Sage Therapeutics (SAGE) 10-Q 6 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Jul. 31, 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	SAGE
Entity Registrant Name	Sage Therapeutics, Inc.
Entity Central Index Key	0001597553
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		51,656,993
Entity Shell Company	false
Entity File Number	001-36544
Entity Tax Identification Number	274486580
Entity Address, Address Line One	215 First Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	Massachusetts
Entity Address, Postal Zip Code	02142
City Area Code	(617)
Local Phone Number	299-8380

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 166,185	$ 190,943
Marketable securities	1,070,364	731,833
Prepaid expenses and other current assets	27,021	21,919
Total current assets	1,263,570	944,695
Property and equipment, net	8,363	5,643
Restricted cash	2,367	2,367
Right of use operating asset	37,224
Other long-term assets	4,023
Total assets	1,315,547	952,705
Current liabilities:
Accounts payable	12,431	34,036
Accrued expenses	58,912	51,994
Other current liabilities	7,610
Total current liabilities	78,953	86,030
Long-term lease operating liability, net of current portion	33,309
Other long-term liabilities	410	3,704
Total liabilities	112,672	89,734
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at June 30, 2019 and December 31, 2018; no shares issued or outstanding at June 30, 2019 and December 31, 2018
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at June 30, 2019 and December 31, 2018; 51,472,137 and 46,891,296 shares issued at June 30, 2019 and December 31, 2018; 51,469,104 and 46,888,263 shares outstanding at June 30, 2019 and December 31, 2018	5	5
Treasury stock, at cost, 3,033 shares at June 30, 2019 and December 31, 2018	(400)	(211)
Additional paid-in capital	2,496,651	1,827,021
Accumulated deficit	(1,294,956)	(963,329)
Accumulated other comprehensive gain (loss)	1,575	(515)
Total stockholders’ equity	1,202,875	862,971
Total liabilities and stockholders’ equity	$ 1,315,547	$ 952,705

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	51,472,137	46,891,296
Common stock, shares outstanding	51,469,104	46,888,263
Treasury stock, shares	3,033	3,033

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Total revenue	$ 873	$ 90,000	$ 1,338	$ 90,000
Operating costs and expenses:
Cost of goods sold	44		44
Research and development	89,059	68,980	175,457	118,250
Selling, general and administrative	88,227	43,167	172,146	72,016
Total operating costs and expenses	177,330	112,147	347,647	190,266
Loss from operations	(176,457)	(22,147)	(346,309)	(100,266)
Interest income, net	8,220	5,137	14,662	8,666
Other income, net	16	32	20	24
Net loss	$ (168,221)	$ (16,978)	$ (331,627)	$ (91,576)
Net loss per share—basic and diluted	$ (3.28)	$ (0.36)	$ (6.65)	$ (2.02)
Weighted average number of common shares outstanding—basic and diluted	51,257,640	46,541,716	49,882,377	45,439,666
Comprehensive loss:
Net loss	$ (168,221)	$ (16,978)	$ (331,627)	$ (91,576)
Other comprehensive items:
Unrealized gain (loss) on marketable securities	1,681	40	2,090	(116)
Total other comprehensive gain (loss)	1,681	40	2,090	(116)
Total comprehensive loss	(166,540)	(16,938)	(329,537)	(91,692)
Product Revenue [Member]
Total revenue	519		519
Collaboration Revenue [Member]
Total revenue	$ 354	$ 90,000	$ 819	$ 90,000

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Net loss	$ (331,627)	$ (91,576)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	78,883	44,845
Premium on marketable securities	(1,887)	(75)
Amortization of discount on marketable securities	(4,973)	(4,154)
Depreciation	920	493
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(5,102)	(25,091)
Other long-term assets	(4,023)
Right of use operating asset	4,713
Operating lease liabilities	(4,346)
Accounts payable	(21,806)	(903)
Accrued expenses and other liabilities	5,970	(2,245)
Net cash used in operating activities	(283,278)	(78,706)
Cash flows from investing activities
Proceeds from sales and maturities of marketable securities	588,652	263,460
Purchases of marketable securities	(918,233)	(813,337)
Purchases of property and equipment	(3,438)	(1,054)
Net cash used in investing activities	(333,019)	(550,931)
Cash flows from financing activities
Proceeds from stock option exercises and employee stock purchase plan issuances	31,282	19,402
Payment of employee tax obligations related to vesting of restricted stock units	(692)	(904)
Payments of offering costs	(328)	(340)
Proceeds from public offerings of common stock, net of commissions and underwriting discounts	561,277	631,494
Net cash provided by financing activities	591,539	649,652
Net increase (decrease) in cash, cash equivalents and restricted cash	(24,758)	20,015
Cash, cash equivalents and restricted cash at beginning of period	193,310	307,084
Cash, cash equivalents and restricted cash at end of period	168,552	327,099
Supplemental disclosure of non-cash operating and investing activities
Purchases of property and equipment included in accounts payable	252	$ 10
Right of use assets obtained in exchange for new operating lease liabilities	$ 872

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Balances at Dec. 31, 2017	$ 475,475	$ 5	$ (113)	$ 1,066,059	$ (29)	$ (590,447)
Balances, Shares at Dec. 31, 2017		42,002,934	960
Issuance of common stock from exercise of stock options, Amount	11,727			11,727
Issuance of common stock from exercise of stock options, Shares		402,227
Issuance of common stock under employee stock purchase plan	1,127			1,127
Issuance of common stock under employee stock purchase plan, Shares		11,683
Purchase of treasury stock, Amount	(98)		$ (98)
Purchase of treasury stock, Shares			554
Stock-based compensation expense	15,549			15,549
Public offering of common stock, net of offering costs, Amount	631,154			631,154
Public offering of common stock, net of offering costs, Shares		4,032,012
Unrealized loss on available-for-sale securities	(156)				(156)
Vesting of restricted stock units, net of employee tax obligations	(904)			(904)
Vesting of restricted stock units, net of employee tax obligations, Shares		9,442
Net loss	(74,598)					(74,598)
Balances at Mar. 31, 2018	1,059,276	$ 5	$ (211)	1,724,712	(185)	(665,045)
Balances, Shares at Mar. 31, 2018		46,458,298	1,514
Balances at Dec. 31, 2017	475,475	$ 5	$ (113)	1,066,059	(29)	(590,447)
Balances, Shares at Dec. 31, 2017		42,002,934	960
Net loss	(91,576)
Balances at Jun. 30, 2018	1,077,763	$ 5	$ (211)	1,760,137	(145)	(682,023)
Balances, Shares at Jun. 30, 2018		46,603,839	1,514
Balances at Mar. 31, 2018	1,059,276	$ 5	$ (211)	1,724,712	(185)	(665,045)
Balances, Shares at Mar. 31, 2018		46,458,298	1,514
Issuance of common stock from exercise of stock options, Amount	6,643			6,643
Issuance of common stock from exercise of stock options, Shares		145,541
Stock-based compensation expense	28,782			28,782
Unrealized loss on available-for-sale securities	40				40
Net loss	(16,978)					(16,978)
Balances at Jun. 30, 2018	1,077,763	$ 5	$ (211)	1,760,137	(145)	(682,023)
Balances, Shares at Jun. 30, 2018		46,603,839	1,514
Balances at Dec. 31, 2018	862,971	$ 5	$ (211)	1,827,021	(515)	(963,329)
Balances, Shares at Dec. 31, 2018		46,888,263	3,033
Issuance of common stock from exercise of stock options, Amount	14,072			14,072
Issuance of common stock from exercise of stock options, Shares		287,659
Issuance of common stock under employee stock purchase plan	1,799			1,799
Issuance of common stock under employee stock purchase plan, Shares		16,398
Purchase of treasury stock, Amount	(189)		$ (189)
Stock-based compensation expense	43,622			43,622
Public offering of common stock, net of offering costs, Amount	560,948			560,948
Public offering of common stock, net of offering costs, Shares		3,833,334
Unrealized loss on available-for-sale securities	409				409
Vesting of restricted stock units, net of employee tax obligations	(692)			(692)
Vesting of restricted stock units, net of employee tax obligations, Shares		8,518
Net loss	(163,406)					(163,406)
Balances at Mar. 31, 2019	1,319,534	$ 5	$ (400)	2,446,770	(106)	(1,126,735)
Balances, Shares at Mar. 31, 2019		51,034,172	3,033
Balances at Dec. 31, 2018	862,971	$ 5	$ (211)	1,827,021	(515)	(963,329)
Balances, Shares at Dec. 31, 2018		46,888,263	3,033
Net loss	(331,627)
Balances at Jun. 30, 2019	1,202,875	$ 5	$ (400)	2,496,651	1,575	(1,294,956)
Balances, Shares at Jun. 30, 2019		51,469,104	3,033
Balances at Mar. 31, 2019	1,319,534	$ 5	$ (400)	2,446,770	(106)	(1,126,735)
Balances, Shares at Mar. 31, 2019		51,034,172	3,033
Issuance of common stock from exercise of stock options, Amount	15,601			15,601
Issuance of common stock from exercise of stock options, Shares		434,932
Stock-based compensation expense	34,280			34,280
Unrealized loss on available-for-sale securities	1,681				1,681
Net loss	(168,221)					(168,221)
Balances at Jun. 30, 2019	$ 1,202,875	$ 5	$ (400)	$ 2,496,651	$ 1,575	$ (1,294,956)
Balances, Shares at Jun. 30, 2019		51,469,104	3,033

