Sarepta Therapeutics (SRPT) 10-Q 7 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Aug. 02, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	SRPT
Entity Registrant Name	Sarepta Therapeutics, Inc.
Entity Central Index Key	0000873303
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		74,340,417
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-14895
Entity Tax Identification Number	930797222
Entity Address, Address Line One	215 First Street
Entity Address, Address Line Two	Suite 415
Entity Address, State or Province	MA
Entity Address, City or Town	Cambridge
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	274-4000

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 808,591	$ 370,829
Short-term investments	294,478	803,083
Accounts receivable	56,981	49,044
Inventory	156,569	125,445
Other current assets	110,799	77,782
Total current assets	1,427,418	1,426,183
Property and equipment, net of accumulated depreciation of $38,398 and $28,149 as of June 30, 2019, and December 31, 2018, respectively	117,201	97,024
Intangible assets, net of accumulated amortization of $4,685 and $3,852 as of June 30, 2019, and December 31, 2018, respectively	11,825	11,574
Right of use asset, net	39,449
Other assets	151,860	107,294
Total assets	1,747,753	1,642,075
Current liabilities:
Accounts payable	44,045	33,829
Accrued expenses	107,328	134,095
Deferred revenue	3,303	3,303
Other current liabilities	7,413	2,463
Total current liabilities	162,089	173,690
Long-term debt	431,040	420,554
Lease liabilities	50,209
Deferred rent and other	5,248	15,555
Total liabilities	648,586	609,799
Commitments and contingencies (Note 14)
Stockholders’ equity:
Preferred stock, $0.0001 par value, 3,333,333 shares authorized; none issued and outstanding
Common stock, $0.0001 par value, 99,000,000 shares authorized; 74,327,767 and 71,071,887 issued and outstanding at June 30, 2019, and December 31, 2018, respectively	7	7
Additional paid-in capital	3,031,050	2,611,294
Accumulated other comprehensive income (loss)	82	(99)
Accumulated deficit	(1,931,972)	(1,578,926)
Total stockholders’ equity	1,099,167	1,032,276
Total liabilities and stockholders’ equity	$ 1,747,753	$ 1,642,075

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Property and equipment, accumulated depreciation	$ 38,398	$ 28,149
Intangible assets, accumulated amortization	$ 4,685	$ 3,852
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	74,327,767	71,071,887
Common stock, outstanding	74,327,767	71,071,887

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues:
Product, net	$ 94,668	$ 73,529	$ 181,679	$ 138,133
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Total revenues	$ 94,668	$ 73,529	$ 181,679	$ 138,133
Cost and expenses:
Cost of sales (excluding amortization of in-licensed rights)	15,919	6,735	27,982	12,317
Research and development	113,266	122,848	203,819	169,052
Selling, general and administrative	67,393	47,156	127,959	90,497
Acquired in-process research and development	173,240		173,240
Amortization of in-licensed rights	217	217	433	433
Total cost and expenses	370,035	176,956	533,433	272,299
Operating loss	(275,367)	(103,427)	(351,754)	(134,166)
Other loss:
Other expense, net	(862)	(5,218)	(1,034)	(9,703)
Other loss	(862)	(5,218)	(1,034)	(9,703)
Loss before income tax expense	(276,229)	(108,645)	(352,788)	(143,869)
Income tax expense	174	622	258	761
Net loss	(276,403)	(109,267)	(353,046)	(144,630)
Other comprehensive income:
Unrealized gains on investments	63	282	181	18
Total other comprehensive income	63	282	181	18
Comprehensive loss	$ (276,340)	$ (108,985)	$ (352,865)	$ (144,612)
Net loss per share - basic and diluted	$ (3.74)	$ (1.67)	$ (4.85)	$ (2.22)
Weighted average number of shares of common stock used in computing basic and diluted net loss per share	73,958	65,484	72,850	65,060

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 789,217	$ 6	$ 2,006,598	$ (379)	$ (1,217,008)
Balance (in shares) at Dec. 31, 2017		64,792
Exercise of options for common stock	11,888	$ 1	11,887
Exercise of options for common stock, shares		653
Grant of restricted stock awards and vest of restricted stock units, net of cancellations, shares		14
Issuance of common stock under employee stock purchase plan	756		756
Issuance of common stock under employee stock purchase plan, shares		34
Stock-based compensation	10,526		10,526
Unrealized gains (losses) from available-for-sale securities	(264)			(264)
Net loss	(35,363)				(35,363)
Balance at Mar. 31, 2018	776,760	$ 7	2,029,767	(643)	(1,252,371)
Balance (in shares) at Mar. 31, 2018		65,493
Balance at Dec. 31, 2017	789,217	$ 6	2,006,598	(379)	(1,217,008)
Balance (in shares) at Dec. 31, 2017		64,792
Net loss	(144,630)
Balance at Jun. 30, 2018	699,047	$ 7	2,061,039	(361)	(1,361,638)
Balance (in shares) at Jun. 30, 2018		66,346
Balance at Mar. 31, 2018	776,760	$ 7	2,029,767	(643)	(1,252,371)
Balance (in shares) at Mar. 31, 2018		65,493
Exercise of options for common stock	21,743		21,743
Exercise of options for common stock, shares		872
Grant of restricted stock awards and vest of restricted stock units, net of cancellations, shares		26
Shares withheld for taxes	(5,750)		(5,750)
Shares withheld for taxes, shares		(45)
Stock-based compensation	15,279		15,279
Unrealized gains (losses) from available-for-sale securities	282			282
Net loss	(109,267)				(109,267)
Balance at Jun. 30, 2018	699,047	$ 7	2,061,039	(361)	(1,361,638)
Balance (in shares) at Jun. 30, 2018		66,346
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
Exercise of options for common stock	9,973		9,973
Exercise of options for common stock, shares		382
Grant of restricted stock awards and vest of restricted stock units, net of cancellations, shares		35
Shares withheld for taxes	(889)		(889)
Shares withheld for taxes, shares		(7)
Issuance of common stock for cash, net of offering costs	365,264		365,264
Issuance of common stock for cash, net of offering costs, shares		2,604
Issuance of common stock under employee stock purchase plan	2,326		2,326
Issuance of common stock under employee stock purchase plan, shares		48
Stock-based compensation	16,139		16,139
Unrealized gains (losses) from available-for-sale securities	118			118
Net loss	(76,643)				(76,643)
Balance at Mar. 31, 2019	1,348,564	$ 7	3,004,107	19	(1,655,569)
Balance (in shares) at Mar. 31, 2019		74,134
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
Net loss	(353,046)
Balance at Jun. 30, 2019	1,099,167	$ 7	3,031,050	82	(1,931,972)
Balance (in shares) at Jun. 30, 2019		74,328
Balance at Mar. 31, 2019	1,348,564	$ 7	3,004,107	19	(1,655,569)
Balance (in shares) at Mar. 31, 2019		74,134
Exercise of options for common stock	7,092		7,092
Exercise of options for common stock, shares		176
Grant of restricted stock awards and vest of restricted stock units, net of cancellations, shares		18
Issuance of common stock for cash, net of offering costs	89		89
Stock-based compensation	19,762		19,762
Unrealized gains (losses) from available-for-sale securities	63			63
Net loss	(276,403)				(276,403)
Balance at Jun. 30, 2019	$ 1,099,167	$ 7	$ 3,031,050	$ 82	$ (1,931,972)
Balance (in shares) at Jun. 30, 2019		74,328

