Sarepta Therapeutics (SRPT) 10-Q 8 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 03, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
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		74,153,868

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 732,190	$ 370,829
Short-term investments	612,018	803,083
Accounts receivable	50,510	49,044
Inventory	140,467	125,445
Other current assets	136,238	77,782
Total current assets	1,671,423	1,426,183
Property and equipment, net of accumulated depreciation of $32,612 and $28,149 as of March 31, 2019, and December 31, 2018, respectively	106,280	97,024
Intangible assets, net of accumulated amortization of $4,276 and $3,852 as of March 31, 2019, and December 31, 2018, respectively	11,781	11,574
Right of use asset, net of accumulated amortization of $1,491 and nil as of March 31, 2019 and December 31, 2018, respectively	41,098
Other assets	133,313	107,294
Total assets	1,963,895	1,642,075
Current liabilities:
Accounts payable	26,499	33,829
Accrued expenses	100,120	134,095
Deferred revenue	3,985	3,303
Other current liabilities	6,762	2,463
Total current liabilities	137,366	173,690
Long-term debt	425,752	420,554
Lease liabilities	52,165
Deferred rent and other	48	15,555
Total liabilities	615,331	609,799
Commitments and contingencies (Note 15)
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; 74,133,521 and 71,071,887 issued and outstanding at March 31, 2019, and December 31, 2018, respectively	7	7
Additional paid-in capital	3,004,107	2,611,294
Accumulated other comprehensive income (loss)	19	(99)
Accumulated deficit	(1,655,569)	(1,578,926)
Total stockholders’ equity	1,348,564	1,032,276
Total liabilities and stockholders’ equity	$ 1,963,895	$ 1,642,075

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Property and equipment, accumulated depreciation	$ 32,612	$ 28,149
Intangible assets, accumulated amortization	4,276	$ 3,852
Right of use asset, accumulated amortization	$ 1,491
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	74,133,521	71,071,887
Common stock, outstanding	74,133,521	71,071,887

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues:
Product, net	$ 87,011	$ 64,604
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember
Total revenues	$ 87,011	$ 64,604
Cost and expenses:
Cost of sales (excluding amortization of in-licensed rights)	12,063	5,582
Research and development	90,553	46,204
Selling, general and administrative	60,566	43,341
Amortization of in-licensed rights	216	216
Total cost and expenses	163,398	95,343
Operating loss	(76,387)	(30,739)
Other loss:
Interest expense and other, net	(172)	(4,485)
Other loss	(172)	(4,485)
Loss before income tax expense	(76,559)	(35,224)
Income tax expense	84	139
Net loss	(76,643)	(35,363)
Other comprehensive income (loss):
Unrealized gain (loss) on cash equivalents and short-term investments	118	(264)
Total other comprehensive income (loss)	118	(264)
Comprehensive loss	$ (76,525)	$ (35,627)
Net loss per share - basic and diluted	$ (1.07)	$ (0.55)
Weighted average number of shares of common stock used in computing basic and diluted net loss per share	71,731	64,631

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 [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 gain (loss) from cash equivalents and 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, 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 gain (loss) from cash equivalents and 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

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (76,643)	$ (35,363)
Adjustments to reconcile net loss to cash flows from operating activities:
Depreciation and amortization	6,370	2,252
Amortization of investment discount	(3,476)	(1,259)
Non-cash interest expense	5,208	4,940
Loss on disposal of assets	88	10
Stock-based compensation	16,139	10,526
Changes in operating assets and liabilities, net:
Net increase in accounts receivable	(1,466)	(10,380)
Net increase in inventory	(15,022)	(15,770)
Net (increase) decrease in other assets	(79,564)	4,672
Net decrease in accounts payable, accrued expenses, deferred revenue and other liabilities	2,133	4,704
Net cash used in operating activities	(146,233)	(35,668)
Cash flows from investing activities:
Purchase of property and equipment	(16,263)	(12,166)
Purchase of intangible assets	(855)	(673)
Purchase of available-for-sale securities	(494,481)	(91,514)
Maturity and sale of available-for-sale securities	646,830	90,093
Net cash provided by (used in) investing activities	135,231	(14,260)
Cash flows from financing activities:
Proceeds from revolving line of credit		96,235
Repayment of revolving line of credit		(100,142)
Repayments on mortgage loans		(1,265)
Proceeds from sale of common stock, net of offering costs	365,264
Proceeds from exercise of stock options and purchase of stock under the Employee Stock Purchase Program	12,299	12,643
Net cash provided by financing activities	377,563	7,471
Increase (decrease) in cash, cash equivalents and restricted cash	366,561	(42,457)
Cash, cash equivalents and restricted cash:
Beginning of period	370,829	599,827
End of period	737,390	557,370
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	732,190	557,234
Restricted cash in other assets	$ 5,200	$ 136
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash	$ 737,390	$ 557,370
Supplemental disclosure of cash flow information:
Cash paid during the period for interest		853
Supplemental schedule of non-cash investing activities and financing activities:
Shares withheld for taxes	889
Sale of available-for-sale securities included in investment receivable	42,300
Reclassification of long term investments to short term investments		9,980
Intangible assets included in accrued expenses	230	202
Property and equipment included in accrued expenses	$ 2,878	$ 2,980

