Equity Investment Agreement [Member] \| Lacerta Therapeutics [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Investment change in carrying value																		0	$ 0
License Development And Option Agreement \| Lacerta Therapeutics [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front payment																						$ 42,000,000.0
Pompe License Agreement \| Lacerta Therapeutics [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front payment																						8,000,000.0
Pompe License Agreement \| Lacerta Therapeutics [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front payment																						$ 44,000,000.0
Series A Preferred Stock Purchase Agreement \| Lacerta Therapeutics [Member] \| Series A Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front payment \| shares																						4,500,000
Series A Preferred Stock Purchase Agreement \| Lacerta Therapeutics [Member] \| Other Noncurrent Assets [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front payment																						$ 30,000,000.0
License And Purchase Agreement \| Lacerta Therapeutics [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front payment																						$ 38,000,000.0
Nationwide License Agreement [Member] \| Nationwide Children’s Hospital [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development expense																		0
Up-front cash payment under agreements					$ 1,000,000.0
Development, regulatory and sales milestones payments to be paid										$ 0								$ 0
Nationwide License Agreement [Member] \| Nationwide Children’s Hospital [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments to be paid					$ 29,000,000.0

Schedule of Total Consideration of Business Acquisition (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019	Feb. 27, 2019
Consideration
Contingent consideration liability of acquisition		$ 5,200
Assets Acquired (in thousands)
In-process research and development	$ 173,240	173,240
Myonexus Therapeutics, Inc. [Member]
Consideration
Additional transaction fees		165,000	$ 8,800
Transactions costs and other fees		8,753
Contingent consideration liability of acquisition		4,500	$ 4,500
Total consideration		178,253
Assets Acquired (in thousands)
Cash and cash equivalents		1,197
Prepaids		3,816
In-process research and development		173,240
Total assets acquired		178,253
Liability Assumed
Contingent consideration		4,500
Total liability assumed		$ 4,500

Gain From Sale of Priority Review Voucher - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017
Gain From Sale Of Intangible Asset [Line Items]
Gain from sale of PRV asset		$ 125,000
Gilead [Member]
Gain From Sale Of Intangible Asset [Line Items]
Gain from sale of PRV asset	$ 125,000

Assets and Liabilities Measured and Carried at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 1,045,507	$ 1,005,270
Contingent consideration	5,200
Total liabilities	5,200
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	203,410	42,920
Government and Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	809,159	760,235
Strategic Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	31,937	31,739
Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	1,001	1,001
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		125,907
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		43,468
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	1,015,507	849,363
Level 1 [Member] \| Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	203,410	42,920
Level 1 [Member] \| Government and Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	809,159	760,235
Level 1 [Member] \| Strategic Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	1,937	1,739
Level 1 [Member] \| Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	1,001	1,001
Level 1 [Member] \| Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		43,468
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		125,907
Level 2 [Member] \| Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		125,907
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	30,000	30,000
Contingent consideration	5,200
Total liabilities	5,200
Level 3 [Member] \| Strategic Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 30,000	$ 30,000

Summary of Company Financial Assets with Maturities of Less Than 90 Days Included in Cash Equivalents (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash equivalents	$ 722,901	$ 169,447
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash equivalents	203,410	42,920
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash equivalents	$ 519,491	111,587
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Cash equivalents		$ 14,940

Cash, Cash Equivalents and Marketable Securities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash And Cash Equivalents [Abstract]
Weighted average maturity period of available-for-sale securities	2 months	2 months

Summary of Company Cash, Cash Equivalents and Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	$ 835,044	$ 370,827
Cash and cash equivalents, Gross unrealized gains	36	3
Cash and cash equivalents, Gross unrealized losses		(1)
Cash and cash equivalents	835,080	370,829	$ 599,691
Cash, cash equivalents and investments, Amortized cost	1,124,679	1,174,011
Cash, cash equivalents and investments, Gross unrealized gains	71	12
Cash, cash equivalents and investments, Gross unrealized losses	(2)	(111)
Cash, cash equivalents and investments, Fair market value	1,124,748	1,173,912
Available for sale debt securities current, Amortized cost	289,635	803,184
Available for sale debt securities current, Gross unrealized gains	35	9
Available for sale debt securities current, Gross unrealized losses	(2)	(110)
Available for sale debt securities current, Fair market value	289,668	803,083
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	315,589	244,302
Cash and cash equivalents	315,589	244,302
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost		125,907
Available for sale debt securities, Fair market value		125,907
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost	809,090	760,258
Available for sale debt securities, Gross unrealized gains	71	12
Available for sale debt securities, Gross unrealized losses	(2)	(35)
Available for sale debt securities, Fair market value	$ 809,159	760,235
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost		43,544
Available for sale debt securities, Gross unrealized losses		(76)
Available for sale debt securities, Fair market value		$ 43,468

Summary of Components of Accounts Receivable (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Receivables Net Current [Abstract]
Product sales, net of discounts and allowances	$ 90,409	$ 48,252
Government contract receivables	470	792
Total accounts receivable, net	$ 90,879	$ 49,044