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows $ in Thousands	6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)
Cash flows from operating activities:
Net loss	$ (353,046)	$ (144,630)
Adjustments to reconcile net loss to cash flows from operating activities:
Acquired in-process research and development	173,240
Depreciation and amortization	14,064	5,125
Amortization of investment discount	(5,800)	(2,828)
Non-cash interest expense	10,513	9,958
Stock-based compensation	35,901	25,805
Other	892	37
Changes in operating assets and liabilities, net:
Net increase in accounts receivable	(7,937)	(13,517)
Net increase in inventory	(31,124)	(20,521)
Net increase in other assets	(87,708)	(29,866)
Net increase in accounts payable, accrued expenses, deferred revenue and other liabilities	25,768	17,515
Net cash used in operating activities	(225,237)	(152,922)
Cash flows from investing activities:
Purchase of property and equipment	(32,945)	(20,863)
Purchase of intangible assets	(1,454)	(1,556)
Purchase of available-for-sale securities	(731,288)	(295,823)
Purchases of restricted investment		(353)
Maturity and sale of available-for-sale securities	1,225,847	249,243
Net cash provided by (used in) investing activities	287,604	(69,352)
Cash flows from financing activities:
Proceeds from revolving line of credit		173,354
Repayment of revolving line of credit		(173,653)
Repayments on mortgage loans		(1,265)
Proceeds from sale of common stock, net of offering costs	365,353
Taxes paid related to net share settlement of equity awards	(889)
Proceeds from exercise of stock options and purchase of stock under the Employee Stock Purchase Program	19,391	34,386
Net cash provided by financing activities	383,855	32,822
Increase (decrease) in cash, cash equivalents and restricted cash	446,222	(189,452)
Cash, cash equivalents and restricted cash:
Beginning of period	370,829	599,827
End of period	817,051	410,375
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	808,591	$ 410,375
Restricted cash in other assets	$ 8,460
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash	$ 817,051	$ 410,375
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	4,275	6,058
Supplemental schedule of non-cash investing activities and financing activities:
Sale of available-for-sale securities included in investment receivable	20,000
Reclassification of long term investments to short term investments		9,980
Intangible assets included in accrued expenses	226	294
Accrual for debt issuance costs related to the term loans		600
Property and equipment included in accrued expenses	2,902	$ 289
Myonexus Therapeutics, Inc. [Member]
Cash flows from investing activities:
Acquisition of Myonexus Therapeutics, Inc., net of cash acquired	$ (172,556)

ORGANIZATION AND NATURE OF BUSI

ORGANIZATION AND NATURE OF BUSINESS	6 Months Ended
	Jun. 30, 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 the discovery and development of unique RNA-targeted therapeutics, gene therapy and other genetic medicine approaches for the treatment of rare diseases. Applying its proprietary, highly-differentiated and innovative platform technologies, the Company is able to target a broad range of diseases and disorders. Its first commercial product in the U.S., EXONDYS 51 ® As of June 30, 2019, the Company had approximately $1,112.6 million of cash, cash equivalents and investments, consisting of $808.6 million of cash and cash equivalents, $294.5 million of short-term investments, and $9.5 million of restricted cash and investments. The Company believes that its balance of cash, cash equivalents and investments as of the date of the issuance of this report is sufficient to fund its current operational plan for at least the next twelve months, though it may pursue raising 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 ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENT ACCOUNTING PRONOUNCEMENTS	6 Months Ended
	Jun. 30, 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 unaudited condensed consolidated financial statements, which have been prepared in accordance with accounting principles generally accepted in the United States (“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: discovering, developing, manufacturing and delivering therapies to patients with rare diseases. These unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and related notes for the year ended December 31, 2018 which are contained in the Company’s Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission on February 28, 2019. The results for the three and six months ended June 30, 2019 are not necessarily indicative of the results to be expected for the full year. Estimates and Uncertainties The preparation of the unaudited condensed 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. Concentration of Credit Risk Financial instruments which potentially subject the Company to concentrations of credit risk consist of accounts receivable from customers, cash held at financial institutions and cash equivalents and investments. As of June 30, 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 30 to 61 days. Outside of the U.S., the payment terms range between 30 and 150 days. Three individual customers accounted for 43%, 43% and 12% of net product revenues for the three months ended June 30, 2019 and 42%, 41% and 14% of net product revenues for the six months ended June 30, 2019. Three individual customers accounted for 44%, 35% and 20% of net product revenues for the three months ended June 30, 2018 and 44%, 35% and 19% of net product revenues for the six months ended June 30, 2018. Three individual customers accounted for 51%, 27% and 14% of accounts receivable from product sales as of June 30, 2019 and 61%, 26% and 11% of accounts receivable from product sales as of June 30, 2018. 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 profile. As of June 30, 2019, the Company believes that such customers are of high credit quality. As of June 30, 2019 the Company’s cash w as concentrated at three financial institution s in the U.S. , which potentially exposes the Company to credit risks. However, the Company does not believe that there is significant risk of non-performance by the financial institution s . Significant Accounting Policies For details about the Company’s accounting policies, please read Note 2, Summary of Significant Accounting Policies and Recent Accounting Pronouncements Leases Effective January 1, 2019, the Company adopted ASC Topic 842, Leases (“ASC 842”), using the required 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 and June 30, 2019. 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 material leases 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. 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 entities with a practical expedient that allows them to make an accounting policy election to not separate lease and non-lease components by class of underlying asset. In using this expedient, entities would account for each lease component and the related non-lease component together as a single component. For new and amended leases beginning after January 1, 2019, 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. There have not been any other material changes to the Company’s accounting policies through June 30, 2019. Recent Accounting Pronouncements In August 2018, the Financial Accounting Standards Board (the “FASB”) issued ASU No. 2018-13, “Fair Value Measurement (Topic 820), Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement”. 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 arrange is ready for its intended use. ASU No. 2018-15 will be effective for fiscal years be ginning after December 15, 2019 with early adoption permitted. As of June 30, 2019 , the Company has not elected to early adopt this guidance but does not expect that the ad option of this guidance will 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” be effective for fiscal years beginning after December 15, 2019 with early adoption permitted

LICENSE AND COLLABORATION AGREE

LICENSE AND COLLABORATION AGREEMENTS	6 Months Ended
	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
LICENSE AND COLLABORATION AGREEMENTS	3. LICENSE AND COLLABORATION AGREEMENTS Myonexus Therapeutics On May 3, 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. 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. The following table summarizes the total consideration for the acquisition and the value of assets acquired and liability assumed: Consideration Purchase price $ 165,000 Transactions costs and other fees 8,753 Contingent consideration 4,500 Total consideration $ 178,253 Assets Acquired 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 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 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 June 30, 2019, the sales milestone was not probable of being achieved and, therefore, no assets or expense were recognized. Milestone Obligations The Company has license and collaboration agreements in place for which it could be obligated to pay, in addition to the payment of up-front fees upon execution of the agreements, certain milestone payments as a product candidate proceeds from the submission of an investigational new drug application through approval for commercial sale and beyond. As of June 30, 2019, the Company may be obligated to make up to $1,146.3 million of future development, regulatory, commercial, and up-front royalty milestone payments associated with its license and collaboration agreements. For the three and six months ended June 30, 2019, the Company recognized up-front and milestone payments of $14.4 million and $15.5 million, respectively, as research and development expense in the accompanying unaudited condensed consolidated statement of operations and comprehensive loss, with no such activity for the three and six months ended June 30, 2018.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	4. FAIR VALUE MEASUREMENTS The Company has certain financial assets and liabilities 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 tables below present information about the Company’s financial assets and liabilities that are measured and carried at fair value and indicate the level within the fair value hierarchy of valuation techniques it utilizes to determine such fair value: Fair Value Measurement as of June 30, 2019 Total Level 1 Level 2 Level 3 (in thousands) Assets Money market funds $ 181,040 $ 181,040 $ — $ — Commercial paper 87,370 — 87,370 — Government and government agency bonds 677,242 677,242 — — Corporate bonds 19,982 19,982 — — Strategic equity investments 32,154 2,154 — 30,000 Certificates of deposit 1,001 1,001 — — Total assets $ 998,789 $ 881,419 $ 87,370 $ 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, the Company’s strategic investment in Lysogene S.A. and certificates of deposit. Certain of the government and government agency bonds are traded fixed income securities and are presented as cash equivalents on the unaudited condensed consolidated balance sheets as of June 30, 2019. The Company’s assets with fair value categorized as Level 2 within the fair value hierarchy consist of commercial paper. 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 asset with fair value categorized as Level 3 within the fair value hierarchy consists of a strategic investment in Series A preferred stock of Lacerta Therapeutics, Inc. (“Lacerta”) as more fully described in Note 3, License and Collaboration Agreements 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. The carrying amounts reported in the unaudited condensed consolidated balance sheets for cash and cash equivalents, accounts receivable, accounts payable, and revolving line of credit approximated fair value because of the immediate or short-term maturity of these financial instruments. The carrying amounts for the term loan approximated fair value based on market activity for other debt instruments with similar characteristics and comparable risk.