ORGANIZATION AND NATURE OF BUSI

ORGANIZATION AND NATURE OF BUSINESS	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
ORGANIZATION AND NATURE OF BUSINESS	1. ORGANIZATION AND NATURE OF BUSINESS Sarepta Therapeutics, Inc. (together with its wholly-owned subsidiaries, “Sarepta” or the “Company”) is a commercial-stage biopharmaceutical company focused on 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 March 31, 2019, the Company had approximately $1,350.4 million of cash, cash equivalents and investments, consisting of $732.2 million of cash and cash equivalents, $612.0 million of short-term investments, and $6.2 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 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	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENT ACCOUNTING PRONOUNCEMENTS	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENT ACCOUNTING PRONOUNCEMENTS Basis of Presentation The accompanying 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 months ended March 31, 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 and cash, cash equivalents and investments held at financial institutions. As of March 31, 2019, the majority of the Company’s accounts receivable arose from product sales in the U.S. and all customers have standard payment terms which generally require payment within 30 to 61 days. Outside of the U.S., the payment terms range between 30 and 150 days. Three individual customers accounted for 41%, 40% and 15% of net product revenues for the three months ended March 31, 2019 and 57%, 26% and 8% of accounts receivable from product sales as of March 31, 2019. 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 March 31, 2019, the Company believes that such customers are of high credit quality. As of March 31, 2019 the Company’s cash equivalents and investments were concentrated at three financial institutions 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 institutions. 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 the cumulative impact 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 balances 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 March 31, 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 expense 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 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 classes of all underlying assets and will allocate the contract consideration to the lease component only. There have not been any other material changes to the Company’s accounting policies as of March 31, 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”. .

LICENSE AND COLLABORATION AGREE

LICENSE AND COLLABORATION AGREEMENTS	3 Months Ended
	Mar. 31, 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 associated with the exercise of approximately $8.7 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 milestones. The acquisition was completed on April 4, 2019. As a result, the Company is expected to recognize approximately $168.7 million in in-process research and development expense during the three months ended June 30, 2019. 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 March 31, 2019, the Company may be obligated to make up to $555.8 million of future development, regulatory, commercial, and up-front royalty milestone payments associated with its license and collaboration agreements. For the three months ended March 31, 2019, the Company recognized milestone payments of $1.1 million as research and development expense in the accompanying unaudited condensed consolidated statement of operations and comprehensive loss, with no such activity for the three months ended March 31, 2018.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	4. FAIR VALUE MEASUREMENTS The Company has certain financial assets that are recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements. • Level 1 — quoted prices for identical instruments in active markets; • Level 2 — quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-derived valuations in which all significant inputs and significant value drivers are observable in active markets; and • Level 3 — valuations derived from valuation techniques in which one or more significant value drivers are unobservable. The tables below present information about the Company’s financial assets that are measured and carried at fair value and indicate the level within the fair value hierarchy of valuation techniques it utilizes to determine such fair value: Fair Value Measurement as of March 31, 2019 Total Level 1 Level 2 Level 3 (in thousands) Assets Money market funds $ 155,406 $ 155,406 $ — $ — Commercial paper 65,779 — 65,779 — Government and government agency bonds 807,025 807,025 — — Corporate bonds 33,582 33,582 — — Strategic equity investments 32,359 2,359 — 30,000 Certificates of deposit 1,001 1,001 — — Total $ 1,095,152 $ 999,373 $ 65,779 $ 30,000 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 publically traded fixed income securities and are presented as cash equivalents on the unaudited condensed consolidated balance sheets as of March 31, 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 assets with fair value categorized as Level 3 within the fair value hierarchy consists of a strategic investment in Series A preferred stock of Lacerta Therapeutics, Inc. (“Lacerta”) as more fully described in 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	3 Months Ended
	Mar. 31, 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 March 31, 2019 As of December 31, 2018 (in thousands) Money market funds $ 155,406 $ 42,920 Government and government agency bonds 294,368 111,587 Commercial paper — 14,940 Total $ 449,774 $ 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 March 31, 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 March 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value (in thousands) Cash and money market funds $ 437,822 $ — $ — $ 437,822 Commercial paper 65,779 — — $ 65,779 Government and government agency bonds 807,001 31 (7 ) $ 807,025 Corporate bonds 33,587 — (5 ) $ 33,582 Total cash, cash equivalents and investments $ 1,344,189 $ 31 $ (12 ) $ 1,344,208 As reported: Cash and cash equivalents $ 732,179 $ 11 $ — $ 732,190 Short-term investments 612,010 20 (12 ) $ 612,018 Total cash, cash equivalents and investments $ 1,344,189 $ 31 $ (12 ) $ 1,344,208 As of December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value (in thousands) Cash and money market funds $ 244,302 $ — $ — $ 244,302 Commercial paper 125,907 — — 125,907 Government and government agency bonds 760,258 12 (35 ) 760,235 Corporate bonds 43,544 — (76 ) 43,468 Total cash, cash equivalents and investments $ 1,174,011 $ 12 $ (111 ) $ 1,173,912 As reported: Cash and cash equivalents $ 370,827 $ 3 $ (1 ) $ 370,829 Short-term investments 803,184 9 (110 ) 803,083 Total cash, cash equivalents and investments $ 1,174,011 $ 12 $ (111 ) $ 1,173,912