Nature of the Business

Nature of the Business	6 Months Ended
	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Sage Therapeutics, Inc. (“Sage” or the “Company”) is a biopharmaceutical company committed to developing and commercializing novel medicines with the potential to transform the lives of people with debilitating disorders of the brain. The Company’s lead product, ZULRESSO™ (brexanolone) injection, was approved by the U.S. Food and Drug Administration (“FDA”) in March 2019, for the treatment of postpartum depression (“PPD”) in adults, and was made commercially available in the U.S. beginning on June 24, 2019 after completion of controlled substance scheduling of brexanolone by the U.S. Drug Enforcement Administration and incorporation of the scheduling into the FDA-approved label and other product information. The Company has a portfolio of other product candidates with a current focus on modulating two critical CNS receptor systems, GABA and NMDA. The GABA receptor family, which is recognized as the major inhibitory neurotransmitter in the CNS, mediates downstream neurologic and bodily function via activation of GABA A The Company was incorporated under the laws of the State of Delaware on April 16, 2010, and commenced operations on January 19, 2011 as Sterogen Biopharma, Inc. On September 13, 2011, the Company changed its name to Sage Therapeutics, Inc. The Company is subject to risks and uncertainties common to companies in the biotech and pharmaceutical industries, including, but not limited to, the risks associated with developing product candidates at each stage of non-clinical and clinical development; the challenges associated with gaining regulatory approval of such product candidates; the risks associated with commercializing pharmaceutical products for marketing and sale; the potential for development by third parties of new technological innovations that may compete with the Company’s products; the dependence on key personnel; the challenges of protecting proprietary technology; the need to comply with government regulations; the high costs of drug development; and the uncertainty of being able to secure additional capital when needed to fund operations. Under Accounting Standards Update (“ASU”) 2014-15, Presentation of Financial Statements—Going Concern Until such time, if ever, as the Company can generate substantial product revenue and achieve profitability, the Company expects to finance its cash needs through a combination of equity offerings, debt financings, collaborations, strategic alliances, licensing arrangements and other sources of funding. If the Company is unable to raise additional funds through equity or debt financings when needed, the Company may be required to delay, limit, reduce or terminate product development or future commercialization efforts or grant rights to develop and market products or product candidates that the Company would otherwise prefer to develop and market itself.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies The following is a summary of significant accounting policies followed in the preparation of these unaudited condensed consolidated financial statements. Basis of Presentation The unaudited interim condensed consolidated financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2018, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements. In the opinion of the Company’s management, the accompanying unaudited condensed consolidated financial statements contain all adjustments, consisting of only normal recurring adjustments, necessary for a fair statement of its financial position as of June 30, 2019, its results of operations and comprehensive loss for the three and six months ended June 30, 2019 and 2018, its cash flows for the six months ended June 30, 2019 and 2018, and its statements of changes in stockholders’ equity for the six months ended June 30, 2019 and 2018. The consolidated balance sheet at December 31, 2018 was derived from audited financial statements, but does not include all disclosures required by GAAP. The results for the three and six months ended June 30, 2019 are not necessarily indicative of the results for the year ending December 31, 2019, or for any future period. Principles of Consolidation The unaudited interim condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries as disclosed in Note 2, Summary of Significant Accounting Policies, within the “Notes to Consolidated Financial Statements” accompanying its Annual Report on Form 10-K for the fiscal year ended December 31, 2018. Intercompany accounts and transactions have been eliminated. Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Research and Development Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries and benefits, overhead costs, depreciation, contract services and other related costs. Research and development costs are expensed to operations as the related obligation is incurred. The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the U.S. These agreements are generally cancelable, and related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by the Company. The historical accrual estimates made by the Company have not been materially different from the actual costs. Stock-Based Compensation The Company recognizes compensation expense for stock-based awards, including grants of stock options and restricted stock, made to employees and non-employee directors based on the estimated fair value on the date of grant, over the requisite service period. Effective January 1, 2019, the Company recognizes compensation expense for stock-based awards, including grants of stock options and restricted stock, made to non-employee consultants based on the estimated fair value on the date of grant, over the requisite service period. Through December 31, 2018, the Company recognized compensation expense for stock-based awards granted to non-employee consultants based on the fair value of the awards on each date on which the awards vest. Compensation expense was recognized over the vesting period, provided that services were rendered by such non-employee consultants during that time. At the end of each financial reporting period, the fair value of unvested options was re-measured using the then-current fair value of the common stock of the Company and updated assumptions in the Black-Scholes option-pricing model. For awards that vest upon achievement of a performance condition, the Company recognizes compensation expense when achievement of the performance condition is met or during the period from which meeting the condition is deemed probable until the expected date of meeting the performance condition. The fair value of each option grant is estimated using the Black-Scholes option-pricing model. Through December 31, 2015, the Company lacked sufficient Company-specific historical and implied volatility information, and as a result, the Company used the volatility of a group of publicly-traded peer companies in the Black-Scholes calculations. Beginning in 2016, the Company estimated its expected volatility using a weighted average of the historical volatility of publicly-traded peer companies and the volatility of its common stock and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its traded stock price for the duration of the expected term. The expected term of the options granted to employees and non-employee directors by the Company has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. Through December 31, 2018, the expected term of its options granted to non-employee consultants has been determined based on the contractual term of the options, and effective January 1, 2019, the “simplified” method is used. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. The expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The Company also applies a forfeiture rate in order to calculate stock-based compensation expense. Expected forfeitures are based on the historical experience of the Company and management’s expectations of future forfeitures. To the extent actual forfeitures differ from the estimates, the difference is recorded as a cumulative adjustment in the period in which the estimates are revised. The Company recognizes stock-based compensation expense for only the portion of awards that are expected to vest. Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of 90 days or less at the date of purchase to be cash equivalents. As of June 30, 2019 and December 31, 2018, cash equivalents were comprised of cash equivalents and money market funds. Marketable securities Marketable securities consist of investments with original maturities greater than 90 days. The Company has classified its investments with maturities beyond one year as short-term, based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. The Company considers its investment portfolio of investments to be available-for-sale. Accordingly, these investments are recorded at fair value, which is based on quoted market prices. Unrealized gains and losses are reported as a component of accumulated other comprehensive items in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other expense, net, based on the specific identification method. When determining whether a decline in value is other than temporary, the Company considers several factors, including whether the Company has the intent to sell the security, and whether it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis. No declines in value were deemed to be other than temporary during the three and six months ended June 30, 2019 and 2018. Fair Value Measurements Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Financial assets and liabilities carried at fair value are classified and disclosed in one of the following three categories: Level 1 — Quoted market prices in active markets for identical assets or liabilities. Level 2 — Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The Company’s cash equivalents and marketable securities at June 30, 2019 and December 31, 2018 were carried at fair value, determined according to the fair value hierarchy; see Footnote 3, Fair Value Measurements herein. The carrying amounts reflected in the unaudited condensed consolidated balance sheets for accounts payable and accrued expenses approximate their fair values due to their short-term maturities at June 30, 2019 and December 31, 2018, respectively. Revenue Recognition Effective January 1, 2017, the Company adopted Accounting Standards Codification (“ASC”), Topic 606, Revenue from Contracts with Customers The Company received approval of ZULRESSO from the FDA in March 2019 and subsequently began to record revenues from product sales in June 2019. Prior to the second quarter of 2019, all of the revenues of the Company were derived from the Company’s collaboration agreement with Shionogi & Co., Ltd., (“Shionogi”). The terms of the Company’s collaboration agreement include consideration such as non-refundable license fees, funding of research and development services, payments due upon the achievement of clinical and pre-clinical performance-based development milestones, regulatory milestones, manufacturing services to supply drug product for clinical trials, and sales-based milestones and royalties on product sales. Under Topic 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price, including variable consideration, if any; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. For contracts determined to be within the scope of Topic 606, the Company assesses whether the goods or services promised within each contract are distinct to identify those that are performance obligations. This assessment involves subjective determinations and requires management to make judgments about the individual promised goods or services and whether such are separable from the other aspects of the contractual relationship. Promised goods and services are considered distinct provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. The Company allocates the transaction price (the amount of consideration it expects to be entitled to from a customer in exchange for the promised goods or services) to each performance obligation and recognizes the associated revenue when (or as) each performance obligation is satisfied. The Company’s estimate of the transaction price for each contract includes all variable consideration to which the Company expects to be entitled. Collaboration and license revenue In assessing whether a promised good or service is distinct in the evaluation of a collaboration or license arrangement subject to Topic 606, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. The Company also considers the intended benefit of the contract in assessing whether a promised good or service is separately identifiable from other promises in the contract. If a promised good or service is not distinct, the Company is required to combine that good or service with other promised goods or services until it identifies a bundle of goods or services that is distinct. The transaction price is then determined and allocated to the identified performance obligations in proportion to their standalone selling prices (“SSP”) on a relative SSP basis. SSP is determined at contract inception and is not updated to reflect changes between contract inception and when the performance obligations are satisfied. Determining the SSP for performance obligations requires significant judgment. In developing the SSP for a performance obligation, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. In certain circumstances, the Company may apply the residual method to determine the SSP of a good or service if the standalone selling price is considered highly variable or uncertain. The Company validates the SSP for performance obligations by evaluating whether changes in the key assumptions used to determine the SSP will have a significant effect on the allocation of arrangement consideration between multiple performance obligations. If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company assessed its arrangement with Shionogi and concluded that a significant financing component does not exist. For arrangements with licenses of intellectual property that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes royalty revenue and sales-based milestones at the later of (i) when the related sales occur, or (ii) when the performance obligation to which the royalty has been allocated has been satisfied. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied at a point in time or over time, and if over time this is based on the use of an output or input method. To date, revenue from the Company’s collaboration agreement with Shionogi has come from an initial, up-front fee upon execution of the agreement and payment for the supply of SAGE-217 drug product for Shionogi clinical trials. Product revenue The Company recognizes product revenues, net of variable consideration related to certain allowances and accruals that are determined using the expected value method, in its consolidated financial statements at the point in time when delivery is made and when control transfers to the customer, which is typically when the product has been delivered to the customer’s location. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. The Company’s only performance obligation identified for ZULRESSO is to deliver the product to the location specified by the customer’s order. The Company records shipping and handling costs associated with delivery of product to its customers within selling, general and administrative expenses on its consolidated statements of operations and comprehensive loss. The Company expense s incremental costs of obtaining a contract as incurred if the expected amortization period of the asset would be less than one year. I f the C ompany were to incur incremental costs with an amortization period greater than a year, such costs would be capitalized as contract assets, as they are expected to be recovered , and would be expensed by amortizing on a systematic basis that is consistent with the transfer to the customer of the goods or services to which the asset relates . The Company did not have any contract assets (unbilled receivables) at June 30, 2019, as customer invoicing generally occurs before or at the time of revenue recognition. The Company did not have any contract liabilities at June 30, 2019, as the Company did not receive any payments in advance of satisfying its performance obligations to its customers. Amounts billed or invoiced are included in prepaid expenses and other current assets on the consolidated balance sheets. The Company records reserves, based on contractual terms, for the following components of variable consideration related to product sold during the reporting period, as well as its estimate of product that remains in the distribution channel inventory of its customers at the end of the reporting period. On a quarterly basis, the Company will update its estimates and record any necessary material adjustments in the period they are identified. Chargebacks : The Company estimates chargebacks from its customers who directly purchase the product from the Company for fees and discounts resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices charged to its customers. Customers charge the Company for the difference between what they pay to the Company for the product and the selling price to the qualified healthcare providers. Reserves for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel inventories at the end of each reporting period that the Company expects will be sold to qualified healthcare providers, and chargebacks that customers have claimed, but for which the Company has not yet issued a credit. Government Rebates : The Company is subject to discount obligations under government programs, including Medicaid. The Company records reserves for rebates in the same period the related product revenue is recognized, resulting in a reduction of ZULRESSO product revenues and a current liability that is included in accrued expenses on its consolidated balance sheet. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimates of future claims that will be made for product that has been recognized as revenue, but which remains in the distribution channel at the end of each reporting period. Trade Discounts and Allowances : The Company generally provides customary invoice discounts on ZULRESSO sales to its customers for prompt payment and the Company pays fees for sales order management, data, and distribution services. The Company estimates its customers will earn these discounts and fees and deducts these discounts and fees in full from gross ZULRESSO revenues and accounts receivable at the time the Company recognizes the related revenues. Financial Assistance : The Company provides voluntary financial assistance programs to patients with commercial insurance that have coverage and reside in states that allow financial assistance. The Company estimates the average financial assistance amounts for ZULRESSO based on demographics for patients who have registered and been approved for assistance and records any such amounts within accrued expenses on its consolidated balance sheet. The calculation of the accrual for financial assistance is based on an estimate of claims and the cost per claim that the Company expects to receive associated with product that has been recognized as revenue but remains in the distribution channel at the end of each reporting period, as well as claims that have been approved but not yet paid. The adjustments are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability, which is included as a component of accrued expenses and other current liabilities on the consolidated balance sheets. Product Returns : Consistent with industry practice, the Company offers the specialty pharmacies and specialty distributors that are its customers limited product return rights for damaged, defective or expiring product, provided it is within a specified period around the product expiration date as set forth in the applicable individual distribution agreement. The Company estimates the amount of its product sales that may be returned by its customers and records this estimate as a reduction of revenue in the period the related product revenue is recognized, as well as a reserve within accrued expenses on the consolidated balance sheets. Based on the distribution model for ZULRESSO, contractual inventory limits with its customers, the product price and limited contractual return rights, the Company believe s there will be minimal ZULRESSO returns. The Company will update its estimated refund liability, on at least a quarterly basis, based on actual shipments of ZULRESSO subject to contractual return rights, changes in expectations about the amount of estimated refunds or actual returns. Inventory Inventory is stated at the lower of cost or estimated net realizable value with cost determined on a first-in, first-out basis. Inventory costs include raw materials, third-party contract manufacturing, third-party packaging services, and freight. Raw and intermediate materials that may be utilized for either research and development or commercial purposes are identical and, as a result, are both classified as inventory. Amounts in inventory associated with research and development are charged to research and development expense when the product enters the research and development process and can no longer be used for commercial purposes and, therefore, does not have an “alternative future use” as defined in authoritative guidance. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period and writes down any excess and obsolete inventory to its estimated net realizable value in the period it is identified. If they occur, such impairment charges are recorded as a component of cost of goods sold in the consolidated statements of operations and comprehensive loss. Inventory on-hand that will be sold beyond the Company's normal operating cycle is classified as non-current and grouped with other assets on the Company's consolidated balance sheets. At June 30, 2019, the Company did not have any such inventory. Prior to the initial date regulatory approval is received, costs related to the production of inventory are recorded as research and development expense on the Company’s consolidated statements of operations and comprehensive loss in the period incurred. The Company received FDA approval for ZULRESSO on March 19, 2019 and subsequently began capitalizing costs related to inventory manufacturing. Cost of Goods Sold Cost of goods sold includes direct and indirect costs related to the manufacturing and distribution of ZULRESSO, including third-party manufacturing costs, packaging services, freight, third-party royalties payable on the Company’s net product revenues and amortization of intangible assets associated with ZULRESSO. Cost of goods sold may also include period costs related to certain inventory manufacturing services, inventory adjustment charges, as well as manufacturing variances. In connection with the FDA approval of ZULRESSO on March 19, 2019, the Company subsequently began capitalizing inventory manufactured or purchased after this date. As a result, certain manufacturing costs associated with product shipments of ZULRESSO were expensed prior to FDA approval and, therefore, are not included in cost of goods sold during the current period. Accounts Receivable The Company’s trade accounts receivable consist of amounts due from specialty distributors and specialty pharmacies in the U.S. related to sales of ZULRESSO and have standard payment terms that generally require payment within 30 to 60 days from the invoice date. The Company monitors the financial performance and creditworthiness of customers so that it can properly assess and respond to changes in their credit profile. The Company reserves against trade accounts receivable for estimated losses that may arise from a customer’s inability to pay and any amounts determined to be uncollectible are written off against the reserve when it is probable that the receivable will not be collected. Trade accounts receivable are included in prepaid expenses and other current assets on the consolidated balance sheets and the amount was not significant as of June 30, 2019. Intangible assets The Company had no intangible assets as of December 31, 2018. As a result of the approval by the FDA of the New Drug Application for ZULRESSO in March 2019, the Company was required to pay to CyDex Pharmaceuticals, Inc. (“CyDex”) During the three months ended June 30, 2019, the Company began to amortize the asset and record the expense to cost of goods sold. Leases The Company determines if an arrangement is a lease at contract inception. Operating lease assets represent the Company’s right to use an underlying asset for the lease term and operating lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease assets and liabilities are recognized at the commencement date of the lease based upon the present value of lease payments over the lease term. When determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. The Company uses the implicit interest rate when readily determinable and uses the Company’s incremental borrowing rate when the implicit rate is not readily determinable based upon the information available at the commencement date in determining the present value of the lease payments. The lease payments used to determine the Company’s operating lease assets may include lease incentives, stated rent increases and escalation clauses linked to rates of inflation when determinable and are recognized in the Company’s operating lease assets in the Company’s condensed consolidated balance sheets. In addition, the Company’s contracts contain lease and non-lease components. The Company combines lease and non-lease components, which are accounted for together as lease components. The Company’s operating leases are reflected in right of use operating asset, other current liabilities and long-term lease operating liability, net of current portion in the Company’s condensed consolidated balance sheets. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. Short-term leases, defined as leases that have a lease term of 12 months or less at the commencement date, are excluded from this treatment and are recognized on a straight-line basis over the term of the lease. Recently Issued Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-02, Leases Leases (Topic 842): Targeted Improvements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which introduces a new methodology for accounting for credit losses on financial instruments, including available-for-sale debt securities. The guidance establishes a new "expected loss model" that requires entities to estimate current expected credit losses on financial instruments by using all practical and relevant information. Any expected credit losses are to be reflected as allowances rather than reductions in the amortized cost of available-for-sale debt securities. Early adoption is permitted for annual periods beginning after December 15, 2018, and interim periods therein. The Company adopted the standard on the required effective date of January 1, 2019. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures . In June 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718) – Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”), which aligns the accounting for share-based payment awards issued to employees and non-employees. Under the new guidance, the existing guidance regarding employees will apply to share-based transactions with non-employees, as long as the transaction is not effectively a form of financing, with the exception of specific guidance related to the attribution of compensation cost. The cost of non-employee awards will continue to be recorded as if the grantor had paid cash for the goods or services. In addition, the contractual term will be able to be used in lieu of an expected term in the option-pricing model for non-employee awards. The Company adopted the standard on the required effective date of January 1, 2019. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s consolidated financial statements upon adoption.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The Company’s cash equivalents are classified within Level 1 of the fair value hierarchy. The Company’s investments in marketable securities are classified within Level 2 of the fair value hierarchy. The fair values of the Company’s marketable securities are based on prices obtained from independent pricing sources. Consistent with the fair value hierarchy described above, securities with validated quotes from pricing services are reflected within Level 2, as they are primarily based on observable pricing for similar assets or other market observable inputs. Typical inputs used by these pricing services include, but are not limited to, reported trades, benchmark yields, issuer spreads, bids, offers or estimates of cash flow, prepayment spreads and default rates. The following tables summarize the Company’s money market funds and marketable securities as of June 30, 2019 and December 31, 2018. June 30, 2019 Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in thousands) Cash equivalents: Cash equivalents $ 166,185 $ 166,185 $ — $ — Total cash equivalents 166,185 166,185 — — Marketable securities: U.S. government securities 290,571 — 290,571 — U.S. corporate bonds 478,806 — 478,806 — International corporate bonds 147,470 — 147,470 — U.S. commercial paper 107,099 — 107,099 — International commercial paper 46,418 — 46,418 — Total marketable securities 1,070,364 — 1,070,364 — $ 1,236,549 $ 166,185 $ 1,070,364 $ — December 31, 2018 Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in thousands) Cash equivalents: Cash equivalents $ 190,943 $ 190,943 $ — $ — Total cash equivalents 190,943 190,943 — — Marketable securities: U.S. government securities 220,482 — 220,482 — U.S. corporate bonds 258,566 — 258,566 — International corporate bonds 78,468 — 78,468 — U.S. commercial paper 77,611 — 77,611 — International commercial paper 96,706 — 96,706 — Total marketable securities 731,833 — 731,833 — $ 922,776 $ 190,943 $ 731,833 $ — During the six months ended June 30, 2019 and 2018, there were no transfers among the Level 1, Level 2 and Level 3 categories. The following tables summarize the gross unrealized gains and losses of the Company’s marketable securities as of June 30, 2019 and December 31, 2018: June 30, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Assets: U.S. government securities $ 290,271 $ 302 $ (2 ) $ 290,571 U.S. corporate bonds 477,932 942 (68 ) 478,806 International corporate bonds 147,062 434 (26 ) 147,470 U.S. commercial paper 107,105 1 (7 ) 107,099 International commercial paper 46,419 — (1 ) 46,418 $ 1,068,789 $ 1,679 $ (104 ) $ 1,070,364 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Assets: U.S. government securities $ 220,531 $ 8 $ (57 ) $ 220,482 U.S. corporate bonds 258,876 6 (316 ) 258,566 International corporate bonds 78,600 — (132 ) 78,468 U.S. commercial paper 77,630 8 (27 ) 77,611 International commercial paper 96,711 8 (13 ) 96,706 $ 732,348 $ 30 $ (545 ) $ 731,833 As of June 30, 2019, all marketable securities, except for 48 bonds with a fair value of $185.0 million that have maturities of between one and two years, held by the Company had remaining contractual maturities of one year or less. As of December 31, 2018, all marketable securities, except for two U.S. corporate bonds, held by the Company had remaining contractual maturities of one year or less. There have been no impairments of the Company’s assets measured and carried at fair value during the six months ended June 30, 2019 and the year ended December 31, 2018.