CASH, CASH EQUIVALENTS AND MARK

CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES	6 Months Ended
	Jun. 30, 2019
Cash And Cash Equivalents [Abstract]
CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES	5. CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES The following table summarizes the Company’s financial assets with maturities of less than 90 days from the date of purchase included in cash equivalents in the unaudited condensed consolidated balance sheets for each of the periods indicated: As of June 30, 2019 As of December 31, 2018 (in thousands) Money market funds $ 181,040 $ 42,920 Government and government agency bonds 452,506 111,587 Commercial paper 37,610 14,940 Total $ 671,156 $ 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 June 30, 2019 and December 31, 2018 was approximately two months. The following tables summarize the Company’s cash, cash equivalents and short-term investments for each of the periods indicated: As of June 30, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Cash and money market funds $ 318,475 $ — $ — $ 318,475 Commercial paper 87,370 — — 87,370 Government and government agency bonds 677,166 91 (15 ) 677,242 Corporate bonds 19,976 6 — 19,982 Total cash, cash equivalents and short-term investments $ 1,102,987 $ 97 $ (15 ) $ 1,103,069 As reported: Cash and cash equivalents $ 808,562 $ 34 $ (5 ) $ 808,591 Short-term investments 294,425 63 (10 ) 294,478 Total cash, cash equivalents and short-term investments $ 1,102,987 $ 97 $ (15 ) $ 1,103,069 As of December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair 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 short-term 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 short-term investments $ 1,174,011 $ 12 $ (111 ) $ 1,173,912

ACCOUNTS RECEIVABLE AND RESERVE

ACCOUNTS RECEIVABLE AND RESERVES FOR PRODUCT SALES	6 Months Ended
	Jun. 30, 2019
Receivables Net Current [Abstract]
ACCOUNTS RECEIVABLE AND RESERVES FOR PRODUCT SALES	6. 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 June 30, 2019 As of December 31, 2018 (in thousands) Product sales, net of discounts and allowances $ 56,189 $ 48,252 Government contract receivables 792 792 Total accounts receivable, net $ 56,981 $ 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, 2018 $ 1,378 $ 24,276 $ 538 $ 2,318 $ 28,510 Provision 4,874 21,004 2,240 2,233 30,351 Payments/credits (4,712 ) (15,002 ) (1,909 ) (2,854 ) (24,477 ) Balance, as of June 30, 2019 $ 1,540 $ 30,278 $ 869 $ 1,697 $ 34,384 The following table summarizes the total reserves above included in the Company’s unaudited condensed consolidated balance sheets for the periods indicated: As of June 30, 2019 As of December 31, 2018 (in thousands) Reduction to accounts receivable $ 3,563 $ 2,364 Component of accrued expenses 30,821 26,146 Total reserves $ 34,384 $ 28,510

INVENTORY

INVENTORY	6 Months Ended
	Jun. 30, 2019
Inventory Disclosure [Abstract]
INVENTORY	7. INVENTORY The following table summarizes the components of the Company’s inventory for the period indicated: As of June 30, 2019 As of December 31, 2018 (in thousands) Raw materials $ 72,126 $ 71,313 Work in progress 78,354 47,279 Finished goods 6,089 6,853 Total inventory $ 156,569 $ 125,445

OTHER CURRENT ASSETS AND OTHER

OTHER CURRENT ASSETS AND OTHER NON-CURRENT ASSETS	6 Months Ended
	Jun. 30, 2019
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
OTHER CURRENT ASSETS AND OTHER NON-CURRENT ASSETS	8. OTHER CURRENT ASSETS AND OTHER NON-CURRENT ASSETS The following table summarizes the Company’s other current assets for each of the periods indicated: As of June 30, 2019 As of December 31, 2018 (in thousands) Manufacturing-related deposits and prepaids $ 48,094 $ 39,036 Investment receivable 20,000 — Leasehold improvement receivable 13,474 13,474 Prepaid clinical and pre-clinical expenses 9,504 9,706 Payroll tax receivable 4,025 471 Prepaid maintenance services 3,343 2,994 Prepaid research expenses 2,519 1,932 Prepaid income tax 2,125 2,130 Prepaid commercial expenses 1,788 1,573 Other 5,927 6,466 Total other current assets $ 110,799 $ 77,782 The following table summarizes the Company’s other non-current assets for each of the periods indicated: As of June 30, 2019 As of December 31, 2018 (in thousands) Manufacturing-related deposits and prepaids $ 97,381 $ 62,821 Strategic investments 32,154 31,739 Restricted cash and investments 9,461 1,001 Prepaid clinical expenses 7,161 7,541 Alternative minimum tax credit 3,367 3,367 Other 2,336 825 Total other non-current assets $ 151,860 $ 107,294

ACCRUED EXPENSES

ACCRUED EXPENSES	6 Months Ended
	Jun. 30, 2019
Payables And Accruals [Abstract]
ACCRUED EXPENSES	9. ACCRUED EXPENSES The following table summarizes the Company’s accrued expenses for each of the periods indicated: As of June 30, 2019 As of December 31, 2018 (in thousands) Product revenue related reserves $ 30,821 $ 26,146 Accrued employee compensation costs 23,205 24,692 Accrued clinical and pre-clinical costs 15,706 11,396 Accrued contract manufacturing costs 12,699 15,794 Accrued professional fees 8,963 11,319 Accrued royalties 5,819 8,254 Accrued property and equipment 2,902 5,421 Accrued research costs 1,733 1,070 Accrued interest expense 1,045 1,045 Accrued collaboration cost sharing 541 2,167 Accrued milestone expense 492 24,020 Other 3,402 2,771 Total accrued expenses $ 107,328 $ 134,095