ACCOUNTS RECEIVABLE AND RESERVE

ACCOUNTS RECEIVABLE AND RESERVES FOR PRODUCT SALES	3 Months Ended
	Mar. 31, 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 March 31, 2019 As of December 31, 2018 (in thousands) Product sales, net of discounts and allowances $ 49,718 $ 48,252 Government contract receivables 792 792 Total accounts receivable, net $ 50,510 $ 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 2,566 9,429 936 1,064 13,995 Payments/credits (3,049 ) (5,191 ) (791 ) (2,015 ) (11,046 ) Balance, as of March 31, 2019 $ 895 $ 28,514 $ 683 $ 1,367 $ 31,459 The following table summarizes the total reserves above included in the Company’s unaudited condensed consolidated balance sheets for the periods indicated: As of March 31, 2019 As of December 31, 2018 (in thousands) Reduction to accounts receivable $ 2,405 $ 2,364 Component of accrued expenses 29,054 26,146 Total reserves $ 31,459 $ 28,510

INVENTORY

INVENTORY	3 Months Ended
	Mar. 31, 2019
Inventory Disclosure [Abstract]
INVENTORY	7. INVENTORY The following table summarizes the components of the Company’s inventory for the period indicated: As of March 31, 2019 As of December 31, 2018 (in thousands) Raw materials $ 70,271 $ 71,313 Work in progress 66,884 47,279 Finished goods 3,312 6,853 Total inventory $ 140,467 $ 125,445

OTHER CURRENT ASSETS AND OTHER

OTHER CURRENT ASSETS AND OTHER NON-CURRENT ASSETS	3 Months Ended
	Mar. 31, 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 March 31, 2019 As of December 31, 2018 (in thousands) Manufacturing-related deposits and prepaids $ 55,322 $ 39,036 Investment receivable 42,300 — Leasehold improvement receivable 13,474 13,474 Prepaid clinical and pre-clinical expenses 10,149 9,706 Prepaid maintenance services 3,538 2,994 Prepaid research expenses 3,091 1,932 Prepaid income tax 2,130 2,130 Interest receivable 1,285 1,918 Other 4,949 6,592 Total other current assets $ 136,238 $ 77,782 The following table summarizes the Company’s other non-current assets for each of the periods indicated: As of March 31, 2019 As of December 31, 2018 (in thousands) Manufacturing-related deposits $ 82,961 $ 62,821 Strategic investments 32,359 31,739 Restricted cash and investments 6,201 1,001 Prepaid clinical expenses 5,700 7,541 Alternative minimum tax credit 3,367 3,367 Other 2,725 825 Total other non-current assets $ 133,313 $ 107,294

ACCRUED EXPENSES

ACCRUED EXPENSES	3 Months Ended
	Mar. 31, 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 March 31, 2019 As of December 31, 2018 (in thousands) Product revenue related reserves $ 29,054 $ 26,146 Accrued contract manufacturing costs 16,369 15,794 Accrued employee compensation costs 14,763 24,692 Accrued clinical and pre-clinical costs 12,041 11,396 Accrued professional fees 8,000 11,319 Accrued BioMarin royalties 4,455 8,254 Accrued interest expense 3,183 1,045 Accrued property and equipment 2,878 5,421 Accrued collaboration cost sharing 2,458 2,167 Accrued research costs 1,815 1,070 Accrued milestone expense 1,517 24,020 Other 3,587 2,771 Total accrued expenses $ 100,120 $ 134,095

EQUITY FINANCING

EQUITY FINANCING	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
EQUITY FINANCING	10. EQUITY FINANCING In March 2019, the Company sold approximately 2.6 million shares of common stock through an underwritten public offering. The offering price was $140.41 per share. The Company received net proceeds of approximately $365.3 million from the offering, net of commission and offering expenses of approximately $0.4 million.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
STOCK-BASED COMPENSATION	11. STOCK-BASED COMPENSATION The following table summarizes the Company’s stock awards granted for each of the periods indicated: For the Three Months Ended March 31, 2019 2018 Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Stock options 990,234 $ 76.44 1,124,585 $ 34.08 Restricted stock units 324,630 $ 143.14 150,725 $ 71.45 Restricted stock awards — $ — 17,090 $ 71.45 Stock-based Compensation Expense For the three months ended March 31, 2019 and 2018, total stock-based compensation expense was $16.1 million and $10.5 million, respectively. The increase in stock-based compensation expense for the three months was driven by increases in headcount and stock price as well as the achievement of a milestone related to the March 2017 restricted stock units with performance conditions. For the Three Months Ended March 31, 2019 2018 (in thousands) Research and development $ 5,087 $ 2,060 Selling, general and administrative 11,052 8,466 Total stock-based compensation expense $ 16,139 $ 10,526 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 March 31, 2019 2018 (in thousands) Stock options $ 11,457 $ 8,973 Restricted stock awards/units 3,916 1,260 Employee stock purchase plan 766 293 Total stock-based compensation expense $ 16,139 $ 10,526