Balance Sheet Components

Balance Sheet Components	6 Months Ended
	Jun. 30, 2019
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	4. Balance Sheet Components Property and Equipment, net Property and equipment, net, consists of the following: June 30, December 31, 2019 2018 (in thousands) Computer hardware and software $ 2,427 $ 2,148 Furniture and equipment 1,774 1,002 Leasehold improvements 7,298 4,709 11,499 7,859 Less: Accumulated depreciation (3,136 ) (2,216 ) $ 8,363 $ 5,643 Depreciation expense for the three months ended June 30, 2019 and 2018 was $0.5 million and $0.2 million, respectively. Depreciation expense for the six months ended June 30, 2019 and 2018 was $0.9 million and $0.5 million, respectively. The useful life for computer hardware and software is three years, furniture and equipment is five years and leasehold improvements is the lesser of the useful life or the term of the respective lease. Accrued Expenses Accrued expenses consist of the following: June 30, December 31, 2019 2018 (in thousands) Development costs $ 28,498 $ 21,216 Employee-related expenses 15,585 19,638 Professional services 14,299 10,903 Other accrued expenses 530 237 $ 58,912 $ 51,994

Leases, Commitments and Conting

Leases, Commitments and Contingencies	6 Months Ended
	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Leases, Commitments and Contingencies	5. Leases, Commitments and Contingencies Operating Leases The Company has leases for office space, vehicles, and certain equipment. All of the leases recorded on the balance sheet are operating leases. The Company’s leases have remaining lease terms ranging from less than one year to approximately six years. Some of the leases include options to extend the leases for up to five years and these options were not included for the purpose of determining the right-of-use assets and associated lease liabilities as the Company determined that the renewal of these leases is not reasonably certain so only the original lease term was taken into consideration. The leases do not include any restrictions or covenants that had to be accounted for under the lease guidance. The Company leases office space in two multi-tenant buildings in Cambridge, Massachusetts, consisting, as of June 30, 2019, of 63,017 square feet in the first building under an operating lease that will expire on August 31, 2024 and 19,805 square feet in the second building under an operating lease that will expire on August 31, 2024. In April 2018, the Company entered into the First Amendment to the lease for office space in the second multi-tenant building and thereby increased the amount of square feet of office space from 19,805 square feet to 40,419 square feet, an increase of 20,614 square feet, consisting of (i) 13,481 square feet that began on August 1, 2018, and (ii) 7,133 square feet that began on October 1, 2018. The term for this additional space will expire on August 31, 2024. Additionally, the term of the existing lease was extended from February 28, 2022 until August 31, 2024. In May 2018, the Company entered into a lease for office space in a multi-tenant building in Raleigh, North Carolina. The amount of square feet of office space is 15,525 square feet and the lease period began on September 1, 2018. The term for this space will expire on November 30, 2024. In October 2018, the Company entered into the Seventh Amendment to the lease for office space in the first building and thereby increased the amount of square feet of office space from 54,943 square feet to 58,442 In December 2018, the Company entered into a lease in a third multi-tenant building in Cambridge, Massachusetts, for 15,975 square feet of office space which began on March 1, 2019. The term for this lease will expire on February 28, 2024. In March 2019, the Company entered into the Eighth Amendment to the lease for office space in the first building and thereby increased the amount of square feet of office space from 58,442 square feet to 63,017 square feet. The increase of 4,575 square feet began on June 1, 2019. The term for this additional space will expire on August 31, 2024. The following table summarizes the presentation in the Company’s condensed consolidated balance sheets of operating leases: (In thousands) Balance sheet location As of June 30, 2019 Assets Right of use operating asset Right of use operating asset $ 37,224 Liabilities Current operating lease liabilities Other current liabilities 7,393 Long-term operating lease liabilities Long-term lease operating liability, net of current portion 33,309 Total operating lease liabilities $ 40,702 The following table summarizes the effect of lease costs in the Company’s condensed consolidated statements of operations and comprehensive loss: Three Months Ended Six Months Ended (In thousands) June 30, 2019 June 30, 2019 Operating lease cost $ 2,436 $ 4,880 The Company made an accounting policy election not to apply the recognition requirements to short-term leases. The Company recognizes the lease payments for short-term leases in profit or loss on a straight-line basis over the lease term, and variable lease payments in the period in which the obligation for those payments is incurred. For the three and six months ended June 30, 2019, the Company recorded $0.1 million and $0.3 million of expense for its short-term leases, respectively. The minimum lease payments are expected to be as follows: Years Ending December 31, (in thousands) 2019 (remaining six months) $ 5,080 2020 10,244 2021 9,972 2022 8,898 2023 9,105 Thereafter 5,560 Total lease payments 48,859 Less imputed interest (8,157 ) Present value of operating lease liabilities $ 40,702 Under the prior lease guidance, future minimum lease payments under non-cancelable operating leases were as follows at December 31, 2018: Years Ending December 31, (in thousands) 2019 $ 7,918 2020 8,299 2021 8,463 2022 8,692 2023 8,894 Thereafter 5,415 $ 47,681 The weighted average remaining lease term and weighted average discount rate of the Company’s operating leases are as follows: As of June 30, 2019 Weighted average remaining lease term in years 4.86 Weighted average discount rate 7.5% The interest rate implicit in lease contracts is typically not readily determinable and as such, the Company uses its incremental borrowing rate based on the information available at the lease commencement date, which represents an internally developed rate that would be incurred to borrow, on a collateralized basis, over a similar term, an amount equal to the lease payments in a similar economic environment. Supplemental disclosure of cash flow information related to the Company’s operating leases included in cash flows used by operating activities in the condensed consolidated statements of cash flows is as follows: Three Months Ended Six Months Ended (In thousands) June 30, 2019 June 30, 2019 Cash paid for amounts included in the measurement of lease liabilities $ 2,513 $ 4,867 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ 872 $ 872 During the three and six months ended June 30, 2019, other than the initial adoption of the lease standard that required right of use assets and lease liabilities to be recorded, one right of use asset was recorded arising from new lease liabilities. In March 2019, the Company entered into the Eighth Amendment to the lease for office space in the first building and thereby increased the amount of square feet of office space from 58,442 square feet to 63,017 square feet. The increase of 4,575 square feet began on June 1, 2019. The term for this additional space will expire on August 31, 2024. License Agreements CyDex License Agreement In September 2015, the Company and CyDex amended and restated their existing commercial license agreement. Under the terms of the commercial license agreement as amended and restated, CyDex has granted to the Company an exclusive license to CyDex’s Captisol drug formulation technology and related intellectual property for the manufacture of pharmaceutical products incorporating brexanolone and the Company’s compound known as SAGE-689, and the development and commercialization of the resulting products in the treatment, prevention or diagnosis of any disease or symptom in humans or animals other than (i) the ocular treatment of any disease or condition with a formulation, including a hormone; (ii) topical ocular treatment of inflammatory conditions; (iii) treatment and prophylaxis of fungal infections in humans; and (iv) any ocular treatment for retinal degeneration. The Company is required to pay a royalty to CyDex on sales of brexanolone and will be required to pay a royalty on sales of SAGE-689, if successfully developed in the future The Company is obligated to make milestone payments under the amended and restated license agreement with CyDex based on the achievement of clinical development and regulatory milestones in the amount of up to $0.8 million in clinical milestones and up to $3.8 million in regulatory milestones for each of the first two fields with respect to brexanolone; up to $1.3 million in clinical milestones and up to $8.5 million in regulatory milestones for each of the third and fourth fields with respect to brexanolone; and up to $0.8 million in clinical milestones and up to $1.8 million in regulatory milestones for one field with respect to SAGE-689. As of June 30, 2019, the Company has recorded research and development expense and made cash payments of $2.3 million related to these clinical development and regulatory milestones; and has recorded an intangible asset and made a cash payment of $3.0 million. For the three months ended June 30, 2019, the Company did not record any expense or intangible asset, or make any milestone payments related to clinical development or regulatory milestones for the brexanolone program under the license agreement with CyDex. For the six months ended June 30, 2019, the Company recorded an intangible asset and made a cash payment of $3.0 million related to a regulatory milestone for the brexanolone program under the license agreement with CyDex. For the three and six months ended June 30, 2018, the Company recorded research and development expense and made cash payments of $0.8 million related to regulatory milestones for the brexanolone program under the license agreement with CyDex. University of California License Agreements In October 2013, the Company entered into a non-exclusive license agreement with The Regents of the University of California under which the Company was granted a non-exclusive license to certain clinical data and clinical material related to brexanolone for use in the development and commercialization of biopharmaceutical products in the licensed field, including status epilepticus and postpartum depression. In May 2014, the license agreement was amended to add the treatment of essential tremor to the licensed field of use, materials and milestone fee provisions of the agreement. As of December 31, 2015, the Company paid to The Regents of the University of California clinical development milestones of $0.1 million. The Company is required to pay royalties of less than 1% on net sales for a period of fifteen years following the sale of the first product developed using the data and materials. The license will terminate on the earlier to occur of (i) 27 years after the effective date or (ii) 15 years after the last-derived product is first commercially sold. In June 2015, the Company entered into an exclusive license agreement with The Regents of the University of California whereby the Company was granted an exclusive license to certain patent rights related to the use of allopregnanolone to treat various diseases. In exchange for such license, the Company paid an upfront payment of $50,000 and will make payments of $15,000 for annual maintenance fees until the calendar year following the first sale, if any, of a licensed product. The Company is obligated to make milestone payments following the achievement of specified regulatory and sales milestones of up to $0.7 million and $2.0 million in the aggregate, respectively. Following the first sale of a licensed product, the Company is required to pay royalties at a low single digit percentage of net sales of licensed products, subject to specified minimum annual royalty amounts. Unless terminated by operation of law or by acts of the parties under the terms of the agreement, the license agreement will terminate when the last-to-expire patents or last-to-be abandoned patent applications expire, whichever is later. As of June 30, 2019, the Company has recorded research and development expense and made cash payments of $0.3 million related to these regulatory and sales milestones; and has recorded an intangible asset and made a cash payment of $0.5 million related to these regulatory and sales milestones. For the three months ended June 30, 2019, the Company did not record any expense or make any milestone payments under either license agreement with The Regents of the University of California. For the six months ended June 30, 2019, the Company recorded an intangible asset and made a cash payment of $0.5 million related to a regulatory milestone under the license agreements with The Regents of the University of California. For the three and six months ended June 30, 2018, the Company recorded research and development expense and made cash payments of $0.2 million related to regulatory milestones under the license agreements with The Regents of the University of California. Washington University License Agreement In November 2013, the Company entered into a license agreement with Washington University whereby the Company was granted exclusive, worldwide rights to develop and commercialize a novel set of neuroactive steroids developed by Washington University. In exchange for development and commercialization rights, the Company paid an upfront, non-refundable payment of $50,000 and is required to pay an annual license maintenance fee of $15,000 on each subsequent anniversary date, until the first Phase 2 clinical trial for a licensed product is initiated. The Company is obligated to make milestone payments to Washington University based on achievement of clinical development and regulatory milestones of up to $0.7 million and $0.5 million, respectively. Additionally, the Company fulfilled its obligation to issue to Washington University 47,619 shares of common stock on December 13, 2013. The fair value of these shares of $0.1 million was recorded as research and development expense in 2013. As of June 30, 2019, the Company has recorded research and development expense and made a cash payment of $50,000 related to these clinical and development milestones. The Company is obligated to pay royalties to Washington University at rates in the low single digits on net sales of licensed products covered under patent rights and royalties at rates in the low single digits on net sales of licensed products not covered under patent rights. Additionally, the Company has the right to sublicense and is required to make payments at varying percentages of sublicensing revenue received, initially in the mid-teens and descending to the mid-single digits over time. For the three and six months ended June 30, 2019 and 2018, the Company did not record any expense or make any milestone payments under the license agreement with Washington University. Consulting Agreement In January 2014, the Company entered into a consulting agreement with a then non-employee advisor whereby the Company is obligated to make cash payments of up to $2.0 million and to issue up to 126,984 shares of common stock upon attainment of certain clinical development and regulatory milestones. As of June 30, 2019, the Company recorded research and development expense of $1.8 million, comprised of $0.5 million in cash and $1.3 million related to the issuance of 39,681 shares of the Company’s common stock, related to the achievement of these milestones. For the three and six months ended June 30, 2019 and 2018, the Company did not record any expense or make any milestone payments under the consulting agreement with the non-employee advisor.