Summary of Change in Reserves for Discounts and Allowances (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	$ 28,510	$ 8,587
Provision	68,987	48,614
Payments/credits	(45,994)	(28,691)
Ending balance	51,503	28,510
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	1,378	995
Provision	9,698	12,284
Payments/credits	(10,488)	(11,901)
Ending balance	588	1,378
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	24,276	6,959
Provision	44,749	28,420
Payments/credits	(24,287)	(11,103)
Ending balance	44,738	24,276
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	538	169
Provision	4,897	2,624
Payments/credits	(3,929)	(2,255)
Ending balance	1,506	538
Other Accruals [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance	2,318	464
Provision	9,643	5,286
Payments/credits	(7,290)	(3,432)
Ending balance	$ 4,671	$ 2,318

Summary of Total Reserves Included in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Receivables Net Current [Abstract]
Reduction to accounts receivable	$ 6,254	$ 2,364
Component of accrued expenses	45,249	26,146
Total reserves	$ 51,503	$ 28,510	$ 8,587

Inventory - Summary of Components of Inventory (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 82,030	$ 71,313
Work in progress	88,031	47,279
Finished goods	1,318	6,853
Total inventory	$ 171,379	$ 125,445

Summary of Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Prepaid Expense And Other Assets Current [Abstract]
Manufacturing-related deposits and prepaids	$ 54,276	$ 39,036
Prepaid clinical and pre-clinical expenses	8,263	9,706
Prepaid maintenance services	4,366	2,994
Leasehold improvement receivable	3,059	13,474
Prepaid insurance	2,573	1,006
Prepaid income tax	2,114	2,130
Prepaid research expenses	2,007	1,932
Other	5,249	7,504
Total other current assets	$ 81,907	$ 77,782

Summary of Other Non-current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Prepaid Expense And Other Assets Noncurrent [Abstract]
Manufacturing-related deposits and prepaids	$ 122,091	$ 62,821
Strategic investments	31,937	31,739
Restricted cash and investments	9,566	1,001
Prepaid clinical expenses	4,665	7,541
Alternative minimum tax credit	3,367	3,367
Other	2,233	825
Total other non-current assets	$ 173,859	$ 107,294

Summarizes Components of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 180,615	$ 125,173
Less: accumulated depreciation	(50,995)	(28,149)
Property and equipment, net	129,620	97,024
Land [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,183	4,158
Building and Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	23,108	22,972
Software and Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	30,683	15,774
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	30,053	17,659
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,090	3,227
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,157	436
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	53,950	20,937
Land Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,403
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 25,988	$ 40,010

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Depreciation expense	$ 22.8	$ 10.2	$ 6.4

Intangible Assets - Summary of Components of Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 18,004	$ 15,426
Less: accumulated amortization	5,507	3,852
Intangible assets, net	12,497	11,574
Patents [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	8,902	7,227
In-Licensed Rights [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	8,073	7,573
Software Licenses [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 1,029	$ 626

Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jul. 31, 2017
Finite Lived Intangible Assets [Line Items]
Amortization of in-licensed rights	$ 200,000	$ 216,000	$ 217,000	$ 216,000	$ 216,000	$ 216,000	$ 217,000	$ 216,000	$ 849,000	$ 865,000	$ 1,053,000
Patents [Member]
Finite Lived Intangible Assets [Line Items]
Amortization of in-licensed rights									400,000	700,000	600,000
Patents [Member] \| Research and Development [Member]
Finite Lived Intangible Assets [Line Items]
Book value of patent abandoned									200,000	100,000	600,000
Impairment loss on patent assets									0	3,800,000	0
Bio Marin [Member]
Finite Lived Intangible Assets [Line Items]
Amortization of in-licensed rights									1,700,000	$ 2,100,000	1,700,000
Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Amortization of in-licensed rights											$ 1,100,000
EXONDYS 51 [Member]
Finite Lived Intangible Assets [Line Items]
In-lincensed Rights									1,000,000.0
EXONDYS 51 [Member] \| Maximum [Member] \| Bio Marin [Member]
Finite Lived Intangible Assets [Line Items]
Sales milestone payment recorded as an in-license right												$ 6,600,000
VYONDYS 53 [Member]
Finite Lived Intangible Assets [Line Items]
In-lincensed Rights									$ 500,000

Intangible Assets - Summary of Estimated Future Amortization for Intangible Assets (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Goodwill And Intangible Assets Disclosure [Abstract]
2020	$ 1,358
2021	1,168
2022	1,156
2023	1,156
2024	1,149
Thereafter	6,510
Total	$ 12,497

Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Product revenue related reserves	$ 45,249	$ 26,146
Accrued employee compensation costs	43,240	24,692
Accrued contract manufacturing costs	27,622	15,794
Accrued milestone expense	18,390	24,020
Accrued clinical and pre-clinical costs	18,010	11,396
Accrued professional fees	10,707	11,319
Accrued collaboration cost-sharing	9,000	2,167
Accrued royalties	6,301	8,254
Other	7,008	10,307
Total accrued expenses	$ 185,527	$ 134,095