OTHER LOSS

OTHER LOSS	3 Months Ended
	Mar. 31, 2019
Other Income And Expenses [Abstract]
OTHER LOSS	12. OTHER LOSS The following table summarizes other loss for the periods indicated: For the Three Months Ended March 31, 2019 2018 (in thousand) Interest expense $ (7,335 ) $ (7,634 ) Interest income 2,361 1,872 Amortization of investment discount 4,332 1,259 Other income 470 18 Total other loss $ (172 ) $ (4,485 )

LEASES

LEASES	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
LEASES	13. 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, the Company entered into the seventh and eighth 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 163,842 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 right-of-use 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 de-recognized $18.0 million of deferred rent which served to reduce the right-of-use assets recognized on the balance sheet, in accordance with the transition guidance. As of March 31, 2019, operating lease assets were $41.1 million and operating lease liabilities were $58.9 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 months ended March 31, 2019: Operating Lease (in thousands) For the three months ended March 31, 2019 Lease cost Operating lease cost $ 2,602 Variable lease cost 1,129 Total lease cost $ 3,731 Other information Operating lease payments 2,376 Operating lease liabilities arising from obtaining right-of-use-assets — Weighted average remaining lease term 6.2 years Weighted average discount rate 7.50 % Future minimum lease payments under the Company’s non-cancelable operating leases as of March 31, 2019, are as follows: Maturity of lease liability (in thousands) As of March 31, 2019 2019 (April - December) $ 8,061 2020 11,395 2021 12,558 2022 10,737 2023 10,877 Thereafter 20,484 Total minimum lease payments 74,112 Less: imputed interest (15,183 ) Total operating lease liabilities $ 58,929 Included in the condensed consolidated balance sheet: Current portion of lease liabilities within other current liabilities $ 6,764 Lease liabilities 52,165 Total operating lease liabilities $ 58,929 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	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
NET LOSS PER SHARE	14. 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 months ended March 31, 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 March 31, 2019 2018 (in thousands, except per share amounts) Net loss $ (76,643 ) $ (35,363 ) Weighted-average number of shares of common stock and common stock equivalents outstanding: Weighted-average number of shares of common stock outstanding for computing basic loss earnings per share 71,731 64,631 Dilutive effect of outstanding stock awards and stock options after application of the treasury stock method* — — Weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for computing diluted loss per share 71,731 64,631 Net loss per share - basic and diluted $ (1.07 ) $ (0.55 ) * For the three months ended March 31, 2019 and 2018, stock options, RSAs, RSUs, stock appreciation rights to purchase 9.8 million and 9.9 million shares of the Company’s common stock, respectively, were excluded from the net loss per share calculation as their effect would have been anti-dilutive.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	15. COMMITMENTS AND CONTINGENCIES Manufacturing Obligations The Company has entered into long-term contractual arrangements from time to time for the provision of goods and services. 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 “Supply Agreement”) with Paragon. The 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 in a minimum amount of $4.0 million 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, including the Supply Agreement with Paragon: As of March 31, 2019 (in thousands) 2019 (April - December) $ 172,733 2020 124,052 2021 34,510 2022 42,204 2023 42,244 Thereafter 122,000 Total manufacturing commitments $ 537,743 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 March 31, 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)	3 Months Ended
	Mar. 31, 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 months ended March 31, 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 and cash, cash equivalents and investments held at financial institutions. As of March 31, 2019, the majority of the Company’s accounts receivable arose from product sales in the U.S. and all customers have standard payment terms which generally require payment within 30 to 61 days. Outside of the U.S., the payment terms range between 30 and 150 days. Three individual customers accounted for 41%, 40% and 15% of net product revenues for the three months ended March 31, 2019 and 57%, 26% and 8% of accounts receivable from product sales as of March 31, 2019. 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 March 31, 2019, the Company believes that such customers are of high credit quality. As of March 31, 2019 the Company’s cash equivalents and investments were concentrated at three financial institutions 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 institutions.
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 the cumulative impact 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 balances 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 March 31, 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 expense 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 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 classes of all underlying assets and will allocate the contract consideration to the lease component only. There have not been any other material changes to the Company’s accounting policies as of March 31, 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”. .