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
STOCK-BASED COMPENSATION	10. STOCK-BASED COMPENSATION The following table summarizes the Company’s stock awards granted for each of the periods indicated: For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Stock options 155,265 $ 67.80 528,096 $ 45.45 1,145,499 $ 75.27 1,652,681 $ 37.71 Restricted stock units 81,000 $ 121.34 18,695 $ 95.38 405,630 $ 138.79 169,420 $ 74.09 Restricted stock awards — $ — — $ — — $ — 17,090 $ 71.45 Stock-based Compensation Expense For the three months ended June 30, 2019 and 2018, total stock-based compensation expense was $19.8 million and $15.3 million, respectively. For the six months ended June 30, 2019 and 2018, total stock-based compensation expense was $35.9 million and $25.8 million, respectively. The increase in stock-based compensation expense for the three and six months was primarily driven by increases in awards associated with growth in employees and the increased value of such awards. The following table summarizes stock-based compensation expense by function included within the unaudited condensed consolidated statements of operations and comprehensive loss: For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 (in thousands) Research and development $ 6,923 $ 5,029 $ 12,010 $ 7,089 Selling, general and administrative 12,839 10,250 23,891 18,716 Total stock-based compensation expense $ 19,762 $ 15,279 $ 35,901 $ 25,805 The following table summarizes stock-based compensation expense by grant type included within the unaudited condensed consolidated statements of operations and comprehensive loss: For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 (in thousands) Stock options $ 13,777 $ 9,382 $ 25,234 $ 18,355 Restricted stock awards/units 5,184 5,407 9,100 6,667 Employee stock purchase plan 801 490 1,567 783 Total stock-based compensation expense $ 19,762 $ 15,279 $ 35,901 $ 25,805

OTHER EXPENSE, NET

OTHER EXPENSE, NET	6 Months Ended
	Jun. 30, 2019
Other Income And Expenses [Abstract]
OTHER EXPENSE, NET	11. OTHER EXPENSE, NET The following table summarizes other expense, net, for the periods indicated: For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 (in thousand) (in thousand) Interest expense $ (7,426 ) $ (8,145 ) $ (14,761 ) $ (15,779 ) Interest income 2,104 1,887 4,465 3,759 Amortization of investment discount 4,581 1,569 8,913 2,828 Other (expense) income (121 ) (529 ) 349 (511 ) Total other expense, net $ (862 ) $ (5,218 ) $ (1,034 ) $ (9,703 )

LEASES

LEASES	6 Months Ended
	Jun. 30, 2019
Leases [Abstract]
LEASES	12. LEASES The Company’s operating leases for its Cambridge, Andover and Burlington, Massachusetts and Dublin and Columbus, Ohio facilities provide for scheduled annual rent increases throughout each lease’s term. A summary of these leases are as follows: In June 2013, the Company entered into a lease agreement (the “Cambridge Lease”) for its headquarters located in Cambridge, Massachusetts. In April and September 2018 and June 2019, the Company entered into the seventh, eighth, and ninth amendment, respectively, to its Cambridge Lease which extended the original term of the lease to September 30, 2025 and increased the total rental space to approximately 170,929 square feet. In March and July of 2018, the Company entered into sublease agreements in Andover, Massachusetts, to lease a total of 23,102 square feet of office and lab space. These subleases expire in December 2020. In November 2018, the Company entered into a sublease agreement in Burlington, Massachusetts, to lease 44,740 square feet of office and lab space. The sublease expires in January 2022. In December 2018, the Company entered into lease agreements in Dublin and Columbus, Ohio, to lease 22,600 square feet and 77,679 square feet, respectively, of office and lab space. The leases expire in November 2019 and June 2026, respectively. 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. Further, the Company reclassified upon adoption $18.0 million of deferred rent which served to reduce the ROU assets recognized on the balance sheet, in accordance with the transition guidance. As of June 30, 2019, operating lease assets were $39.4 million and operating lease liabilities were $57.4 million. Amounts related to financing leases were immaterial. The following table contains a summary of the lease costs recognized under Topic 842 and other information pertaining to the Company’s operating leases for the three and six months ended June 30, 2019: Operating Lease (in thousands) For the three months ended June 30, 2019 For the six months ended June 30, 2019 Lease cost Operating lease cost 2,530 5,132 Variable lease cost 809 1,938 Total lease cost $ 3,339 $ 7,070 Other information Operating lease payments 4,816 Operating lease liabilities arising from obtaining ROU assets — Weighted average remaining lease term 5.9 years Weighted average discount rate 7.50 % Future minimum lease payments under the Company’s non-cancelable operating leases as of June 30, 2019, are as follows: Maturity of lease liability (in thousands) As of June 30, 2019 2019 (July - December) $ 5,467 2020 11,395 2021 12,558 2022 10,737 2023 10,877 Thereafter 20,484 Total minimum lease payments 71,518 Less: imputed interest (14,148 ) Total operating lease liabilities $ 57,370 Included in the condensed consolidated balance sheet: Current portion of lease liabilities within other current liabilities $ 7,161 Lease liabilities 50,209 Total operating lease liabilities $ 57,370 Future minimum lease payments under the Company’s non-cancelable operating leases as of December 31, 2018, are as follows: Maturity of lease liability (in thousands) As of December 31, 2018 2019 $ 11,588 2020 11,395 2021 12,558 2022 10,757 2023 10,898 Thereafter 20,524 Total minimum lease payments $ 77,720