Indebtedness - Additional Information (Detail)			1 Months Ended	12 Months Ended
Indebtedness - Additional Information (Detail)	Dec. 13, 2019 USD ($) Tranch	Nov. 14, 2017 USD ($) shares $ / shares	Sep. 30, 2018 USD ($)	Dec. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jul. 31, 2017 USD ($)
Debt Instrument [Line Items]
Debt instrument, face amount				$ 820,000,000
Proceeds for issuance of notes allocated to equity						$ 570,000,000
Amount paid for capped calls transactions						50,901,000
Prepayment fee percentage				2.00%
Line of credit facility, lenders fee				1.75%
Debt extinguishment loss			$ (2,300,000)		$ (2,322,000)
Long-term debt				$ 681,900,000	420,554,000
Convertible Debt, The Term Loan, The Revolver and The Mortgage Loans [Member]
Debt Instrument [Line Items]
Long-term debt				681,900,000
Interest expense related to debt facilities				30,700,000	33,700,000	$ 5,800,000
2024 Convertible Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		$ 570,000,000.0		$ 570,000,000	$ 570,000,000
Debt instrument, maturity date		Nov. 15, 2024
Debt instrument, interest rate per annum		1.50%
Debt instrument, payment frequency				The 2024 Notes were issued at face value and bear interest at the rate of 1.50% per annum, payable semi-annually in cash on each May 15 and November 15, commencing on May 15, 2018.
Debt instrument, conversion rate		0.013621
Debt instrument, conversion price \| $ / shares		$ 73.42		$ 73.42
Proceeds for issuance of notes allocated to equity		$ 161,100,000
Offering costs		4,200,000
Debt issuance costs		$ 10,600,000
Effective interest rate percentage				6.90%	6.90%	6.90%
Capped calls strike price \| $ / shares		73.42
Capped calls cap price \| $ / shares		104.88
Amount paid for capped calls transactions		$ 50,900,000
Debt discount				$ 120,182,000	$ 140,206,000
Debt issuance costs				7,922,000	$ 9,240,000
Credit agreement interest rate per annum		1.50%
2024 Convertible Notes [Member] \| Fundamental Change [Member]
Debt Instrument [Line Items]
Debt instrument, repurchase price percentage		100.00%
2024 Convertible Notes [Member] \| Minimum [Member] \| Beneficial Owner [Member] \| Fundamental Change [Member]
Debt Instrument [Line Items]
Voting percentage		50.00%
2024 Convertible Notes [Member] \| Common Stock [Member]
Debt Instrument [Line Items]
Debt instrument, convertible into shares \| shares		7,763,552
Biopharma Credit PLC and Biopharma Credit Investments V (Master) LP [Member] \| December 2019 Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Dec. 20, 2023
Debt instrument, interest rate per annum	8.50%
Current borrowing capacity	$ 500,000,000.0
Number of tranches \| Tranch	2
Prepayment fee percentage	2.00%
Debt discount				9,400,000
Debt issuance costs				700,000
Proceeds after debt discount and issuance cost				$ 244,900,000
Credit agreement interest rate per annum	8.50%
Biopharma Credit PLC and Biopharma Credit Investments V (Master) LP [Member] \| December 2019 Term Loan [Member] \| Tranch A [Member]
Debt Instrument [Line Items]
Current borrowing capacity	$ 250,000,000.0
Line of credit facility, lenders fee	1.75%
Biopharma Credit PLC and Biopharma Credit Investments V (Master) LP [Member] \| December 2019 Term Loan [Member] \| Tranch B [Member]
Debt Instrument [Line Items]
Current borrowing capacity	$ 250,000,000.0
Line of credit facility, lenders fee	1.75%
Biopharma Credit PLC and Biopharma Credit Investments V (Master) LP [Member] \| Minimum [Member] \| December 2019 Term Loan [Member]
Debt Instrument [Line Items]
Prepayment fee percentage	1.00%
Biopharma Credit PLC and Biopharma Credit Investments V (Master) LP [Member] \| Maximum [Member] \| December 2019 Term Loan [Member]
Debt Instrument [Line Items]
Prepayment fee percentage	2.00%
MidCap Financial Amended and Restated Credit and Security Agreement [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate per annum							6.25%
Current borrowing capacity							$ 60,000,000.0
Credit agreement interest rate per annum							6.25%
MidCap Financial Amended and Restated Credit and Security Agreement [Member] \| Revolving Loan [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate per annum							3.95%
Current borrowing capacity							$ 40,000,000.0
Credit agreement interest rate per annum							3.95%

Indebtedness - Summary of Debt Facilities (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Nov. 14, 2017
Debt Instrument [Line Items]
Principal amount	$ 820,000,000
Total carrying value of debt facilities	681,900,000	$ 420,554,000
Total fair value of debt facilities	1,391,288,000	952,681,000
2024 Convertible Notes [Member]
Debt Instrument [Line Items]
Principal amount	570,000,000	570,000,000	$ 570,000,000.0
Unamortized discount	(120,182,000)	(140,206,000)
Unamortized discount - debt issuance costs	(7,922,000)	(9,240,000)
Net carrying value	441,896,000	420,554,000
Total fair value of debt facilities	1,141,288,000	$ 952,681,000
2019 Term Loan [Member]
Debt Instrument [Line Items]
Principal amount	250,000,000
Unamortized discount	(9,996,000)
Net carrying value	240,004,000
Total fair value of debt facilities	$ 250,000,000

Indebtedness - Summarizes Total Gross Payments Due under Company's Debt Arrangements (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Debt Disclosure [Abstract]
2023	$ 250,000
2024	570,000
Total payments	$ 820,000

Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	1 Months Ended
	Nov. 30, 2019	Mar. 31, 2019	Nov. 30, 2018	Jul. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Common stock issued	0.3
Common stock fair value					$ 8	$ 7
Common stock average price per share		$ 140.41	$ 131.00	$ 42.50
Net proceeds from issue of common stock		$ 365,400	$ 513,400	$ 354,000
Underwriting discounts, commission and offering expenses		$ 300	$ 24,600	$ 20,000
StrideBio, Inc. [Member]
Class Of Stock [Line Items]
Common stock fair value	$ 29,400
Underwritten Public Offering [Member]
Class Of Stock [Line Items]
Common stock issued		2.6	4.1	8.8
Underwritten Offering [Member]
Class Of Stock [Line Items]
Common stock issued			0.3	1.2

Stock Based Compensation - Additional Information (Detail) - USD ($)	1 Months Ended						12 Months Ended
	Jul. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Oct. 31, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2016	Jun. 30, 2016	Sep. 30, 2014	Jun. 30, 2013	Jun. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of award							10 years
Share based compensation granted under plan vest period							4 years
Weighted-average grant date fair value per share of stock-based awards, granted to employees							$ 70.93	$ 44.66	$ 14.78
Stock-based compensation expense							$ 78,602,000	$ 50,127,000	$ 30,465,000
Unrecognized stock based compensation expense							$ 181,100,000
Weighted average period expected to recognize unrecognized stock base compensation expense							3 years
Options with Service conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock based compensation expense							$ 109,500,000
Awards with Service and Market Conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock based compensation expense							22,100,000
Stock Awards or Stock Units with Service Conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock based compensation expense							49,500,000
Former Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense									2,100,000
Maximum [Member] \| Awards with Performance Conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock based compensation expense							100,000
Stock Options with Performance-based Conditions [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense							$ 100,000	$ 200,000	$ 900,000
Restricted Stock Awards (RSAs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants, Restricted stock units and awards								27,590	341,500
Grant date fair value, restricted stock units and awards								$ 98.57	$ 34.58
Restricted stock units and awards with performance conditions remaining to be vested		411,781					136,125	252,321	411,781			153,170
Restricted Stock Awards (RSAs) [Member] \| Minimum [Member] \| Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense									$ 0
Grants, Restricted stock units and awards					71,925
Share-based compensation award, expiration date		Jun. 30, 2018
Grant date fair value, restricted stock units and awards					$ 48.94
Restricted Stock Awards (RSAs) [Member] \| Maximum [Member] \| Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense								$ 3,300,000
Grants, Restricted stock units and awards					89,906
Share-based compensation award, expiration date		Jan. 01, 2019
Grant date fair value, restricted stock units and awards					$ 54.29
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants, Restricted stock units and awards							511,283	230,736	181,029
Grant date fair value, restricted stock units and awards							$ 131.18	$ 87.95	$ 33.03
Restricted stock units and awards with performance conditions remaining to be vested		66,552					605,874	251,298	66,552
Restricted Stock Units (RSUs) [Member] \| Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense							$ 500,000	$ 200,000	$ 2,900,000
Grants, Restricted stock units and awards				156,029
Restricted stock units and awards with performance conditions remaining to be vested							0
2011 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock remain available for future grant							0
Number of shares approved under the plan																16,000,000.0
2013 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock remain available for future grant							600,000
Number of shares approved under the plan										500,000			300,000		300,000
Term of award							24 months
Percentage of closing price of common stock							85.00%
2013 Employee Stock Purchase Plan [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation award, expiration date							Feb. 29, 2020
2013 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation award, expiration date							Aug. 31, 2021
2014 Employment Commencement Incentive Plan (2014 Plan) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock remain available for future grant							600,000
Number of shares approved under the plan														600,000
Number of additional shares approved under the plan	1,200,000		3,800,000			1,000,000.0
2018 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock remain available for future grant							3,400,000
Number of shares approved under the plan											2,900,000

Assumptions for Measuring Fair Values of Stocks (Detail)

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Expected dividend yield

0.00%

Stock Options [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Risk-free interest rate, minimum

^[1]

1.40%

2.50%

1.60%

Risk-free interest rate, maximum

^[1]

2.50%

3.00%

2.10%

Expected term

^[2]

5 years 14 days

5 years 21 days

Expected volatility, minimum

^[3]

52.50%

52.40%

54.00%

Expected volatility, maximum

^[3]

68.90%

60.80%

63.00%

Stock Options [Member] | Maximum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Expected term

^[2]

4 years 9 months 18 days

Stock Options [Member] | Minimum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Expected term

^[2]

4 years 2 months 12 days

[1]	The risk-free interest rate is estimated using an average of Treasury bill interest rates over a historical period commensurate with the expected term of the option that correlates to the prevailing interest rates at the time of grant.
[2]	The expected term is estimated using historical exercise behavior.
[3]	The expected volatility is the implied volatility in exchange-traded options of the Company’s common stock.