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Assets Measured and Carried at Fair Value	The tables below present information about the Company’s financial assets that are measured and carried at fair value and indicate the level within the fair value hierarchy of valuation techniques it utilizes to determine such fair value: Fair Value Measurement as of March 31, 2019 Total Level 1 Level 2 Level 3 (in thousands) Assets Money market funds $ 155,406 $ 155,406 $ — $ — Commercial paper 65,779 — 65,779 — Government and government agency bonds 807,025 807,025 — — Corporate bonds 33,582 33,582 — — Strategic equity investments 32,359 2,359 — 30,000 Certificates of deposit 1,001 1,001 — — Total $ 1,095,152 $ 999,373 $ 65,779 $ 30,000 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)	3 Months Ended
	Mar. 31, 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 March 31, 2019 As of December 31, 2018 (in thousands) Money market funds $ 155,406 $ 42,920 Government and government agency bonds 294,368 111,587 Commercial paper — 14,940 Total $ 449,774 $ 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 March 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value (in thousands) Cash and money market funds $ 437,822 $ — $ — $ 437,822 Commercial paper 65,779 — — $ 65,779 Government and government agency bonds 807,001 31 (7 ) $ 807,025 Corporate bonds 33,587 — (5 ) $ 33,582 Total cash, cash equivalents and investments $ 1,344,189 $ 31 $ (12 ) $ 1,344,208 As reported: Cash and cash equivalents $ 732,179 $ 11 $ — $ 732,190 Short-term investments 612,010 20 (12 ) $ 612,018 Total cash, cash equivalents and investments $ 1,344,189 $ 31 $ (12 ) $ 1,344,208 As of December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value (in thousands) Cash and money market funds $ 244,302 $ — $ — $ 244,302 Commercial paper 125,907 — — 125,907 Government and government agency bonds 760,258 12 (35 ) 760,235 Corporate bonds 43,544 — (76 ) 43,468 Total cash, cash equivalents and investments $ 1,174,011 $ 12 $ (111 ) $ 1,173,912 As reported: Cash and cash equivalents $ 370,827 $ 3 $ (1 ) $ 370,829 Short-term investments 803,184 9 (110 ) 803,083 Total cash, cash equivalents and investments $ 1,174,011 $ 12 $ (111 ) $ 1,173,912

ACCOUNTS RECEIVABLE AND RESER_2

ACCOUNTS RECEIVABLE AND RESERVES FOR PRODUCT SALES (Tables)	3 Months Ended
	Mar. 31, 2019
Receivables Net Current [Abstract]
Summary of Components of Accounts Receivable	The following table summarizes the components of the Company’s accounts receivable for the periods indicated: As of March 31, 2019 As of December 31, 2018 (in thousands) Product sales, net of discounts and allowances $ 49,718 $ 48,252 Government contract receivables 792 792 Total accounts receivable, net $ 50,510 $ 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 2,566 9,429 936 1,064 13,995 Payments/credits (3,049 ) (5,191 ) (791 ) (2,015 ) (11,046 ) Balance, as of March 31, 2019 $ 895 $ 28,514 $ 683 $ 1,367 $ 31,459
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 March 31, 2019 As of December 31, 2018 (in thousands) Reduction to accounts receivable $ 2,405 $ 2,364 Component of accrued expenses 29,054 26,146 Total reserves $ 31,459 $ 28,510

INVENTORY (Tables)

INVENTORY (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2019 As of December 31, 2018 (in thousands) Raw materials $ 70,271 $ 71,313 Work in progress 66,884 47,279 Finished goods 3,312 6,853 Total inventory $ 140,467 $ 125,445

OTHER CURRENT ASSETS AND OTHE_2

OTHER CURRENT ASSETS AND OTHER NON-CURRENT ASSETS (Tables)	3 Months Ended
	Mar. 31, 2019
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Summary of Other Current Assets	The following table summarizes the Company’s other current assets for each of the periods indicated: As of March 31, 2019 As of December 31, 2018 (in thousands) Manufacturing-related deposits and prepaids $ 55,322 $ 39,036 Investment receivable 42,300 — Leasehold improvement receivable 13,474 13,474 Prepaid clinical and pre-clinical expenses 10,149 9,706 Prepaid maintenance services 3,538 2,994 Prepaid research expenses 3,091 1,932 Prepaid income tax 2,130 2,130 Interest receivable 1,285 1,918 Other 4,949 6,592 Total other current assets $ 136,238 $ 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 March 31, 2019 As of December 31, 2018 (in thousands) Manufacturing-related deposits $ 82,961 $ 62,821 Strategic investments 32,359 31,739 Restricted cash and investments 6,201 1,001 Prepaid clinical expenses 5,700 7,541 Alternative minimum tax credit 3,367 3,367 Other 2,725 825 Total other non-current assets $ 133,313 $ 107,294

ACCRUED EXPENSES (Tables)

ACCRUED EXPENSES (Tables)	3 Months Ended
	Mar. 31, 2019
Payables And Accruals [Abstract]
Summary of Accrued Expenses	The following table summarizes the Company’s accrued expenses for each of the periods indicated: As of March 31, 2019 As of December 31, 2018 (in thousands) Product revenue related reserves $ 29,054 $ 26,146 Accrued contract manufacturing costs 16,369 15,794 Accrued employee compensation costs 14,763 24,692 Accrued clinical and pre-clinical costs 12,041 11,396 Accrued professional fees 8,000 11,319 Accrued BioMarin royalties 4,455 8,254 Accrued interest expense 3,183 1,045 Accrued property and equipment 2,878 5,421 Accrued collaboration cost sharing 2,458 2,167 Accrued research costs 1,815 1,070 Accrued milestone expense 1,517 24,020 Other 3,587 2,771 Total accrued expenses $ 100,120 $ 134,095