NET LOSS PER SHARE

NET LOSS PER SHARE	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
NET LOSS PER SHARE	13. 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. For the three and six months ended June 30, 2019 and 2018, there were no differences between basic and diluted net loss per share since the effect of common stock equivalents would be anti-dilutive due to the net loss position and, therefore, would be excluded from the diluted net loss per share calculation. For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 (in thousands, except per share amounts) Net loss $ (276,403 ) $ (109,267 ) $ (353,046 ) $ (144,630 ) Weighted-average common shares outstanding - basic 73,958 65,484 72,850 65,060 Effect of dilutive securities* — — — — Weighted-average common shares outstanding - diluted 73,958 65,484 72,850 65,060 Net loss per share - basic and diluted $ (3.74 ) $ (1.67 ) $ (4.85 ) $ (2.22 ) * For the three and six months ended June 30, 2019 and 2018, stock options, RSAs, RSUs, stock appreciation rights (“SAR”) to purchase 9.7 million and 9.4 million shares of the Company’s common stock, respectively, were excluded from the diluted net loss per share calculation as their effect would have been anti-dilutive.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	6 Months Ended
	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	14. COMMITMENTS AND CONTINGENCIES Manufacturing Obligations 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 Brammer Manufacturing Agreement (collectively, “Brammer Supply Agreements”) with Brammer Bio MA, LLC (“Brammer”) in June 2018 and May 2019, respectively. 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. For more information related to the Brammer Manufacturing Agreement, please read Note 21, Commitments and Contingencies 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 will be in effect as Brammer works towards achieving full capacity at its facility. Upon execution of the Amendment, the Company determined that the Brammer Supply Agreement s 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 does not control the facility or related equipment during construction and, thus, the lease does not fall in the scope of “build-to-suit” accounting. The lease has not commenced as of June 30, 2019. Accordingly, total cumulative payments made to Brammer of $ 55.0 million have been recorded as other assets and will be considered in the initial measurement of the cost of the right-of-use asset at the lease commencement date. Paragon Bioservices, Inc. In October 2018, the Company entered into a manufacturing collaboration agreement (the “Collaboration Agreement”) with Paragon Bioservices, Inc. (“Paragon”). Pursuant to the terms of the Collaboration Agreement, 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. On February 22, 2019, the Company entered into a manufacturing and supply agreement (the “Paragon Supply Agreement”) with Paragon. The Paragon Supply Agreement consists of 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 batches 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. Both the Collaboration Agreement and the Supply Agreements will expire on December 31, 2024 The following table summarizes the aggregate non-cancelable contractual obligations arising from the Company’s manufacturing obligations: As of June 30, 2019 (in thousands) 2019 (July - December) $ 147,352 2020 194,195 2021 55,990 2022 55,204 2023 55,244 Thereafter 161,001 Total manufacturing commitments $ 668,986 Additionally, should the Company obtain regulatory approval for any drug product candidate produced as a part of the Company’s manufacturing obligations above, it may be subject to additional minimum batch requirements with the respective manufacturing parties. 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. As of June 30, 2019, there are no such material legal claims, actions or complaints where the Company is named.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENT ACCOUNTING PRONOUNCEMENTS (Policies)	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements, which have been prepared in accordance with accounting principles generally accepted in the United States (“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: discovering, developing, manufacturing and delivering therapies to patients with rare diseases. These unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and related notes for the year ended December 31, 2018 which are contained in the Company’s Annual Report on Form 10-K filed with the U.S. Securities and Exchange Commission on February 28, 2019. The results for the three and six months ended June 30, 2019 are not necessarily indicative of the results to be expected for the full year.
Estimates and Uncertainties	Estimates and Uncertainties The preparation of the unaudited condensed 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.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments which potentially subject the Company to concentrations of credit risk consist of accounts receivable from customers, cash held at financial institutions and cash equivalents and investments. As of June 30, 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 30 to 61 days. Outside of the U.S., the payment terms range between 30 and 150 days. Three individual customers accounted for 43%, 43% and 12% of net product revenues for the three months ended June 30, 2019 and 42%, 41% and 14% of net product revenues for the six months ended June 30, 2019. Three individual customers accounted for 44%, 35% and 20% of net product revenues for the three months ended June 30, 2018 and 44%, 35% and 19% of net product revenues for the six months ended June 30, 2018. Three individual customers accounted for 51%, 27% and 14% of accounts receivable from product sales as of June 30, 2019 and 61%, 26% and 11% of accounts receivable from product sales as of June 30, 2018. 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 profile. As of June 30, 2019, the Company believes that such customers are of high credit quality. As of June 30, 2019 the Company’s cash w as concentrated at three financial institution s in the U.S. , which potentially exposes the Company to credit risks. However, the Company does not believe that there is significant risk of non-performance by the financial institution s .
Leases	Leases Effective January 1, 2019, the Company adopted ASC Topic 842, Leases (“ASC 842”), using the required 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 and June 30, 2019. 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 material leases 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. 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 entities with a practical expedient that allows them to make an accounting policy election to not separate lease and non-lease components by class of underlying asset. In using this expedient, entities would account for each lease component and the related non-lease component together as a single component. For new and amended leases beginning after January 1, 2019, 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. There have not been any other material changes to the Company’s accounting policies through June 30, 2019.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In August 2018, the Financial Accounting Standards Board (the “FASB”) issued ASU No. 2018-13, “Fair Value Measurement (Topic 820), Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement”. 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 arrange is ready for its intended use. ASU No. 2018-15 will be effective for fiscal years be ginning after December 15, 2019 with early adoption permitted. As of June 30, 2019 , the Company has not elected to early adopt this guidance but does not expect that the ad option of this guidance will 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” be effective for fiscal years beginning after December 15, 2019 with early adoption permitted

LICENSE AND COLLABORATION AGR_2

LICENSE AND COLLABORATION AGREEMENTS (Tables)	6 Months Ended
	Jun. 30, 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 acquisition and the value of assets acquired and liability assumed: Consideration Purchase price $ 165,000 Transactions costs and other fees 8,753 Contingent consideration 4,500 Total consideration $ 178,253 Assets Acquired 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

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured and Carried at Fair Value	The tables below present information about the Company’s financial assets and liabilities that are measured and carried at fair value and indicate the level within the fair value hierarchy of valuation techniques it utilizes to determine such fair value: Fair Value Measurement as of June 30, 2019 Total Level 1 Level 2 Level 3 (in thousands) Assets Money market funds $ 181,040 $ 181,040 $ — $ — Commercial paper 87,370 — 87,370 — Government and government agency bonds 677,242 677,242 — — Corporate bonds 19,982 19,982 — — Strategic equity investments 32,154 2,154 — 30,000 Certificates of deposit 1,001 1,001 — — Total assets $ 998,789 $ 881,419 $ 87,370 $ 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

CASH, CASH EQUIVALENTS AND MA_2

CASH, CASH EQUIVALENTS AND MARKETABLE SECURITIES (Tables)	6 Months Ended
	Jun. 30, 2019
Cash And Cash Equivalents [Abstract]
Summary of Company Financial Assets with Maturities of Less Than 90 Days Included in Cash Equivalents	The following table summarizes the Company’s financial assets with maturities of less than 90 days from the date of purchase included in cash equivalents in the unaudited condensed consolidated balance sheets for each of the periods indicated: As of June 30, 2019 As of December 31, 2018 (in thousands) Money market funds $ 181,040 $ 42,920 Government and government agency bonds 452,506 111,587 Commercial paper 37,610 14,940 Total $ 671,156 $ 169,447
Summary of Company Cash, Cash Equivalents and Short-Term Investments	The following tables summarize the Company’s cash, cash equivalents and short-term investments for each of the periods indicated: As of June 30, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Cash and money market funds $ 318,475 $ — $ — $ 318,475 Commercial paper 87,370 — — 87,370 Government and government agency bonds 677,166 91 (15 ) 677,242 Corporate bonds 19,976 6 — 19,982 Total cash, cash equivalents and short-term investments $ 1,102,987 $ 97 $ (15 ) $ 1,103,069 As reported: Cash and cash equivalents $ 808,562 $ 34 $ (5 ) $ 808,591 Short-term investments 294,425 63 (10 ) 294,478 Total cash, cash equivalents and short-term investments $ 1,102,987 $ 97 $ (15 ) $ 1,103,069 As of December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair 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 short-term 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 short-term investments $ 1,174,011 $ 12 $ (111 ) $ 1,173,912

ACCOUNTS RECEIVABLE AND RESER_2

ACCOUNTS RECEIVABLE AND RESERVES FOR PRODUCT SALES (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2019 As of December 31, 2018 (in thousands) Product sales, net of discounts and allowances $ 56,189 $ 48,252 Government contract receivables 792 792 Total accounts receivable, net $ 56,981 $ 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, 2018 $ 1,378 $ 24,276 $ 538 $ 2,318 $ 28,510 Provision 4,874 21,004 2,240 2,233 30,351 Payments/credits (4,712 ) (15,002 ) (1,909 ) (2,854 ) (24,477 ) Balance, as of June 30, 2019 $ 1,540 $ 30,278 $ 869 $ 1,697 $ 34,384
Summary of Total Reserves Included in Consolidated Balance Sheets	The following table summarizes the total reserves above included in the Company’s unaudited condensed consolidated balance sheets for the periods indicated: As of June 30, 2019 As of December 31, 2018 (in thousands) Reduction to accounts receivable $ 3,563 $ 2,364 Component of accrued expenses 30,821 26,146 Total reserves $ 34,384 $ 28,510

INVENTORY (Tables)

INVENTORY (Tables)	6 Months Ended
	Jun. 30, 2019
Inventory Disclosure [Abstract]
Summary of Components of Inventory	The following table summarizes the components of the Company’s inventory for the period indicated: As of June 30, 2019 As of December 31, 2018 (in thousands) Raw materials $ 72,126 $ 71,313 Work in progress 78,354 47,279 Finished goods 6,089 6,853 Total inventory $ 156,569 $ 125,445