Assumptions for Measuring Fair Values of Stocks (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected dividend yield	0.00%

Summary of Stock Option Activity (Detail) - USD ($)
$ / shares in Units, $ in Thousands

12 Months Ended

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Stock Option Shares

Grants outstanding at beginning of the period

8,391,171

8,806,204

5,436,951

Granted

1,429,652

2,152,439

4,805,722

^[1]

Exercised

(1,055,715)

(2,119,306)

(792,845)

Expired and forfeited

(418,760)

(448,166)

(643,624)

Grants outstanding at end of the period

8,346,348

8,391,171

8,806,204

Grants exercisable at end of the period

2,368,621

2,304,791

3,288,712

Grants vested and expected to vest at end of the period

7,987,427

6,643,835

6,910,022

Weighted Average Exercise Price

Grants outstanding at beginning of the period

$ 46.09

$ 29.74

$ 22.70

Granted

132.97

90.15

35.09

Exercised

30.73

22.89

17.40

Expired and forfeited

84.15

46.11

25.44

Grants outstanding at end of the period

61.01

46.09

29.74

Grants exercisable at end of the period

45.33

27.69

24.76

Grants vested and expected to vest at end of the period

$ 58.65

$ 45.43

$ 28.49

Aggregate Intrinsic Value

Outstanding at end of year

$ 587,191

Exercisable at end of year

199,438

Vested and expected to vest

$ 578,938

Weighted Average Remaining Contractual Life (Years)

Outstanding at end of year

7 years 6 months

Exercisable at end of year

6 years

Vested and expected to vest

7 years 4 months 24 days

[1]	Includes 3,300,000 options with service and market conditions granted to the Company’s CEO. These options have a five-year cliff vesting schedule. The fair value of $13.48 for these options was determined by a lattice model with Monte Carlo simulations.

Summary of Stock Option Activity (Parenthetical) (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of options granted	$ 70.93	$ 44.66	$ 14.78
CEO [Member] \| Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted			3,300,000
Cliff vesting schedule			5 years
Fair value of options granted			$ 13.48

Summary of Company's Stock Options Vested and Exercised (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Aggregate grant date fair value of stock options vested	$ 50,878	$ 16,316	$ 18,225
Aggregate intrinsic value of stock options exercised	$ 109,707	$ 158,936	$ 20,922

Summary of Restricted Stock Award Activity (Detail) - Restricted Stock Awards (RSAs) [Member] - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Grants outstanding at beginning of the period	252,321	411,781	153,170
Shares, Granted		27,590	341,500
Shares, Vested	(100,840)	(187,050)	(63,264)
Shares, Cancelled	(15,356)		(19,625)
Shares, Grants outstanding at end of the period	136,125	252,321	411,781
Weighted Average Grant Date Fair Value per Share, Grants outstanding at beginning of the period	$ 42.37	$ 37.23	$ 34.53
Weighted Average Grant Date Fair Value per Share, Granted		98.57	34.58
Weighted Average Grant Date Fair Value per Share, Vested	40.54	39.34	14.60
Weighted Average Grant Date Fair Value per Share, Cancelled	48.94		43.02
Weighted Average Grant Date Fair Value per Share, Grants outstanding at end of the period	$ 42.98	$ 42.37	$ 37.23

Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units (RSUs) [Member] - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Grants outstanding at beginning of the period	251,298	66,552
Shares, Granted	511,283	230,736	181,029
Shares, Vested	(84,068)	(30,276)	(78,017)
Shares, Cancelled	(72,639)	(15,714)	(36,460)
Shares, Grants outstanding at end of the period	605,874	251,298	66,552
Weighted Average Grant Date Fair Value per Share, Grants outstanding at beginning of the period	$ 81.21	$ 33.72
Weighted Average Grant Date Fair Value per Share, Granted	131.18	87.95	$ 33.03
Weighted Average Grant Date Fair Value per Share, Vested	75.12	33.23	32.63
Weighted Average Grant Date Fair Value per Share, Cancelled	103.03	71.45	32.63
Weighted Average Grant Date Fair Value per Share, Grants outstanding at end of the period	$ 121.61	$ 81.21	$ 33.72

Summary of Stock Appreciation Rights Activity (Detail) - Stock Appreciation Rights [Member] - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares, Grants outstanding at beginning of the period	100,000	100,000	100,000
Shares, Exercised	(100,000)
Shares, Grants outstanding at end of the period		100,000	100,000
Shares, Grants exercisable at end of the period		100,000	100,000
Shares, Grants vested and expected to vest at end of the period		100,000	100,000
Weighted Average Exercise Price per Share, Grants outstanding at beginning of the period	$ 23.85	$ 23.85	$ 23.85
Weighted Average Exercise Price per Share, Exercised	$ (23.85)
Weighted Average Exercise Price per Share, Grants outstanding at end of the period		23.85	23.85
Weighted Average Exercise Price per Share, Grants exercisable at end of the period		23.85	23.85
Weighted Average Exercise Price per Share, Grants vested and expected to vest at end of the period		$ 23.85	$ 23.85

Summary of Employee Stock Purchase Plan Activity and Expense (Detail) - 2013 Employee Stock Purchase Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares purchased	92,086	75,094	102,698
Proceeds received (in millions)	$ 5.1	$ 2.3	$ 1.4