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	3 Months Ended
	Mar. 31, 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 March 31, 2019 2018 Grants Weighted Average Grant Date Fair Value Grants Weighted Average Grant Date Fair Value Stock options 990,234 $ 76.44 1,124,585 $ 34.08 Restricted stock units 324,630 $ 143.14 150,725 $ 71.45 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 March 31, 2019 2018 (in thousands) Research and development $ 5,087 $ 2,060 Selling, general and administrative 11,052 8,466 Total stock-based compensation expense $ 16,139 $ 10,526
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 March 31, 2019 2018 (in thousands) Stock options $ 11,457 $ 8,973 Restricted stock awards/units 3,916 1,260 Employee stock purchase plan 766 293 Total stock-based compensation expense $ 16,139 $ 10,526

OTHER LOSS (Tables)

OTHER LOSS (Tables)	3 Months Ended
	Mar. 31, 2019
Other Income And Expenses [Abstract]
Summary of Other Loss	The following table summarizes other loss for the periods indicated: For the Three Months Ended March 31, 2019 2018 (in thousand) Interest expense $ (7,335 ) $ (7,634 ) Interest income 2,361 1,872 Amortization of investment discount 4,332 1,259 Other income 470 18 Total other loss $ (172 ) $ (4,485 )

LEASES (Tables)

LEASES (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Summary of Lease Costs Recognized Under Topic 842 and Other Information Pertaining to Operating Leases	The following table contains a summary of the lease costs recognized under Topic 842 and other information pertaining to the Company’s operating leases for the three months ended March 31, 2019: Operating Lease (in thousands) For the three months ended March 31, 2019 Lease cost Operating lease cost $ 2,602 Variable lease cost 1,129 Total lease cost $ 3,731 Other information Operating lease payments 2,376 Operating lease liabilities arising from obtaining right-of-use-assets — Weighted average remaining lease term 6.2 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 March 31, 2019, are as follows: Maturity of lease liability (in thousands) As of March 31, 2019 2019 (April - December) $ 8,061 2020 11,395 2021 12,558 2022 10,737 2023 10,877 Thereafter 20,484 Total minimum lease payments 74,112 Less: imputed interest (15,183 ) Total operating lease liabilities $ 58,929 Included in the condensed consolidated balance sheet: Current portion of lease liabilities within other current liabilities $ 6,764 Lease liabilities 52,165 Total operating lease liabilities $ 58,929
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)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Basic and Diluted Net Loss Per Share	For the three months ended March 31, 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 March 31, 2019 2018 (in thousands, except per share amounts) Net loss $ (76,643 ) $ (35,363 ) Weighted-average number of shares of common stock and common stock equivalents outstanding: Weighted-average number of shares of common stock outstanding for computing basic loss earnings per share 71,731 64,631 Dilutive effect of outstanding stock awards and stock options after application of the treasury stock method* — — Weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for computing diluted loss per share 71,731 64,631 Net loss per share - basic and diluted $ (1.07 ) $ (0.55 ) * For the three months ended March 31, 2019 and 2018, stock options, RSAs, RSUs, stock appreciation rights to purchase 9.8 million and 9.9 million shares of the Company’s common stock, respectively, were excluded from the net loss per share calculation as their effect would have been anti-dilutive.

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	3 Months Ended
	Mar. 31, 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, including the Supply Agreement with Paragon: As of March 31, 2019 (in thousands) 2019 (April - December) $ 172,733 2020 124,052 2021 34,510 2022 42,204 2023 42,244 Thereafter 122,000 Total manufacturing commitments $ 537,743

Organization and Nature of Bu_2

Organization and Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Cash, cash equivalents and investments	$ 1,350,400
Cash and cash equivalents	732,190	$ 370,829	$ 557,234
Short-term investments	612,018	803,083
Restricted cash and investments	$ 6,201	$ 1,001

Summary of Significant Accoun_3

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)Segment	Jan. 01, 2019USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment	1
Right-of-use assets	$ 41,098
Operating lease liabilities	58,929
ASU No. 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Right-of-use assets	42,500	$ 42,500
Operating lease liabilities	$ 60,100	$ 60,100
Product Revenues [Member] | Customer One [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	41.00%
Product Revenues [Member] | Customer Two [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	40.00%
Product Revenues [Member] | Customer Three [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	15.00%
Accounts Receivable [Member] | Customer One [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	57.00%
Accounts Receivable [Member] | Customer Two [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	26.00%
Accounts Receivable [Member] | Customer Three [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration of credit risk percentage	8.00%
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_2

License and Collaboration Agreements - Additional Information (Detail) - USD ($)	Apr. 04, 2019	Feb. 27, 2019	May 03, 2018	Jun. 30, 2019	Mar. 31, 2019	Mar. 31, 2018
Myonexus Therapeutics, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Final exercise price		$ 165,000,000
Additional transaction fees		8,700,000
Additional development milestone payments to be paid		$ 200,000,000
Myonexus Therapeutics, Inc. [Member] | Scenario Forecast [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
In-process research and development expense				$ 168,700,000
Myonexus Therapeutics, Inc. [Member] | Subsequent Event [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Date of acquisition	Apr. 4, 2019
Warrant Agreement [Member] | Myonexus Therapeutics, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Up-front cash payment under agreements			$ 60,000,000
Cash consideration under agreement excluding contingent payments			$ 200,000,000
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					$ 1,100,000	$ 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					$ 555,800,000