OTHER CURRENT ASSETS AND OTHE_2

OTHER CURRENT ASSETS AND OTHER NON-CURRENT ASSETS (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2019 As of December 31, 2018 (in thousands) Manufacturing-related deposits and prepaids $ 48,094 $ 39,036 Investment receivable 20,000 — Leasehold improvement receivable 13,474 13,474 Prepaid clinical and pre-clinical expenses 9,504 9,706 Payroll tax receivable 4,025 471 Prepaid maintenance services 3,343 2,994 Prepaid research expenses 2,519 1,932 Prepaid income tax 2,125 2,130 Prepaid commercial expenses 1,788 1,573 Other 5,927 6,466 Total other current assets $ 110,799 $ 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 June 30, 2019 As of December 31, 2018 (in thousands) Manufacturing-related deposits and prepaids $ 97,381 $ 62,821 Strategic investments 32,154 31,739 Restricted cash and investments 9,461 1,001 Prepaid clinical expenses 7,161 7,541 Alternative minimum tax credit 3,367 3,367 Other 2,336 825 Total other non-current assets $ 151,860 $ 107,294

ACCRUED EXPENSES (Tables)

ACCRUED EXPENSES (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2019 As of December 31, 2018 (in thousands) Product revenue related reserves $ 30,821 $ 26,146 Accrued employee compensation costs 23,205 24,692 Accrued clinical and pre-clinical costs 15,706 11,396 Accrued contract manufacturing costs 12,699 15,794 Accrued professional fees 8,963 11,319 Accrued royalties 5,819 8,254 Accrued property and equipment 2,902 5,421 Accrued research costs 1,733 1,070 Accrued interest expense 1,045 1,045 Accrued collaboration cost sharing 541 2,167 Accrued milestone expense 492 24,020 Other 3,402 2,771 Total accrued expenses $ 107,328 $ 134,095

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Awards Granted	The following table summarizes the Company’s stock awards granted for each of the periods indicated: For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Stock options 155,265 $ 67.80 528,096 $ 45.45 1,145,499 $ 75.27 1,652,681 $ 37.71 Restricted stock units 81,000 $ 121.34 18,695 $ 95.38 405,630 $ 138.79 169,420 $ 74.09 Restricted stock awards — $ — — $ — — $ — 17,090 $ 71.45
Summary of Stock-Based Compensation Expense by Function Included within Condensed Consolidated Statements of Operations and Comprehensive Loss	The following table summarizes stock-based compensation expense by function included within the unaudited condensed consolidated statements of operations and comprehensive loss: For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 (in thousands) Research and development $ 6,923 $ 5,029 $ 12,010 $ 7,089 Selling, general and administrative 12,839 10,250 23,891 18,716 Total stock-based compensation expense $ 19,762 $ 15,279 $ 35,901 $ 25,805
Summary of Stock-Based Compensation Expense by Grant Type Included within Condensed Consolidated Statements of Operations and Comprehensive Loss	The following table summarizes stock-based compensation expense by grant type included within the unaudited condensed consolidated statements of operations and comprehensive loss: For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 (in thousands) Stock options $ 13,777 $ 9,382 $ 25,234 $ 18,355 Restricted stock awards/units 5,184 5,407 9,100 6,667 Employee stock purchase plan 801 490 1,567 783 Total stock-based compensation expense $ 19,762 $ 15,279 $ 35,901 $ 25,805

OTHER EXPENSE, NET (Tables)

OTHER EXPENSE, NET (Tables)	6 Months Ended
	Jun. 30, 2019
Other Income And Expenses [Abstract]
Summary of Other Expense, Net	The following table summarizes other expense, net, for the periods indicated: For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 (in thousand) (in thousand) Interest expense $ (7,426 ) $ (8,145 ) $ (14,761 ) $ (15,779 ) Interest income 2,104 1,887 4,465 3,759 Amortization of investment discount 4,581 1,569 8,913 2,828 Other (expense) income (121 ) (529 ) 349 (511 ) Total other expense, net $ (862 ) $ (5,218 ) $ (1,034 ) $ (9,703 )

LEASES (Tables)

LEASES (Tables)	6 Months Ended
	Jun. 30, 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 Topic 842 and other information pertaining to the Company’s operating leases for the three and six months ended June 30, 2019: Operating Lease (in thousands) For the three months ended June 30, 2019 For the six months ended June 30, 2019 Lease cost Operating lease cost 2,530 5,132 Variable lease cost 809 1,938 Total lease cost $ 3,339 $ 7,070 Other information Operating lease payments 4,816 Operating lease liabilities arising from obtaining ROU assets — Weighted average remaining lease term 5.9 years Weighted average discount rate 7.50 %
Summary of Future Minimum Lease Payments Under Non-Cancelable Operating Leases Recognized Under Topic 842	Future minimum lease payments under the Company’s non-cancelable operating leases as of June 30, 2019, are as follows: Maturity of lease liability (in thousands) As of June 30, 2019 2019 (July - December) $ 5,467 2020 11,395 2021 12,558 2022 10,737 2023 10,877 Thereafter 20,484 Total minimum lease payments 71,518 Less: imputed interest (14,148 ) Total operating lease liabilities $ 57,370 Included in the condensed consolidated balance sheet: Current portion of lease liabilities within other current liabilities $ 7,161 Lease liabilities 50,209 Total operating lease liabilities $ 57,370
Summary of Future Minimum Lease Payments Under Non-Cancelable Operating Leases	Future minimum lease payments under the Company’s non-cancelable operating leases as of December 31, 2018, are as follows: Maturity of lease liability (in thousands) As of December 31, 2018 2019 $ 11,588 2020 11,395 2021 12,558 2022 10,757 2023 10,898 Thereafter 20,524 Total minimum lease payments $ 77,720

NET LOSS PER SHARE (Tables)

NET LOSS PER SHARE (Tables)	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Basic and Diluted Net Loss Per Share	For the three and six months ended June 30, 2019 and 2018, there were no differences between basic and diluted net loss per share since the effect of common stock equivalents would be anti-dilutive due to the net loss position and, therefore, would be excluded from the diluted net loss per share calculation. For the Three Months Ended June 30, For the Six Months Ended June 30, 2019 2018 2019 2018 (in thousands, except per share amounts) Net loss $ (276,403 ) $ (109,267 ) $ (353,046 ) $ (144,630 ) Weighted-average common shares outstanding - basic 73,958 65,484 72,850 65,060 Effect of dilutive securities* — — — — Weighted-average common shares outstanding - diluted 73,958 65,484 72,850 65,060 Net loss per share - basic and diluted $ (3.74 ) $ (1.67 ) $ (4.85 ) $ (2.22 ) * For the three and six months ended June 30, 2019 and 2018, stock options, RSAs, RSUs, stock appreciation rights (“SAR”) to purchase 9.7 million and 9.4 million shares of the Company’s common stock, respectively, were excluded from the diluted net loss per share calculation as their effect would have been anti-dilutive.