Summary of Stock-Based Compensation Expense by Function Included within Consolidated Statements of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 78,602	$ 50,127	$ 30,465
Research and Development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	27,681	14,214	8,542
Selling, General and Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 50,921	$ 35,913	$ 21,923

Summary of Stock-Based Compensation Expense by Grant Type Included within Consolidated Statements of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 78,602	$ 50,127	$ 30,465
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	53,427	37,671	23,416
Restricted Stock Awards/Units (RSAs/RSUs) [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	20,103	10,632	5,295
Employee Stock Purchase Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 5,072	$ 1,824	$ 1,754

401 (K) PLAN - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]
Expense related to 401 (K) Plan	$ 3.4	$ 2.1	$ 1.4
Defined contribution plan, employers matching contribution, service period				1 year
Defined contribution plan, employers matching contribution, vesting percentage after one years of service				100.00%
Description of 401(k) plan	The Company sponsors a 401(k) Plan (“the Plan”) in the U.S. and other retirement plans in the rest of the world, all of which are defined contribution plans. The Plan is available to all employees who are age 21 or older. Participants may make voluntary contributions and the Company makes matching contributions according to the Plan’s matching formula. Matching contributions fully vest after one year of service for all employees. The expense related to the Plan primarily consists of the Company’s matching contributions.
Age limit for eligibility to participate in the defined contribution plan	21 years

Summary of Other (Loss) Income (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Nonoperating Income Expense [Abstract]
Interest expense									$ (30,669)	$ (33,709)	$ (5,801)
Interest income									7,238	6,810	1,809
Amortization of investment discount									15,350	8,573	1,401
Other expense									(236)	(656)	601
Gain from sale of Priority Review Voucher											125,000
Total other (loss) income	$ (4,773)	$ (2,510)	$ (862)	$ (172)	$ (2,311)	$ (6,968)	$ (5,218)	$ (4,485)	$ (8,317)	$ (18,982)	$ 123,010

Summary of Loss before Provision for Income Taxes by Jurisdiction (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Domestic									$ (489,747)	$ (309,294)	$ (45,686)
Foreign									(224,133)	(53,316)	(2,942)
Loss before income tax expense (benefit)	$ (234,992)	$ (126,100)	$ (276,229)	$ (76,559)	$ (141,674)	$ (77,067)	$ (108,645)	$ (35,224)	$ (713,880)	$ (362,610)	$ (48,628)

Summary of Provision for Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current provision:
Federal										$ (110)	$ 204
State									$ 521	(653)	1,856
Foreign									1,050	311
Total current provision									1,571	(452)	2,060
Deferred benefit:
Federal									(15)
State									(5)
Foreign									(356)	(240)
Total deferred benefit									(376)	(240)
Total current provision	$ 711	$ 226	$ 174	$ 84	$ (779)	$ (674)	$ 622	$ 139	$ 1,195	$ (692)	$ 2,060

Reconciliation Between Effective Tax Rate and Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal income tax rate	21.00%	21.00%	34.00%
State taxes	6.30%	12.30%	(27.70%)
Research and development and other tax credits	3.30%	3.10%	8.50%
Valuation allowance	(16.80%)	(45.50%)	(93.20%)
Permanent differences	1.80%	6.90%	6.40%
Sarepta International C.V. return to provision		(0.10%)	62.10%
Impact of tax reform, net of valuation allowance			5.90%
Basis difference in subsidiary	(8.40%)
Foreign rate differential	(7.40%)	(0.90%)	(0.60%)
Other		3.40%	0.40%
Effective tax rate	(0.20%)	0.20%	(4.20%)

Income Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Feb. 28, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Net change in valuation allowance for deferred tax assets		$ 119,500,000	$ 164,800,000
Operating loss carryforwards, valuation allowance		7,900,000
Net operating loss carried forwards		304,033,000	212,342,000
Accrual for interest or penalties		$ 0	$ 0
Recognized interest and/or penalties				$ 0	$ 0
Minimum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year		2020
Maximum [Member]
Income Taxes [Line Items]
Operating loss carryforwards, ending of expiration year		2039
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 1,166,200,000
Net operating loss carryforwards subject to expiration		579,900,000
Net operating loss carried forwards		586,300,000
State [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		859,000,000.0
Net operating loss carryforwards subject to expiration		807,700,000
Net operating loss carried forwards		51,300,000
Foreign [Member] \| Sarepta International Holdings GmbH [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 8,000,000.0
Research and Development Credits [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Description		These federal and state research and development credits begin to expire between 2020 and 2039 and between 2020 and 2034, respectively.
Research and Development Credits [Member] \| Federal [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Amount		$ 74,700,000
Research and Development Credits [Member] \| Federal [Member] \| Minimum [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period		2020
Research and Development Credits [Member] \| Federal [Member] \| Maximum [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period		2039
Research and Development Credits [Member] \| State [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Amount		$ 34,100,000
Research and Development Credits [Member] \| State [Member] \| Minimum [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period		2020
Research and Development Credits [Member] \| State [Member] \| Maximum [Member]
Income Taxes [Line Items]
Research and development credits carryforward, Expiration period		2034
Warrant Agreement \| Myonexus Therapeutics, Inc. [Member]
Income Taxes [Line Items]
Accumulated costs related to acquisition	$ 253,700,000
Up-front and milestone payments	85,000,000.0
Exercise option	$ 168,700,000