Assets Measured and Carried at

Assets Measured and Carried at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 1,095,152	$ 1,005,270
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	155,406	42,920
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	65,779	125,907
Government and Government Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	807,025	760,235
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	33,582	43,468
Strategic Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	32,359	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	999,373	849,363
Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	155,406	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	807,025	760,235
Level 1 [Member] | Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	33,582	43,468
Level 1 [Member] | Strategic Equity Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	2,359	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	65,779	125,907
Level 2 [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	65,779	125,907
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	30,000	30,000
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	Mar. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash equivalents	$ 449,774	$ 169,447
Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash equivalents	155,406	42,920
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Cash equivalents	$ 294,368	111,587
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Cash equivalents		$ 14,940

Cash, Cash Equivalents and Ma_3

Cash, Cash Equivalents and Marketable Securities - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Cash And Cash Equivalents [Abstract]
Weighted average maturity period of available-for-sale securities	2 months	2 months

Summary of Company Cash, Cash E

Summary of Company Cash, Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	$ 732,179	$ 370,827
Cash and cash equivalents, Gross unrealized gains	11	3
Cash and cash equivalents, Gross unrealized losses		(1)
Cash and cash equivalents	732,190	370,829	$ 557,234
Cash, cash equivalents and investments, Amortized cost	1,344,189	1,174,011
Cash, cash equivalents and investments, Gross unrealized gains	31	12
Cash, cash equivalents and investments, Gross unrealized losses	(12)	(111)
Cash, cash equivalents and investments, Fair market value	1,344,208	1,173,912
Available for sale debt securities current, Amortized cost	612,010	803,184
Available for sale debt securities current, Gross unrealized gains	20	9
Available for sale debt securities current, Gross unrealized losses	(12)	(110)
Available for sale debt securities current, Fair market value	612,018	803,083
Cash and Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, Amortized cost	437,822	244,302
Cash and cash equivalents	437,822	244,302
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost	65,779	125,907
Available for sale debt securities, Fair market value	65,779	125,907
Government and Government Agency Bonds [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost	807,001	760,258
Available for sale debt securities, Gross unrealized gains	31	12
Available for sale debt securities, Gross unrealized losses	(7)	(35)
Available for sale debt securities, Fair market value	807,025	760,235
Corporate Bonds [Member]
Cash and Cash Equivalents [Line Items]
Available for sale debt securities, Amortized cost	33,587	43,544
Available for sale debt securities, Gross unrealized losses	(5)	(76)
Available for sale debt securities, Fair market value	$ 33,582	$ 43,468

Summary of Components of Accoun

Summary of Components of Accounts Receivable (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Receivables Net Current [Abstract]
Product sales, net of discounts and allowances	$ 49,718	$ 48,252
Government contract receivables	792	792
Total accounts receivable, net	$ 50,510	$ 49,044

Summary of Change in Reserves f

Summary of Change in Reserves for Discounts and Allowances (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	$ 28,510
Provision	13,995
Payments/credits	(11,046)
Balance, as of March 31, 2019	31,459
Chargebacks [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	1,378
Provision	2,566
Payments/credits	(3,049)
Balance, as of March 31, 2019	895
Rebates [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	24,276
Provision	9,429
Payments/credits	(5,191)
Balance, as of March 31, 2019	28,514
Prompt Pay [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	538
Provision	936
Payments/credits	(791)
Balance, as of March 31, 2019	683
Other Accruals [Member]
Accounts Notes And Loans Receivable [Line Items]
Balance, as of December 31, 2018	2,318
Provision	1,064
Payments/credits	(2,015)
Balance, as of March 31, 2019	$ 1,367

Summary of Total Reserves Inclu

Summary of Total Reserves Included in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Receivables Net Current [Abstract]
Reduction to accounts receivable	$ 2,405	$ 2,364
Component of accrued expenses	29,054	26,146
Total reserves	$ 31,459	$ 28,510

Summary of Components of Invent

Summary of Components of Inventory (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 70,271	$ 71,313
Work in progress	66,884	47,279
Finished goods	3,312	6,853
Total inventory	$ 140,467	$ 125,445

Summary of Other Current Assets

Summary of Other Current Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Prepaid Expense And Other Assets Current [Abstract]
Manufacturing-related deposits and prepaids	$ 55,322	$ 39,036
Investment receivable	42,300
Leasehold improvement receivable	13,474	13,474
Prepaid clinical and pre-clinical expenses	10,149	9,706
Prepaid maintenance services	3,538	2,994
Prepaid research expenses	3,091	1,932
Prepaid income tax	2,130	2,130
Interest receivable	1,285	1,918
Other	4,949	6,592
Total other current assets	$ 136,238	$ 77,782