Collaborative Agreement

Collaborative Agreement	6 Months Ended
	Jun. 30, 2019
Collaboration Agreement [Abstract]
Collaborative Agreement	6. Collaboration Agreement Effective June 12, 2018, the Company entered into a strategic collaboration with Shionogi for the clinical development and commercialization of SAGE-217 for the treatment of major depressive disorder (“MDD”) and other potential indications in Japan, Taiwan and South Korea. Under the terms of the agreement, Shionogi will be responsible for all clinical development, regulatory filings and commercialization of SAGE-217 for MDD, and potentially other indications, in Japan, Taiwan and South Korea. Shionogi was required to make an upfront payment to the Company of $90.0 million, and the Company will be eligible to receive additional payments of up to $485.0 million if certain regulatory and commercial milestones are achieved by Shionogi. The potential future milestone payments include up to $70.0 million for the achievement of specified regulatory milestones, up to $30.0 million for the achievement of specified commercialization milestones, and up to $385.0 million for the achievement of specified net sales milestones. Due to the uncertainty of pharmaceutical development and the high historical failure rates generally associated with drug development, the Company may not receive any additional milestone payments or any royalty payments from Shionogi. The Company concluded that Shionogi meets the definition to be accounted for as a customer since the Company is delivering intellectual property and know-how rights for the SAGE-217 program in support of territories in which the parties are not jointly sharing the risks and rewards. In addition, the Company determined that the Shionogi collaboration met the requirements to be accounted for as a contract, including that it was probable that the Company will collect the consideration related to the up-front payment to which the Company was entitled in exchange for the goods or services that will be delivered to Shionogi. In determining the appropriate amount of revenue to be recognized under ASC 606, the Company performed the following steps: (i) identified the promised goods or services in the contract; (ii) determined whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measured the transaction price, including the constraint on variable consideration; (iv) allocated the transaction price to the performance obligations; and (v) recognized revenue when (or as) the Company satisfies each performance obligation. The Company determined that the performance obligations included the license to SAGE-217, supply of certain clinical materials and manufacturing supply of the active pharmaceutical ingredient (“API”). The performance obligation related to the license to SAGE-217 was determined to be distinct from other performance obligations and therefore was a standalone performance obligation for which control was transferred upon signing. The obligation to provide certain clinical materials was determined to be a separate performance obligation. The agreement related to supplying API was determined to be an option for Shionogi to purchase, rather than a firm obligation since no minimum amount or quantities are specified and, therefore, was not considered a performance obligation within the main agreement. Given this fact pattern, the Company has concluded the agreement has two performance obligations. The Company completed the evaluation of the standalone selling prices of each of the performance obligations and determined that the standalone selling price of the license performance obligation was $90.0 million. The Company recognized the transaction price allocated to the license performance obligation of $90.0 million as revenue during the quarter upon delivery of the license to Shionogi and resulting ability of Shionogi to use and benefit from the license. The remaining transaction price related to the performance obligation for the supply of certain clinical material is not significant. The potential milestone payments that the Company is eligible to receive were excluded from the transaction price, as all milestone amounts were fully constrained based on the probability of achievement. The Company will reevaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, if necessary, adjust its estimate of the transaction price.

Sale of Equity Securities

Sale of Equity Securities	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Sale of Equity Securities	7. Sale of Equity Securities On February 13, 2018, the Company completed the sale of 4,032,012 shares of its common stock in an underwritten public offering at a price to the public of $164.00 per share, resulting in net proceeds of $631.2 million after deducting commissions and underwriting discounts and offering costs paid by the Company. On February 27, 2019, the Company completed the sale of 3,833,334 shares of its common stock in an underwritten public offering at a price to the public of $150.00 per share, resulting in net proceeds of $560.9 million after deducting commissions and underwriting discounts and offering costs paid by the Company.

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation Restricted Stock Units During the three months ended March 31, 2017, the Company granted 32,500 restricted stock units to certain employees of the Company. The Company did not grant restricted stock units prior to January 1, 2017. These restricted stock units vest ratably over two years, with cliff vesting of 50% at both the one-year and two-year anniversary of the grant date, which was in February 2018 and February 2019, respectively. During the three months ended March 31, 2018, the Company granted 33,600 performance restricted stock units to certain employees of the Company. The milestones for these grants were not met, and accordingly, these grants were cancelled. During the three months ended June 30, 2018, the Company granted 37,800 performance restricted stock units to certain employees of the Company. These performance restricted stock units will vest upon the achievement of a certain commercial milestone. During the three and six months ended June 30, 2019, the Company granted 16,345 and 370,456, performance restricted stock units, respectively, to employees of the Company. These performance restricted stock units will vest upon the achievement of a certain clinical and regulatory development milestones related to product candidates and a commercial milestone. The fair value of restricted stock units that vested during the six months ended June 30, 2019 and 2018 was $2.0 million and $2.6 million, respectively. No restricted stock units vested during the three months ended June 30, 2019 and 2018. The table below summarizes activity relating to restricted stock units: Shares Outstanding as of December 31, 2018 82,700 Granted 370,456 Vested (13,250 ) Forfeited (43,240 ) Outstanding as of June 30, 2019 396,666 Stock Option Plans On July 2, 2014, the stockholders of the Company approved the 2014 Stock Option and Incentive Plan (the “2014 Stock Option Plan”), which became effective immediately prior to the completion of the Company’s IPO. The 2014 Stock Option Plan provides for the grant of restricted stock awards, restricted stock units, incentive stock options and non-statutory stock options. The 2014 Stock Option Plan replaced the Company’s 2011 Stock Option and Grant Plan (the “2011 Stock Option Plan”). The Company no longer grants stock options or other awards under its 2011 Stock Option Plan, but any options or awards outstanding under the 2011 Stock Option Plan remain outstanding and effective. The 2014 Stock Option Plan provides for an annual increase, to be added on the first day of each fiscal year, by up to 4% of the Company’s outstanding shares of common stock as of the last day of the prior year. On January 1, 2019, 1,875,530 shares of common stock, representing 4% of the Company’s outstanding shares of common stock as of December 31, 2018, were added to the 2014 Stock Option Plan. On December 15, 2016, the Board of Directors of the Company (the “Board”) approved the 2016 Inducement Equity Plan (the “2016 Stock Option Plan”). The 2016 Stock Option Plan provides for the grant of equity awards to individuals who have not previously been an employee or a non-employee director of the Company to induce them to accept employment and to provide them with a proprietary interest in the Company. On September 20, 2018, the Board amended the 2016 Stock Option Plan to increase the total number of shares reserved for issuance under such plan by 1,200,000 shares. As of June 30, 2019, the total number of shares reserved under all equity plans was 11,045,846, and 2,781,281 shares were available for future issuance under such plans. During the three and six months ended June 30, 2018, the Company granted 200,250 and 524,003 options, respectively, to employees to purchase shares of common stock that contain performance-based vesting criteria, primarily related to the achievement of certain clinical and regulatory development milestones related to product candidates and a commercial milestone. Recognition of stock-based compensation expense associated with these performance-based stock options commences when the performance condition is considered probable of achievement, using management’s best estimates, which consider the inherent risk and uncertainty regarding the future outcomes of the milestones. During the six months ended June 30, 2019, the Company granted no options to employees to purchase shares of common stock that contain performance-based vesting criteria. During the three months ended March 31, 2019, the achievement of one un-met commercial milestone that is the criteria for vesting of performance-based stock options was considered probable, and therefore $14.2 million of stock-based compensation expense was recognized related to these awards for the three months ended March 31, 2019. Stock options with this milestone were granted during the years ended December 31, 2018 and 2017. During the three months ended June 30, 2019, this commercial milestone was achieved. This milestone represents 20% and 33% of the performance-based option grants that were made during the years ended December 31, 2018 and 2017, respectively. During the three months ended June 30, 2019, the Company recognized stock-based compensation expense related to this milestone of $2.1 million. During the six months ended June 30, 2019, the Company recognized stock-based compensation expense related to this milestone of $16.3 million. As of June 30, 2018, for grants that were outstanding, the achievement of the milestones that had not been met that are the criteria for vesting of performance-based stock options was considered not probable, and therefore no expense had been recognized related to these awards for the six months ended June 30, 2018. As of June 30, 2019, for grants that were outstanding, the achievement of the milestones that had not been met that are the criteria for vesting of performance-based stock options was considered not probable, and therefore no expense had been recognized related to these awards for the three months ended June 30, 2019. During the three months ended June 30, 2018, a performance milestone was achieved under a stock option granted to a consultant. The milestone was related to the consummation of a licensing or corporate partnering arrangement. During the three months ended June 30, 2018, the Company recognized stock-based compensation expense related to this milestone of $6.9 million. Stock-based compensation expense for stock options, restricted stock units and the employee stock purchase plan recognized during the three and six months ended June 30, 2019 and 2018 was as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (in thousands) Research and development $ 13,672 $ 12,095 $ 34,417 $ 20,994 Selling, general and administrative 21,095 16,933 44,466 23,851 $ 34,767 $ 29,028 $ 78,883 $ 44,845 Stock-based compensation expense by award type recognized during the three and six months ended June 30, 2019 and 2018 was as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (in thousands) Stock options $ 34,280 $ 28,627 $ 77,844 $ 44,007 Restricted stock units — 155 58 324 Employee stock purchase plan 487 246 981 514 $ 34,767 $ 29,028 $ 78,883 $ 44,845 The weighted average grant date fair value per share of stock options granted under the Company’s stock option plans during the six months ended June 30, 2019 and 2018 was $99.11 and $114.72, respectively. The table below summarizes activity related to stock options: Shares Weighted Average Exercise Price Weighted Average Remaining Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2018 7,530,767 $ 93.22 8.03 $ 227,447 Granted 1,355,931 — Exercised (745,558 ) — Forfeited (281,850 ) — Outstanding as of June 30, 2019 7,859,290 $ 107.81 7.98 $ 600,965 Exercisable as of June 30, 2019 3,321,049 $ 70.02 6.89 $ 378,713 At June 30, 2019, the Company had unrecognized stock-based compensation expense related to its unvested service-based stock option awards of $310.7 million, which is expected to be recognized over the remaining weighted average vesting period of 2.74 years. The intrinsic value of stock options exercised during the six months ended June 30, 2019 and 2018 was $87.4 million and $64.4 million, respectively. At June 30, 2019, 505,131 performance-based stock options were both outstanding and unvested, and the total unrecognized stock-based compensation expense related to those awards was $35.2 million.