Analysis of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 304,033	$ 212,342
Difference in depreciation and amortization	40,095	55,162
Research and development tax credits	103,806	67,309
Stock-based compensation	24,114	15,538
Lease liabilities	15,796	4,831
Deferred revenue	939	888
Capitalized inventory	18,255	22,943
Other	16,270	15,727
Total deferred tax assets	523,308	394,740
Deferred tax liabilities:
Right of use asset	(10,782)
Debt discount	(23,099)	(25,162)
Total deferred tax liabilities	(33,881)	(25,162)
Valuation allowance	(488,829)	(369,345)
Net deferred tax assets	$ 598	$ 233

Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Balance at beginning of the period	$ 37,544	$ 5,134	$ 4,644
Increase related to current year tax positions	4,275	2,164	735
Increase related to prior year tax positions	109	30,246
Decrease related to prior year tax positions	(175)		(245)
Balance at end of the period	$ 41,753	$ 37,544	$ 5,134

Leases - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Lessee Lease Description [Line Items]
Operating lease liabilities	$ 55,566	$ 60,100
Right-of-use assets	37,933	$ 42,500
ASU No. 2016-02 [Member]
Lessee Lease Description [Line Items]
Operating lease liabilities	60,100
Right-of-use assets	42,500
ASU No. 2016-02 [Member] \| Restatement Adjustment [Member]
Lessee Lease Description [Line Items]
De-recognition of deferred rent to reduce right-of-use assets	$ (18,000)

Summary of Lease Costs Recognized Under Topic 842 and Other Information Pertaining to Operating Leases (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Lease cost
Operating lease cost	$ 10,335
Variable lease cost	3,967
Total lease cost	14,302
Other information
Operating lease payments	$ 10,416
Weighted average remaining lease term	5 years 6 months
Weighted average discount rate	7.50%

Summary of Maturities of Lease Liabilities and Reconciliation of Lease Liabilities Recognized Under Topic 842 (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019
Maturity of lease liability
2020	$ 11,718
2021	12,891
2022	11,080
2023	11,230
2024	11,471
Thereafter	9,654
Total minimum lease payments	68,044
Less: imputed interest	(12,478)
Total operating lease liabilities	55,566	$ 60,100
Included in the condensed consolidated balance sheet:
Current portion of lease liabilities within other current liabilities	$ 7,846
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent
Lease liabilities	$ 47,720
Total operating lease liabilities	$ 55,566	$ 60,100

Summary of Aggregate Future Minimum Non-Cancellable Commitments under Leases (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Maturity of lease liability
2020	$ 11,395
2021	12,558
2022	10,757
2023	10,898
2024	11,128
Thereafter	9,396
Total minimum lease payments	$ 66,132

Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Net loss	$ (235,703)	$ (126,326)	$ (276,403)	$ (76,643)	$ (140,895)	$ (76,393)	$ (109,267)	$ (35,363)	$ (715,075)	$ (361,918)	$ (50,688)
Weighted-average common shares outstanding - basic									73,615	66,250	58,818
Weighted-average common shares outstanding - diluted									73,615	66,250	58,818
Net loss per share — basic and diluted	$ (3.16)	$ (1.70)	$ (3.74)	$ (1.07)	$ (2.05)	$ (1.15)	$ (1.67)	$ (0.55)	$ (9.71)	$ (5.46)	$ (0.86)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Basic and Diluted Net Loss Per Share (Parenthetical) (Detail) - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Nov. 14, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of net loss per share	9.1	9.1	9.4
2024 Convertible Notes [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Debt instrument, conversion price	$ 73.42			$ 73.42
Effect on diluted net earnings (loss) per share	$ 0

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 55
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-URI http://asc.fasb.org/extlink&oid=117327953&loc=d3e4984-109258