Summary of Other Non-current As

Summary of Other Non-current Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Prepaid Expense And Other Assets Noncurrent [Abstract]
Manufacturing-related deposits	$ 82,961	$ 62,821
Strategic investments	32,359	31,739
Restricted cash and investments	6,201	1,001
Prepaid clinical expenses	5,700	7,541
Alternative minimum tax credit	3,367	3,367
Other	2,725	825
Total other non-current assets	$ 133,313	$ 107,294

Summary of Accrued Expenses (De

Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Product revenue related reserves	$ 29,054	$ 26,146
Accrued contract manufacturing costs	16,369	15,794
Accrued employee compensation costs	14,763	24,692
Accrued clinical and pre-clinical costs	12,041	11,396
Accrued professional fees	8,000	11,319
Accrued BioMarin royalties	4,455	8,254
Accrued interest expense	3,183	1,045
Accrued property and equipment	2,878	5,421
Accrued collaboration cost sharing	2,458	2,167
Accrued research costs	1,815	1,070
Accrued milestone expense	1,517	24,020
Other	3,587	2,771
Total accrued expenses	$ 100,120	$ 134,095

Equity Financing - Additional I

Equity Financing - Additional Information (Detail) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended
	Mar. 31, 2019USD ($)$ / sharesshares
Class Of Stock [Line Items]
Common stock average price per share | $ / shares	$ 140.41
Net proceeds from issue of common stock	$ 365.3
Underwriting discounts, commission and offering expenses	$ 0.4
Underwritten Public Offering [Member]
Class Of Stock [Line Items]
Common stock issued | shares	2.6

Summary of Stock Awards Granted

Summary of Stock Awards Granted (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants, Stock options	990,234	1,124,585
Weighted Average Grant Date Fair Value, Stock options	$ 76.44	$ 34.08
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants, Restricted stock units and awards	324,630	150,725
Weighted Average Grant Date Fair Value, Restricted stock units and awards	$ 143.14	$ 71.45
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
	Mar. 31, 2019	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Share-based compensation expense	$ 16,139	$ 10,526

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
	Mar. 31, 2019	Mar. 31, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 16,139	$ 10,526
Research and Development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	5,087	2,060
Selling, General and Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 11,052	$ 8,466

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
	Mar. 31, 2019	Mar. 31, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 16,139	$ 10,526
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	11,457	8,973
Restricted Stock Awards/Units (RSAs/RSUs) [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	3,916	1,260
Employee Stock Purchase Plan [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 766	$ 293

Summary of Other Loss (Detail)

Summary of Other Loss (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Nonoperating Income Expense [Abstract]
Interest expense	$ (7,335)	$ (7,634)
Interest income	2,361	1,872
Amortization of investment discount	4,332	1,259
Other income	470	18
Other loss	$ (172)	$ (4,485)

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)ft²	Jan. 01, 2019USD ($)
Lessee Lease Description [Line Items]
Operating lease liabilities | $	$ 58,929
Right-of-use assets | $	41,098
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	163,842

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
	Mar. 31, 2019USD ($)
Lease cost
Operating lease cost	$ 2,602
Variable lease cost	1,129
Total lease cost	3,731
Other information
Operating lease payments	$ 2,376
Weighted average remaining lease term	6 years 2 months 12 days
Weighted average discount rate	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	Mar. 31, 2019USD ($)
Maturity of lease liability
2019 (April - December)	$ 8,061
2020	11,395
2021	12,558
2022	10,737
2023	10,877
Thereafter	20,484
Total minimum lease payments	74,112
Less: imputed interest	(15,183)
Total operating lease liabilities	58,929
Included in the condensed consolidated balance sheet:
Current portion of lease liabilities within other current liabilities	$ 6,764
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent
Lease liabilities	$ 52,165
Total operating lease liabilities	$ 58,929

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
		Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net loss		$ (76,643)	$ (35,363)
Weighted-average number of shares of common stock and common stock equivalents outstanding:
Weighted-average number of shares of common stock outstanding for computing basic loss earnings per share		71,731	64,631
Dilutive effect of outstanding stock awards and stock options after application of the treasury stock method	[1]	0	0
Weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for computing diluted loss per share		71,731	64,631
Net loss per share - basic and diluted		$ (1.07)	$ (0.55)
[1]	For the three months ended March 31, 2019 and 2018, stock options, RSAs, RSUs, stock appreciation rights to purchase 9.8 million and 9.9 million shares of the Company’s common stock, respectively, were excluded from the 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
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Anti-dilutive securities excluded from computation of net loss per share	9.8	9.9

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - Paragon [Member] $ in Millions	Feb. 22, 2019USD ($)	Oct. 31, 2018Suite
Manufacturing Collaboration Agreement [Member]
Commitments And Contingencies [Line Items]
Number of dedicated clean room suites		2
Number of additional clean room suites available on optional reserve		2
Agreement expiration date		Dec. 31, 2024
Manufacturing Supply Agreement [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	Mar. 31, 2019USD ($)
Commitments And Contingencies [Line Items]
2019 (April - December)	$ 172,733
2020	124,052
2021	34,510
2022	42,204
2023	42,244
Thereafter	122,000
Total manufacturing commitments	$ 537,743