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	6 Months Ended
	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Summary of Aggregate Non-Cancelable Contractual Obligations Arising from Manufacturing Obligations	The following table summarizes the aggregate non-cancelable contractual obligations arising from the Company’s manufacturing obligations: As of June 30, 2019 (in thousands) 2019 (July - December) $ 147,352 2020 194,195 2021 55,990 2022 55,204 2023 55,244 Thereafter 161,001 Total manufacturing commitments $ 668,986

Organization and Nature of Bu_2

Organization and Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Cash, cash equivalents and investments	$ 1,112,600
Cash and cash equivalents	808,591	$ 370,829	$ 410,375
Short-term investments	294,478	803,083
Restricted cash and investments	$ 9,461	$ 1,001

Summary of Significant Accoun_3

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2018	Jun. 30, 2019USD ($)Segment	Jun. 30, 2018	Jan. 01, 2019USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment			1
Right-of-use assets	$ 39,449		$ 39,449
Operating lease liabilities	57,370		57,370
ASU No. 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Right-of-use assets	42,500		42,500		$ 42,500
Operating lease liabilities	$ 60,100		$ 60,100		$ 60,100
Product Revenues [Member] | Customer One [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	43.00%	44.00%	42.00%	44.00%
Product Revenues [Member] | Customer Two [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	43.00%	35.00%	41.00%	35.00%
Product Revenues [Member] | Customer Three [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	12.00%	20.00%	14.00%	19.00%
Accounts Receivable [Member] | Customer One [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage			51.00%	61.00%
Accounts Receivable [Member] | Customer Two [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage			27.00%	26.00%
Accounts Receivable [Member] | Customer Three [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage			14.00%	11.00%
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable payment term			30 days
Minimum [Member] | Outside of U.S. [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable payment term			30 days
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable payment term			61 days
Maximum [Member] | Outside of U.S. [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable payment term			150 days

License and Collaboration Agr_3

License and Collaboration Agreements - Additional Information (Detail) - USD ($) $ in Thousands	Apr. 04, 2019	Feb. 27, 2019	May 03, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent consideration liability of acquisition				$ 5,200		$ 5,200
Myonexus Therapeutics, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Final exercise price		$ 165,000
Additional transaction fees		8,800		165,000		165,000
Additional development milestone payments to be paid		$ 200,000
Date of acquisition	Apr. 4, 2019
Contingent consideration liability of acquisition				4,500		4,500
Warrant Agreement [Member] | Myonexus Therapeutics, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front cash payment under agreements			$ 60,000
Cash consideration under agreement excluding contingent payments			$ 200,000
License and Collaboration Agreements [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development milestone and up-front payments recognized as research and development expense				14,400	$ 0	15,500	$ 0
License and Collaboration Agreements [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory, commercial milestone and up-front royalty payments				$ 1,146,300		$ 1,146,300

License and Collaboration Agr_4

License and Collaboration Agreements - Schedule of Total Consideration of Business Acquisition (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Feb. 27, 2019
Consideration
Contingent consideration	$ 5,200	$ 5,200
Assets Acquired
In-process research and development	173,240	173,240
Myonexus Therapeutics, Inc. [Member]
Consideration
Purchase price	165,000	165,000	$ 8,800
Transactions costs and other fees		8,753
Contingent consideration	4,500	4,500
Total consideration		178,253
Assets Acquired
Cash and cash equivalents	1,197	1,197
Prepaids	3,816	3,816
In-process research and development		173,240
Total assets acquired	178,253	178,253
Liability Assumed
Contingent consideration	4,500	4,500
Total liability assumed	$ 4,500	$ 4,500

Assets and Liabilities Measured

Assets and Liabilities Measured and Carried at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 998,789	$ 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	181,040	42,920
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	87,370	125,907
Government and Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	677,242	760,235
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	19,982	43,468
Strategic Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	32,154	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
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	881,419	849,363
Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	181,040	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	677,242	760,235
Level 1 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	19,982	43,468
Level 1 [Member] | Strategic Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	2,154	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 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	87,370	125,907
Level 2 [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	87,370	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 As

Summary of Company Financial Assets with Maturities of Less Than 90 Days Included in Cash Equivalents (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash equivalents	$ 671,156	$ 169,447
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash equivalents	181,040	42,920
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash equivalents	452,506	111,587
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Cash equivalents	$ 37,610	$ 14,940

Cash, Cash Equivalents and Ma_3

Cash, Cash Equivalents and Marketable Securities - Additional Information (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 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 E

Summary of Company Cash, Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	$ 808,562	$ 370,827
Cash and cash equivalents, Gross unrealized gains	34	3
Cash and cash equivalents, Gross unrealized losses	(5)	(1)
Cash and cash equivalents	808,591	370,829	$ 410,375
Cash, cash equivalents and short-term investments, Amortized cost	1,102,987	1,174,011
Cash, cash equivalents and short-term investments, Gross unrealized gains	97	12
Cash, cash equivalents and short-term investments, Gross unrealized losses	(15)	(111)
Cash, cash equivalents and short-term investments, Fair value	1,103,069	1,173,912
Available for sale debt securities current, Amortized cost	294,425	803,184
Available for sale debt securities current, Gross unrealized gains	63	9
Available for sale debt securities current, Gross unrealized losses	(10)	(110)
Available for sale debt securities current, Fair value	294,478	803,083
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	318,475	244,302
Cash and cash equivalents	318,475	244,302
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost	87,370	125,907
Available for sale debt securities, Fair value	87,370	125,907
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost	677,166	760,258
Available for sale debt securities, Gross unrealized gains	91	12
Available for sale debt securities, Gross unrealized losses	(15)	(35)
Available for sale debt securities, Fair value	677,242	760,235
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost	19,976	43,544
Available for sale debt securities, Gross unrealized gains	6
Available for sale debt securities, Gross unrealized losses		(76)
Available for sale debt securities, Fair value	$ 19,982	$ 43,468

Summary of Components of Accoun

Summary of Components of Accounts Receivable (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Receivables Net Current [Abstract]
Product sales, net of discounts and allowances	$ 56,189	$ 48,252
Government contract receivables	792	792
Total accounts receivable, net	$ 56,981	$ 49,044

Summary of Change in Reserves f

Summary of Change in Reserves for Discounts and Allowances (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2019USD ($)
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	$ 28,510
Provision	30,351
Payments/credits	(24,477)
Balance, as of June 30, 2019	34,384
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	1,378
Provision	4,874
Payments/credits	(4,712)
Balance, as of June 30, 2019	1,540
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	24,276
Provision	21,004
Payments/credits	(15,002)
Balance, as of June 30, 2019	30,278
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	538
Provision	2,240
Payments/credits	(1,909)
Balance, as of June 30, 2019	869
Other Accruals [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	2,318
Provision	2,233
Payments/credits	(2,854)
Balance, as of June 30, 2019	$ 1,697

Summary of Total Reserves Inclu

Summary of Total Reserves Included in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Receivables Net Current [Abstract]
Reduction to accounts receivable	$ 3,563	$ 2,364
Component of accrued expenses	30,821	26,146
Total reserves	$ 34,384	$ 28,510

Summary of Components of Invent

Summary of Components of Inventory (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 72,126	$ 71,313
Work in progress	78,354	47,279
Finished goods	6,089	6,853
Total inventory	$ 156,569	$ 125,445

Summary of Other Current Assets

Summary of Other Current Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Prepaid Expense And Other Assets Current [Abstract]
Manufacturing-related deposits and prepaids	$ 48,094	$ 39,036
Investment receivable	20,000
Leasehold improvement receivable	13,474	13,474
Prepaid clinical and pre-clinical expenses	9,504	9,706
Payroll tax receivable	4,025	471
Prepaid maintenance services	3,343	2,994
Prepaid research expenses	2,519	1,932
Prepaid income tax	2,125	2,130
Prepaid commercial expenses	1,788	1,573
Other	5,927	6,466
Total other current assets	$ 110,799	$ 77,782

Summary of Other Non-current As

Summary of Other Non-current Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Prepaid Expense And Other Assets Noncurrent [Abstract]
Manufacturing-related deposits and prepaids	$ 97,381	$ 62,821
Strategic investments	32,154	31,739
Restricted cash and investments	9,461	1,001
Prepaid clinical expenses	7,161	7,541
Alternative minimum tax credit	3,367	3,367
Other	2,336	825
Total other non-current assets	$ 151,860	$ 107,294