Net Loss Per Share

Net Loss Per Share	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Net Loss Per Share	9. Net Loss Per Share Basic and diluted net loss per share was calculated as follows for the three and six months ended June 30, 2019 and 2018: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Basic net loss per share: Numerator: Net loss (in thousands) $ (168,221 ) $ (16,978 ) $ (331,627 ) $ (91,576 ) Denominator: Weighted average common stock outstanding - basic 51,257,640 46,541,716 49,882,377 45,439,666 Dilutive effect of shares of common stock equivalents resulting from common stock options and restricted stock units — — — — Weighted average common stock outstanding - diluted 51,257,640 46,541,716 49,882,377 45,439,666 Net loss per share—basic and diluted $ (3.28 ) $ (0.36 ) $ (6.65 ) $ (2.02 ) The following common stock equivalents outstanding as of June 30, 2019 and 2018 were excluded from the calculation of diluted net loss per share for the periods presented because including them would have been anti-dilutive: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Stock options 7,362,768 6,207,172 7,362,768 6,207,172 Restricted stock units — 13,950 — 13,950 Employee stock purchase plan 39,006 8,004 39,006 8,004 7,401,774 6,229,126 7,401,774 6,229,126 Stock options and restricted stock units that are outstanding and contain performance-based vesting criteria for which the performance conditions have not been met are excluded from the calculation of common stock equivalents outstanding.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The unaudited interim condensed consolidated financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these unaudited condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2018, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements. In the opinion of the Company’s management, the accompanying unaudited condensed consolidated financial statements contain all adjustments, consisting of only normal recurring adjustments, necessary for a fair statement of its financial position as of June 30, 2019, its results of operations and comprehensive loss for the three and six months ended June 30, 2019 and 2018, its cash flows for the six months ended June 30, 2019 and 2018, and its statements of changes in stockholders’ equity for the six months ended June 30, 2019 and 2018. The consolidated balance sheet at December 31, 2018 was derived from audited financial statements, but does not include all disclosures required by GAAP. The results for the three and six months ended June 30, 2019 are not necessarily indicative of the results for the year ending December 31, 2019, or for any future period.
Principles of Consolidation	Principles of Consolidation The unaudited interim condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries as disclosed in Note 2, Summary of Significant Accounting Policies, within the “Notes to Consolidated Financial Statements” accompanying its Annual Report on Form 10-K for the fiscal year ended December 31, 2018. Intercompany accounts and transactions have been eliminated.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Research and Development	Research and Development Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries and benefits, overhead costs, depreciation, contract services and other related costs. Research and development costs are expensed to operations as the related obligation is incurred. The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the U.S. These agreements are generally cancelable, and related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by the Company. The historical accrual estimates made by the Company have not been materially different from the actual costs.
Stock-Based Compensation	Stock-Based Compensation The Company recognizes compensation expense for stock-based awards, including grants of stock options and restricted stock, made to employees and non-employee directors based on the estimated fair value on the date of grant, over the requisite service period. Effective January 1, 2019, the Company recognizes compensation expense for stock-based awards, including grants of stock options and restricted stock, made to non-employee consultants based on the estimated fair value on the date of grant, over the requisite service period. Through December 31, 2018, the Company recognized compensation expense for stock-based awards granted to non-employee consultants based on the fair value of the awards on each date on which the awards vest. Compensation expense was recognized over the vesting period, provided that services were rendered by such non-employee consultants during that time. At the end of each financial reporting period, the fair value of unvested options was re-measured using the then-current fair value of the common stock of the Company and updated assumptions in the Black-Scholes option-pricing model. For awards that vest upon achievement of a performance condition, the Company recognizes compensation expense when achievement of the performance condition is met or during the period from which meeting the condition is deemed probable until the expected date of meeting the performance condition. The fair value of each option grant is estimated using the Black-Scholes option-pricing model. Through December 31, 2015, the Company lacked sufficient Company-specific historical and implied volatility information, and as a result, the Company used the volatility of a group of publicly-traded peer companies in the Black-Scholes calculations. Beginning in 2016, the Company estimated its expected volatility using a weighted average of the historical volatility of publicly-traded peer companies and the volatility of its common stock and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its traded stock price for the duration of the expected term. The expected term of the options granted to employees and non-employee directors by the Company has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. Through December 31, 2018, the expected term of its options granted to non-employee consultants has been determined based on the contractual term of the options, and effective January 1, 2019, the “simplified” method is used. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. The expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The Company also applies a forfeiture rate in order to calculate stock-based compensation expense. Expected forfeitures are based on the historical experience of the Company and management’s expectations of future forfeitures. To the extent actual forfeitures differ from the estimates, the difference is recorded as a cumulative adjustment in the period in which the estimates are revised. The Company recognizes stock-based compensation expense for only the portion of awards that are expected to vest.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of 90 days or less at the date of purchase to be cash equivalents. As of June 30, 2019 and December 31, 2018, cash equivalents were comprised of cash equivalents and money market funds.
Marketable Securities	Marketable securities Marketable securities consist of investments with original maturities greater than 90 days. The Company has classified its investments with maturities beyond one year as short-term, based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. The Company considers its investment portfolio of investments to be available-for-sale. Accordingly, these investments are recorded at fair value, which is based on quoted market prices. Unrealized gains and losses are reported as a component of accumulated other comprehensive items in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other expense, net, based on the specific identification method. When determining whether a decline in value is other than temporary, the Company considers several factors, including whether the Company has the intent to sell the security, and whether it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis. No declines in value were deemed to be other than temporary during the three and six months ended June 30, 2019 and 2018.
Fair Value Measurements	Fair Value Measurements Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Financial assets and liabilities carried at fair value are classified and disclosed in one of the following three categories: Level 1 — Quoted market prices in active markets for identical assets or liabilities. Level 2 — Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The Company’s cash equivalents and marketable securities at June 30, 2019 and December 31, 2018 were carried at fair value, determined according to the fair value hierarchy; see Footnote 3, Fair Value Measurements herein. The carrying amounts reflected in the unaudited condensed consolidated balance sheets for accounts payable and accrued expenses approximate their fair values due to their short-term maturities at June 30, 2019 and December 31, 2018, respectively.
Revenue Recognition	Revenue Recognition Effective January 1, 2017, the Company adopted Accounting Standards Codification (“ASC”), Topic 606, Revenue from Contracts with Customers The Company received approval of ZULRESSO from the FDA in March 2019 and subsequently began to record revenues from product sales in June 2019. Prior to the second quarter of 2019, all of the revenues of the Company were derived from the Company’s collaboration agreement with Shionogi & Co., Ltd., (“Shionogi”). The terms of the Company’s collaboration agreement include consideration such as non-refundable license fees, funding of research and development services, payments due upon the achievement of clinical and pre-clinical performance-based development milestones, regulatory milestones, manufacturing services to supply drug product for clinical trials, and sales-based milestones and royalties on product sales. Under Topic 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price, including variable consideration, if any; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. For contracts determined to be within the scope of Topic 606, the Company assesses whether the goods or services promised within each contract are distinct to identify those that are performance obligations. This assessment involves subjective determinations and requires management to make judgments about the individual promised goods or services and whether such are separable from the other aspects of the contractual relationship. Promised goods and services are considered distinct provided that: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. The Company allocates the transaction price (the amount of consideration it expects to be entitled to from a customer in exchange for the promised goods or services) to each performance obligation and recognizes the associated revenue when (or as) each performance obligation is satisfied. The Company’s estimate of the transaction price for each contract includes all variable consideration to which the Company expects to be entitled. Collaboration and license revenue In assessing whether a promised good or service is distinct in the evaluation of a collaboration or license arrangement subject to Topic 606, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. The Company also considers the intended benefit of the contract in assessing whether a promised good or service is separately identifiable from other promises in the contract. If a promised good or service is not distinct, the Company is required to combine that good or service with other promised goods or services until it identifies a bundle of goods or services that is distinct. The transaction price is then determined and allocated to the identified performance obligations in proportion to their standalone selling prices (“SSP”) on a relative SSP basis. SSP is determined at contract inception and is not updated to reflect changes between contract inception and when the performance obligations are satisfied. Determining the SSP for performance obligations requires significant judgment. In developing the SSP for a performance obligation, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. In certain circumstances, the Company may apply the residual method to determine the SSP of a good or service if the standalone selling price is considered highly variable or uncertain. The Company validates the SSP for performance obligations by evaluating whether changes in the key assumptions used to determine the SSP will have a significant effect on the allocation of arrangement consideration between multiple performance obligations. If an arrangement includes development and regulatory milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. In determining the transaction price, the Company adjusts consideration for the effects of the time value of money if the timing of payments provides the Company with a significant benefit of financing. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. The Company assessed its arrangement with Shionogi and concluded that a significant financing component does not exist. For arrangements with licenses of intellectual property that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes royalty revenue and sales-based milestones at the later of (i) when the related sales occur, or (ii) when the performance obligation to which the royalty has been allocated has been satisfied. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) each performance obligation is satisfied at a point in time or over time, and if over time this is based on the use of an output or input method. To date, revenue from the Company’s collaboration agreement with Shionogi has come from an initial, up-front fee upon execution of the agreement and payment for the supply of SAGE-217 drug product for Shionogi clinical trials. Product revenue The Company recognizes product revenues, net of variable consideration related to certain allowances and accruals that are determined using the expected value method, in its consolidated financial statements at the point in time when delivery is made and when control transfers to the customer, which is typically when the product has been delivered to the customer’s location. The amount included in the transaction price is constrained to the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. The Company’s only performance obligation identified for ZULRESSO is to deliver the product to the location specified by the customer’s order. The Company records shipping and handling costs associated with delivery of product to its customers within selling, general and administrative expenses on its consolidated statements of operations and comprehensive loss. The Company expense s incremental costs of obtaining a contract as incurred if the expected amortization period of the asset would be less than one year. I f the C ompany were to incur incremental costs with an amortization period greater than a year, such costs would be capitalized as contract assets, as they are expected to be recovered , and would be expensed by amortizing on a systematic basis that is consistent with the transfer to the customer of the goods or services to which the asset relates . The Company did not have any contract assets (unbilled receivables) at June 30, 2019, as customer invoicing generally occurs before or at the time of revenue recognition. The Company did not have any contract liabilities at June 30, 2019, as the Company did not receive any payments in advance of satisfying its performance obligations to its customers. Amounts billed or invoiced are included in prepaid expenses and other current assets on the consolidated balance sheets. The Company records reserves, based on contractual terms, for the following components of variable consideration related to product sold during the reporting period, as well as its estimate of product that remains in the distribution channel inventory of its customers at the end of the reporting period. On a quarterly basis, the Company will update its estimates and record any necessary material adjustments in the period they are identified. Chargebacks : The Company estimates chargebacks from its customers who directly purchase the product from the Company for fees and discounts resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices charged to its customers. Customers charge the Company for the difference between what they pay to the Company for the product and the selling price to the qualified healthcare providers. Reserves for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel inventories at the end of each reporting period that the Company expects will be sold to qualified healthcare providers, and chargebacks that customers have claimed, but for which the Company has not yet issued a credit. Government Rebates : The Company is subject to discount obligations under government programs, including Medicaid. The Company records reserves for rebates in the same period the related product revenue is recognized, resulting in a reduction of ZULRESSO product revenues and a current liability that is included in accrued expenses on its consolidated balance sheet. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimates of future claims that will be made for product that has been recognized as revenue, but which remains in the distribution channel at the end of each reporting period. Trade Discounts and Allowances : The Company generally provides customary invoice discounts on ZULRESSO sales to its customers for prompt payment and the Company pays fees for sales order management, data, and distribution services. The Company estimates its customers will earn these discounts and fees and deducts these discounts and fees in full from gross ZULRESSO revenues and accounts receivable at the time the Company recognizes the related revenues. Financial Assistance : The Company provides voluntary financial assistance programs to patients with commercial insurance that have coverage and reside in states that allow financial assistance. The Company estimates the average financial assistance amounts for ZULRESSO based on demographics for patients who have registered and been approved for assistance and records any such amounts within accrued expenses on its consolidated balance sheet. The calculation of the accrual for financial assistance is based on an estimate of claims and the cost per claim that the Company expects to receive associated with product that has been recognized as revenue but remains in the distribution channel at the end of each reporting period, as well as claims that have been approved but not yet paid. The adjustments are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability, which is included as a component of accrued expenses and other current liabilities on the consolidated balance sheets. Product Returns : Consistent with industry practice, the Company offers the specialty pharmacies and specialty distributors that are its customers limited product return rights for damaged, defective or expiring product, provided it is within a specified period around the product expiration date as set forth in the applicable individual distribution agreement. The Company estimates the amount of its product sales that may be returned by its customers and records this estimate as a reduction of revenue in the period the related product revenue is recognized, as well as a reserve within accrued expenses on the consolidated balance sheets. Based on the distribution model for ZULRESSO, contractual inventory limits with its customers, the product price and limited contractual return rights, the Company believe s there will be minimal ZULRESSO returns. The Company will update its estimated refund liability, on at least a quarterly basis, based on actual shipments of ZULRESSO subject to contractual return rights, changes in expectations about the amount of estimated refunds or actual returns.
Inventory	Inventory Inventory is stated at the lower of cost or estimated net realizable value with cost determined on a first-in, first-out basis. Inventory costs include raw materials, third-party contract manufacturing, third-party packaging services, and freight. Raw and intermediate materials that may be utilized for either research and development or commercial purposes are identical and, as a result, are both classified as inventory. Amounts in inventory associated with research and development are charged to research and development expense when the product enters the research and development process and can no longer be used for commercial purposes and, therefore, does not have an “alternative future use” as defined in authoritative guidance. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period and writes down any excess and obsolete inventory to its estimated net realizable value in the period it is identified. If they occur, such impairment charges are recorded as a component of cost of goods sold in the consolidated statements of operations and comprehensive loss. Inventory on-hand that will be sold beyond the Company's normal operating cycle is classified as non-current and grouped with other assets on the Company's consolidated balance sheets. At June 30, 2019, the Company did not have any such inventory. Prior to the initial date regulatory approval is received, costs related to the production of inventory are recorded as research and development expense on the Company’s consolidated statements of operations and comprehensive loss in the period incurred. The Company received FDA approval for ZULRESSO on March 19, 2019 and subsequently began capitalizing costs related to inventory manufacturing.
Cost of Goods Sold	Cost of Goods Sold Cost of goods sold includes direct and indirect costs related to the manufacturing and distribution of ZULRESSO, including third-party manufacturing costs, packaging services, freight, third-party royalties payable on the Company’s net product revenues and amortization of intangible assets associated with ZULRESSO. Cost of goods sold may also include period costs related to certain inventory manufacturing services, inventory adjustment charges, as well as manufacturing variances. In connection with the FDA approval of ZULRESSO on March 19, 2019, the Company subsequently began capitalizing inventory manufactured or purchased after this date. As a result, certain manufacturing costs associated with product shipments of ZULRESSO were expensed prior to FDA approval and, therefore, are not included in cost of goods sold during the current period.
Accounts Receivable	Accounts Receivable The Company’s trade accounts receivable consist of amounts due from specialty distributors and specialty pharmacies in the U.S. related to sales of ZULRESSO and have standard payment terms that generally require payment within 30 to 60 days from the invoice date. The Company monitors the financial performance and creditworthiness of customers so that it can properly assess and respond to changes in their credit profile. The Company reserves against trade accounts receivable for estimated losses that may arise from a customer’s inability to pay and any amounts determined to be uncollectible are written off against the reserve when it is probable that the receivable will not be collected. Trade accounts receivable are included in prepaid expenses and other current assets on the consolidated balance sheets and the amount was not significant as of June 30, 2019.
Intangible Assets	Intangible assets The Company had no intangible assets as of December 31, 2018. As a result of the approval by the FDA of the New Drug Application for ZULRESSO in March 2019, the Company was required to pay to CyDex Pharmaceuticals, Inc. (“CyDex”) During the three months ended June 30, 2019, the Company began to amortize the asset and record the expense to cost of goods sold.
Leases	Leases The Company determines if an arrangement is a lease at contract inception. Operating lease assets represent the Company’s right to use an underlying asset for the lease term and operating lease liabilities represent the Company’s obligation to make lease payments arising from the lease. Operating lease assets and liabilities are recognized at the commencement date of the lease based upon the present value of lease payments over the lease term. When determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. The Company uses the implicit interest rate when readily determinable and uses the Company’s incremental borrowing rate when the implicit rate is not readily determinable based upon the information available at the commencement date in determining the present value of the lease payments. The lease payments used to determine the Company’s operating lease assets may include lease incentives, stated rent increases and escalation clauses linked to rates of inflation when determinable and are recognized in the Company’s operating lease assets in the Company’s condensed consolidated balance sheets. In addition, the Company’s contracts contain lease and non-lease components. The Company combines lease and non-lease components, which are accounted for together as lease components. The Company’s operating leases are reflected in right of use operating asset, other current liabilities and long-term lease operating liability, net of current portion in the Company’s condensed consolidated balance sheets. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. Short-term leases, defined as leases that have a lease term of 12 months or less at the commencement date, are excluded from this treatment and are recognized on a straight-line basis over the term of the lease.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-02, Leases Leases (Topic 842): Targeted Improvements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which introduces a new methodology for accounting for credit losses on financial instruments, including available-for-sale debt securities. The guidance establishes a new "expected loss model" that requires entities to estimate current expected credit losses on financial instruments by using all practical and relevant information. Any expected credit losses are to be reflected as allowances rather than reductions in the amortized cost of available-for-sale debt securities. Early adoption is permitted for annual periods beginning after December 15, 2018, and interim periods therein. The Company adopted the standard on the required effective date of January 1, 2019. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures . In June 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718) – Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”), which aligns the accounting for share-based payment awards issued to employees and non-employees. Under the new guidance, the existing guidance regarding employees will apply to share-based transactions with non-employees, as long as the transaction is not effectively a form of financing, with the exception of specific guidance related to the attribution of compensation cost. The cost of non-employee awards will continue to be recorded as if the grantor had paid cash for the goods or services. In addition, the contractual term will be able to be used in lieu of an expected term in the option-pricing model for non-employee awards. The Company adopted the standard on the required effective date of January 1, 2019. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s consolidated financial statements upon adoption.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Summary of Company's Money Market Funds and Marketable Securities	The following tables summarize the Company’s money market funds and marketable securities as of June 30, 2019 and December 31, 2018. June 30, 2019 Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in thousands) Cash equivalents: Cash equivalents $ 166,185 $ 166,185 $ — $ — Total cash equivalents 166,185 166,185 — — Marketable securities: U.S. government securities 290,571 — 290,571 — U.S. corporate bonds 478,806 — 478,806 — International corporate bonds 147,470 — 147,470 — U.S. commercial paper 107,099 — 107,099 — International commercial paper 46,418 — 46,418 — Total marketable securities 1,070,364 — 1,070,364 — $ 1,236,549 $ 166,185 $ 1,070,364 $ — December 31, 2018 Total Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in thousands) Cash equivalents: Cash equivalents $ 190,943 $ 190,943 $ — $ — Total cash equivalents 190,943 190,943 — — Marketable securities: U.S. government securities 220,482 — 220,482 — U.S. corporate bonds 258,566 — 258,566 — International corporate bonds 78,468 — 78,468 — U.S. commercial paper 77,611 — 77,611 — International commercial paper 96,706 — 96,706 — Total marketable securities 731,833 — 731,833 — $ 922,776 $ 190,943 $ 731,833 $ —
Summary of Gross Unrealized Gains and Losses of Marketable Securities	The following tables summarize the gross unrealized gains and losses of the Company’s marketable securities as of June 30, 2019 and December 31, 2018: June 30, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Assets: U.S. government securities $ 290,271 $ 302 $ (2 ) $ 290,571 U.S. corporate bonds 477,932 942 (68 ) 478,806 International corporate bonds 147,062 434 (26 ) 147,470 U.S. commercial paper 107,105 1 (7 ) 107,099 International commercial paper 46,419 — (1 ) 46,418 $ 1,068,789 $ 1,679 $ (104 ) $ 1,070,364 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Assets: U.S. government securities $ 220,531 $ 8 $ (57 ) $ 220,482 U.S. corporate bonds 258,876 6 (316 ) 258,566 International corporate bonds 78,600 — (132 ) 78,468 U.S. commercial paper 77,630 8 (27 ) 77,611 International commercial paper 96,711 8 (13 ) 96,706 $ 732,348 $ 30 $ (545 ) $ 731,833