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 942
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-Subparagraph (SX 210.9-04(23))
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Commitments and Contingencies - Additional Information (Detail) $ in Millions	1 Months Ended			12 Months Ended
	May 31, 2019 USD ($)	Oct. 31, 2018 Suite	Jun. 30, 2018 USD ($) Payment Month Quarter	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($)
CRO [Member]
Commitments And Contingencies [Line Items]
Cancellable future commitments				$ 91.4
CRO [Member] \| Other Funding Commitments [Member]
Commitments And Contingencies [Line Items]
Expenditures incurred by CROs				31.6	$ 19.6	$ 13.9
Manufacturing Agreement [Member] \| Brammer [Member]
Commitments And Contingencies [Line Items]
Advance upfront fee to be paid on execution of agreements			$ 20.0
Number of non-refundable process equipment fee payments \| Payment			2
Required non refundable payments at each time of procurement of equipment					$ 5.0		$ 5.0
Quarterly capacity access fee payments			$ 10.0
Manufacturing Agreement [Member] \| Brammer [Member]
Commitments And Contingencies [Line Items]
Advance upfront fee to be paid on execution of agreements	$ 6.0
Quarterly capacity access fee payments	$ 13.3		$ 10.0
Supply agreement term			6 years
Successive renewal term of supply agreement			2 years
Minimum number of months prior to expiration of term for renewal \| Month			24
Maximum required additional quarters for remittance of capacity access fees before terminate agreement \| Quarter			8
Cash payment under agreements				75.5
Manufacturing Collaboration Agreement [Member] \| Paragon [Member]
Commitments And Contingencies [Line Items]
Number of dedicated clean room suites \| Suite		2
Number of additional clean room suites available on optional reserve \| Suite		2
Agreement expiration date		Dec. 31, 2024
Usage fees per annum per clean room suite				1.0
Manufacturing Collaboration Agreement [Member] \| Paragon [Member] \| Other Noncurrent Assets [Member]
Commitments And Contingencies [Line Items]
Clean room suite reservation fees payments				40.1
Manufacturing Collaboration Agreement [Member] \| Paragon [Member] \| Maximum [Member]
Commitments And Contingencies [Line Items]
Clean room suite reservation fees				$ 48.0
Percentage of credit on clean room use fee if threshold met				100.00%
Manufacturing Collaboration Agreement [Member]
Commitments And Contingencies [Line Items]
Pre-launch period purchase obligation, minimum amount per quarter per clean room				$ 4.0
Clinical and Commercial Supply Agreement [Member] \| Aldevron LLC [Member]
Commitments And Contingencies [Line Items]
Agreement expiration date				Dec. 31, 2019
Agreement expiration description				The Company exercised the option to extend the CCSA to December 31, 2020 (the “2020 Option”) and has another option to extend the term of the CCSA for an additional year to December 31, 2021 (the “2021 Renewal Right”).
Percentage of prepayments credited back equal to batch invoice amount				50.00%
Clinical and Commercial Supply Agreement [Member] \| Aldevron LLC [Member] \| Other Current Assets [Member]
Commitments And Contingencies [Line Items]
Prepayments to extend agreement term				$ 22.8
Clinical and Commercial Supply Agreement [Member] \| Aldevron LLC [Member] \| Maximum [Member]
Commitments And Contingencies [Line Items]
Advance upfront fee to be paid on execution of agreements				$ 20.0

Summary of Non-Cancelable Contractual Obligations Arising From Long-term Contractual Arrangements (Detail) $ in Thousands	Dec. 31, 2019 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2020	$ 378,744
2021	183,661
2022	64,653
2023	58,319
2024	58,309
Thereafter	149,350
Total manufacturing commitments	$ 893,036

Subsequent Event - Additional Information (Details) $ in Millions	Feb. 14, 2020 USD ($)
Subsequent Event \| F D A
Subsequent Event [Line Items]
Agreement to sell	$ 111.0

Financial Information by Quarter (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Product, net	$ 100,113	$ 99,041	$ 94,668	$ 87,011	$ 84,415	$ 78,486	$ 73,529	$ 64,604	$ 380,833	$ 301,034	$ 154,584
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Total revenues	$ 100,113	$ 99,041	$ 94,668	$ 87,011	$ 84,415	$ 78,486	$ 73,529	$ 64,604	$ 380,833	$ 301,034	$ 154,584
Cost and expenses:
Cost of sales (excluding amortization of in-licensed rights)	15,567	13,037	15,919	12,063	13,135	8,741	6,735	5,582	56,586	34,193	7,353
Research and development expense	223,141	133,949	113,266	90,553	146,207	86,584	122,848	46,204
Selling, general and administrative	81,424	75,429	67,393	60,566	64,220	53,044	47,156	43,341	284,812	207,761	122,682
Acquired in-process research and development			173,240						173,240
Settlement and license charges	10,000								10,000		28,427
Amortization of in-licensed rights	200	216	217	216	216	216	217	216	849	865	1,053
Total cost and expenses	330,332	222,631	370,035	163,398	223,778	148,585	176,956	95,343	1,086,396	644,662	326,222
Operating loss	(230,219)	(123,590)	(275,367)	(76,387)	(139,363)	(70,099)	(103,427)	(30,739)	(705,563)	(343,628)	(171,638)
Other (loss) income:
Other expense, net	(4,773)	(2,510)	(862)	(172)
Total other (loss) income	(4,773)	(2,510)	(862)	(172)	(2,311)	(6,968)	(5,218)	(4,485)	(8,317)	(18,982)	123,010
Interest expense and other, net					(2,311)	(6,968)	(5,218)	(4,485)
Loss before income tax expense (benefit)	(234,992)	(126,100)	(276,229)	(76,559)	(141,674)	(77,067)	(108,645)	(35,224)	(713,880)	(362,610)	(48,628)
Income tax expense (benefit)	711	226	174	84	(779)	(674)	622	139	1,195	(692)	2,060
Gain from sale of Priority Review Voucher											125,000
Net loss	$ (235,703)	$ (126,326)	$ (276,403)	$ (76,643)	$ (140,895)	$ (76,393)	$ (109,267)	$ (35,363)	$ (715,075)	$ (361,918)	$ (50,688)
Net loss per share — basic and diluted	$ (3.16)	$ (1.70)	$ (3.74)	$ (1.07)	$ (2.05)	$ (1.15)	$ (1.67)	$ (0.55)	$ (9.71)	$ (5.46)	$ (0.86)
Weighted average number of shares of common stock used in computing basic and diluted net loss per share	74,557	74,177	73,958	71,731	68,653	66,209	65,484	64,631	73,615,000	66,250,000	58,818,000