Summary of Accrued Expenses (De

Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Product revenue related reserves	$ 30,821	$ 26,146
Accrued employee compensation costs	23,205	24,692
Accrued clinical and pre-clinical costs	15,706	11,396
Accrued contract manufacturing costs	12,699	15,794
Accrued professional fees	8,963	11,319
Accrued royalties	5,819	8,254
Accrued property and equipment	2,902	5,421
Accrued research costs	1,733	1,070
Accrued interest expense	1,045	1,045
Accrued collaboration cost sharing	541	2,167
Accrued milestone expense	492	24,020
Other	3,402	2,771
Total accrued expenses	$ 107,328	$ 134,095

Summary of Stock Awards Granted

Summary of Stock Awards Granted (Detail) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants, Stock options	155,265	528,096	1,145,499	1,652,681
Weighted Average Grant Date Fair Value, Stock options	$ 67.80	$ 45.45	$ 75.27	$ 37.71
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants, Restricted stock units and awards	81,000	18,695	405,630	169,420
Weighted Average Grant Date Fair Value, Restricted stock units and awards	$ 121.34	$ 95.38	$ 138.79	$ 74.09
Restricted Stock Awards (RSAs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants, Restricted stock units and awards				17,090
Weighted Average Grant Date Fair Value, Restricted stock units and awards				$ 71.45

Stock Based Compensation - Addi

Stock Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-based compensation expense	$ 19,762	$ 15,279	$ 35,901	$ 25,805

Summary of Stock-Based Compensa

Summary of Stock-Based Compensation Expense by Function Included within Condensed Consolidated Statements of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 19,762	$ 15,279	$ 35,901	$ 25,805
Research and Development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	6,923	5,029	12,010	7,089
Selling, General and Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 12,839	$ 10,250	$ 23,891	$ 18,716

Summary of Stock-Based Compen_2

Summary of Stock-Based Compensation Expense by Grant Type Included within Condensed Consolidated Statements of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 19,762	$ 15,279	$ 35,901	$ 25,805
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	13,777	9,382	25,234	18,355
Restricted Stock Awards/Units (RSAs/RSUs) [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	5,184	5,407	9,100	6,667
Employee Stock Purchase Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 801	$ 490	$ 1,567	$ 783

Summary of Other Expense, Net (

Summary of Other Expense, Net (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Nonoperating Income Expense [Abstract]
Interest expense	$ (7,426)	$ (8,145)	$ (14,761)	$ (15,779)
Interest income	2,104	1,887	4,465	3,759
Amortization of investment discount	4,581	1,569	8,913	2,828
Other (expense) income	(121)	(529)	349	(511)
Other loss	$ (862)	$ (5,218)	$ (1,034)	$ (9,703)

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2019USD ($)ft²	Jan. 01, 2019USD ($)
Lessee Lease Description [Line Items]
Operating lease liabilities | $	$ 57,370
Right-of-use assets | $	39,449
ASU No. 2016-02 [Member]
Lessee Lease Description [Line Items]
Operating lease liabilities | $	60,100	$ 60,100
Right-of-use assets | $	42,500	$ 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)
Dublin [Member]
Lessee Lease Description [Line Items]
Office and lab Space on lease | ft²	22,600
Lease expiration date	2019-11
Lease agreement entered date	2018-12
Columbus [Member]
Lessee Lease Description [Line Items]
Office and lab Space on lease | ft²	77,679
Lease expiration date	2026-06
Lease agreement entered date	2018-12
Sublease [Member] | Andover [Member]
Lessee Lease Description [Line Items]
Office and lab Space on lease | ft²	23,102
Lease agreement entered date description	March and July of 2018
Lease expiration date	2020-12
Sublease [Member] | Burlington [Member]
Lessee Lease Description [Line Items]
Office and lab Space on lease | ft²	44,740
Lease expiration date	2022-01
Lease agreement entered date	2018-11
Lease Agreements [Member]
Lessee Lease Description [Line Items]
Lease expiration date	Sep. 30, 2025
Existence of option to extend operating lease [true false]	true
Total rental space | ft²	170,929

Summary of Lease Costs Recogniz

Summary of Lease Costs Recognized Under Topic 842 and Other Information Pertaining to Operating Leases (Detail) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019USD ($)	Jun. 30, 2019USD ($)
Lease cost
Operating lease cost	$ 2,530	$ 5,132
Variable lease cost	809	1,938
Total lease cost	$ 3,339	7,070
Other information
Operating lease payments		$ 4,816
Weighted average remaining lease term	5 years 10 months 24 days	5 years 10 months 24 days
Weighted average discount rate	7.50%	7.50%

Summary of Future Minimum Lease

Summary of Future Minimum Lease Payments Under Non-Cancelable Operating Leases Recognized Under Topic 842 (Detail) $ in Thousands	Jun. 30, 2019USD ($)
Maturity of lease liability
2019 (July - December)	$ 5,467
2020	11,395
2021	12,558
2022	10,737
2023	10,877
Thereafter	20,484
Total minimum lease payments	71,518
Less: imputed interest	(14,148)
Total operating lease liabilities	57,370
Included in the condensed consolidated balance sheet:
Current portion of lease liabilities within other current liabilities	$ 7,161
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent
Lease liabilities	$ 50,209
Total operating lease liabilities	$ 57,370

Summary of Future Minimum Lea_2

Summary of Future Minimum Lease Payments Under Non-Cancelable Operating Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Maturity of lease liability
2019	$ 11,588
2020	11,395
2021	12,558
2022	10,757
2023	10,898
Thereafter	20,524
Total minimum lease payments	$ 77,720

Basic and Diluted Net Loss Per

Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net loss		$ (276,403)	$ (76,643)	$ (109,267)	$ (35,363)	$ (353,046)	$ (144,630)
Weighted-average common shares outstanding - basic		73,958		65,484		72,850	65,060
Effect of dilutive securities*	[1]	0		0		0	0
Weighted-average common shares outstanding - diluted		73,958		65,484		72,850	65,060
Net loss per share - basic and diluted		$ (3.74)		$ (1.67)		$ (4.85)	$ (2.22)
[1]	For the three and six months ended June 30, 2019 and 2018, stock options, RSAs, RSUs, stock appreciation rights (“SAR”) to purchase 9.7 million and 9.4 million shares of the Company’s common stock, respectively, were excluded from the diluted net loss per share calculation as their effect would have been anti-dilutive.

Basic and Diluted Net Loss Pe_2

Basic and Diluted Net Loss Per Share (Parenthetical) (Detail) - shares shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Anti-dilutive securities excluded from computation of net loss per share	9.7	9.4	9.7	9.4

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	Feb. 22, 2019USD ($)	May 31, 2019USD ($)	Oct. 31, 2018Suite	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)
Manufacturing Agreement [Member] | Brammer [Member]
Commitments And Contingencies [Line Items]
Advance upfront fee to be paid on execution of amendment		$ 6
Quarterly capacity access fee payments		$ 13.3		$ 10
Cash payment under agreements					$ 55
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
Manufacturing Supply Agreement [Member] | Paragon [Member]
Commitments And Contingencies [Line Items]
Pre-launch period purchase obligation, minimum amount per quarter per clean room	$ 4
Agreement expiration date	Dec. 31, 2024

Summary of Aggregate Non-Cancel

Summary of Aggregate Non-Cancelable Contractual Obligations Arising from Manufacturing Obligations (Detail) - Manufacturing Supply Agreement [Member] - Paragon [Member] $ in Thousands	Jun. 30, 2019USD ($)
Commitments And Contingencies [Line Items]
2019 (July - December)	$ 147,352
2020	194,195
2021	55,990
2022	55,204
2023	55,244
Thereafter	161,001
Total manufacturing commitments	$ 668,986