Balance Sheet Components (Table

Balance Sheet Components (Tables)	6 Months Ended
	Jun. 30, 2019
Balance Sheet Related Disclosures [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net, consists of the following: June 30, December 31, 2019 2018 (in thousands) Computer hardware and software $ 2,427 $ 2,148 Furniture and equipment 1,774 1,002 Leasehold improvements 7,298 4,709 11,499 7,859 Less: Accumulated depreciation (3,136 ) (2,216 ) $ 8,363 $ 5,643
Summary of Accrued Expenses	Accrued expenses consist of the following: June 30, December 31, 2019 2018 (in thousands) Development costs $ 28,498 $ 21,216 Employee-related expenses 15,585 19,638 Professional services 14,299 10,903 Other accrued expenses 530 237 $ 58,912 $ 51,994

Leases, Commitments and Conti_2

Leases, Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Schedule of Condensed Consolidated Balance Sheets of Operating Leases	The following table summarizes the presentation in the Company’s condensed consolidated balance sheets of operating leases: (In thousands) Balance sheet location As of June 30, 2019 Assets Right of use operating asset Right of use operating asset $ 37,224 Liabilities Current operating lease liabilities Other current liabilities 7,393 Long-term operating lease liabilities Long-term lease operating liability, net of current portion 33,309 Total operating lease liabilities $ 40,702
Schedule of Effect of Lease Cost In Condensed Consolidated Statements of Operations and Comprehensive Loss	The following table summarizes the effect of lease costs in the Company’s condensed consolidated statements of operations and comprehensive loss: Three Months Ended Six Months Ended (In thousands) June 30, 2019 June 30, 2019 Operating lease cost $ 2,436 $ 4,880
Schedule of Minimum Lease Payments	The minimum lease payments are expected to be as follows: Years Ending December 31, (in thousands) 2019 (remaining six months) $ 5,080 2020 10,244 2021 9,972 2022 8,898 2023 9,105 Thereafter 5,560 Total lease payments 48,859 Less imputed interest (8,157 ) Present value of operating lease liabilities $ 40,702
Schedule of Future Minimum Lease Payments, Under Non-Cancelable Operating Leases	Under the prior lease guidance, future minimum lease payments under non-cancelable operating leases were as follows at December 31, 2018: Years Ending December 31, (in thousands) 2019 $ 7,918 2020 8,299 2021 8,463 2022 8,692 2023 8,894 Thereafter 5,415 $ 47,681
Schedule of Weighted Average Remaining Lease Term and Weighted Average Discount Rate of Our Operating Leases	The weighted average remaining lease term and weighted average discount rate of the Company’s operating leases are as follows: As of June 30, 2019 Weighted average remaining lease term in years 4.86 Weighted average discount rate 7.5%
Schedule of Supplemental Disclosure of Cash Flow Information Related To Operating Leases	Supplemental disclosure of cash flow information related to the Company’s operating leases included in cash flows used by operating activities in the condensed consolidated statements of cash flows is as follows: Three Months Ended Six Months Ended (In thousands) June 30, 2019 June 30, 2019 Cash paid for amounts included in the measurement of lease liabilities $ 2,513 $ 4,867 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ 872 $ 872

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Activity Relating to Restricted Stock Units	The table below summarizes activity relating to restricted stock units: Shares Outstanding as of December 31, 2018 82,700 Granted 370,456 Vested (13,250 ) Forfeited (43,240 ) Outstanding as of June 30, 2019 396,666
Summary of Stock-Based Compensation Expense for Stock Options, Restricted Stock Units and Employee Stock Purchase Plan Recognized	Stock-based compensation expense for stock options, restricted stock units and the employee stock purchase plan recognized during the three and six months ended June 30, 2019 and 2018 was as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (in thousands) Research and development $ 13,672 $ 12,095 $ 34,417 $ 20,994 Selling, general and administrative 21,095 16,933 44,466 23,851 $ 34,767 $ 29,028 $ 78,883 $ 44,845
Summary of Stock-Based Compensation Expense by Award Type Recognized	Stock-based compensation expense by award type recognized during the three and six months ended June 30, 2019 and 2018 was as follows: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 (in thousands) Stock options $ 34,280 $ 28,627 $ 77,844 $ 44,007 Restricted stock units — 155 58 324 Employee stock purchase plan 487 246 981 514 $ 34,767 $ 29,028 $ 78,883 $ 44,845
Summary of Activity Relating to Stock Options	The table below summarizes activity related to stock options: Shares Weighted Average Exercise Price Weighted Average Remaining Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2018 7,530,767 $ 93.22 8.03 $ 227,447 Granted 1,355,931 — Exercised (745,558 ) — Forfeited (281,850 ) — Outstanding as of June 30, 2019 7,859,290 $ 107.81 7.98 $ 600,965 Exercisable as of June 30, 2019 3,321,049 $ 70.02 6.89 $ 378,713

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Summary of Basic and Diluted Net Loss Per Share	Basic and diluted net loss per share was calculated as follows for the three and six months ended June 30, 2019 and 2018: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Basic net loss per share: Numerator: Net loss (in thousands) $ (168,221 ) $ (16,978 ) $ (331,627 ) $ (91,576 ) Denominator: Weighted average common stock outstanding - basic 51,257,640 46,541,716 49,882,377 45,439,666 Dilutive effect of shares of common stock equivalents resulting from common stock options and restricted stock units — — — — Weighted average common stock outstanding - diluted 51,257,640 46,541,716 49,882,377 45,439,666 Net loss per share—basic and diluted $ (3.28 ) $ (0.36 ) $ (6.65 ) $ (2.02 )
Summary of Anti-Dilutive Common Stock Equivalents Outstanding	The following common stock equivalents outstanding as of June 30, 2019 and 2018 were excluded from the calculation of diluted net loss per share for the periods presented because including them would have been anti-dilutive: Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Stock options 7,362,768 6,207,172 7,362,768 6,207,172 Restricted stock units — 13,950 — 13,950 Employee stock purchase plan 39,006 8,004 39,006 8,004 7,401,774 6,229,126 7,401,774 6,229,126

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) - USD ($) $ in Thousands	111 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Nature Of Business [Line Items]
Accumulated deficit	$ (1,294,956)	$ (963,329)
Redeemable Convertible Preferred Stock [Member] | Convertible Notes [Member] | Initial Public Offering [Member]
Nature Of Business [Line Items]
Net proceeds from sale of equity and notes	$ 2,200,000

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Mar. 31, 2019	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Intangible assets				$ 0
Amortization of intangible assets	$ 0
Operating lease liabilities		$ 40,702,000	$ 44,200,000
Operating lease right-of-use asset		$ 37,224,000	$ 41,100,000
CyDex License Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Milestone payments	3,000,000
The Regents of University of California [Member]
Summary Of Significant Accounting Policies [Line Items]
Milestone payments	$ 500,000
Product Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Incremental costs incurred expected amortization period of asset		true

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Company's Money Market Funds and Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	$ 166,185	$ 190,943
Total marketable securities	1,070,364	731,833
Total cash equivalents and marketable securities	1,236,549	922,776
Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	166,185	190,943
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	166,185	190,943
Total cash equivalents and marketable securities	166,185	190,943
Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	166,185	190,943
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	1,070,364	731,833
Total cash equivalents and marketable securities	1,070,364	731,833
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	290,571	220,482
U.S. Government Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	290,571	220,482
U.S. Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	478,806	258,566
U.S. Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	478,806	258,566
International Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	147,470	78,468
International Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	147,470	78,468
U.S. Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	107,099	77,611
U.S. Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	107,099	77,611
International Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	46,418	96,706
International Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	$ 46,418	$ 96,706

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2019USD ($)MarketableSecurity	Dec. 31, 2018USD ($)MarketableSecurity	Jun. 30, 2018USD ($)
Debt Instrument Fair Value Carrying Value [Line Items]
Transfers among the Level 1, Level 2 and Level 3 categories	$ 0		$ 0
Number of marketable securities not part of remaining contractual maturities of one year or less | MarketableSecurity	48
Marketable securities fair value held to maturity	$ 185,000,000
Impairment of assets	$ 0	$ 0
U.S. Corporate Bonds [Member]
Debt Instrument Fair Value Carrying Value [Line Items]
Number of marketable securities not part of remaining contractual maturities of one year or less | MarketableSecurity		2
Maximum [Member]
Debt Instrument Fair Value Carrying Value [Line Items]
Marketable securities, remaining contractual maturities	1 year	1 year
Marketable securities held, matuirity period	2 years
Minimum [Member]
Debt Instrument Fair Value Carrying Value [Line Items]
Marketable securities held, matuirity period	1 year

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Gross Unrealized Gains and Losses of Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,068,789	$ 732,348
Gross Unrealized Gains	1,679	30
Gross Unrealized Losses	(104)	(545)
Fair Value	1,070,364	731,833
U.S. Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	290,271	220,531
Gross Unrealized Gains	302	8
Gross Unrealized Losses	(2)	(57)
Fair Value	290,571	220,482
U.S. Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	477,932	258,876
Gross Unrealized Gains	942	6
Gross Unrealized Losses	(68)	(316)
Fair Value	478,806	258,566
International Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	147,062	78,600
Gross Unrealized Gains	434
Gross Unrealized Losses	(26)	(132)
Fair Value	147,470	78,468
U.S. Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	107,105	77,630
Gross Unrealized Gains	1	8
Gross Unrealized Losses	(7)	(27)
Fair Value	107,099	77,611
International Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	46,419	96,711
Gross Unrealized Gains		8
Gross Unrealized Losses	(1)	(13)
Fair Value	$ 46,418	$ 96,706

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 11,499	$ 7,859
Less: Accumulated depreciation	(3,136)	(2,216)
Property and equipment, net	8,363	5,643
Computer Hardware and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,427	2,148
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,774	1,002
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 7,298	$ 4,709

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 500	$ 200	$ 920	$ 493
Computer Hardware and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			3 years
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life			5 years

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Development costs	$ 28,498	$ 21,216
Employee-related expenses	15,585	19,638
Professional services	14,299	10,903
Other accrued expenses	530	237
Total accrued expenses	$ 58,912	$ 51,994

Leases, Commitments and Conti_3

Leases, Commitments and Contingencies - Operating Leases - Additional Information (Detail) $ in Millions

Jun. 30, 2019ft²

Feb. 28, 2019ft²

Oct. 02, 2018ft²

Sep. 30, 2018ft²

Aug. 01, 2018ft²

Mar. 31, 2019ft²

Dec. 31, 2018ft²

Oct. 31, 2018ft²

May 31, 2018ft²

Apr. 30, 2018ft²

Jun. 30, 2019USD ($)

Mar. 31, 2018ft²

Jun. 30, 2019USD ($)

Commitments And Contingencies [Line Items]

Operating lease option to extend

true

Operating lease renewal term

5 years

5 years

5 years

Expenses for short term lease | $

$ 0.1

$ 0.3

Operating Lease One [Member]

Commitments And Contingencies [Line Items]

Office space rent under operating lease

63,017

58,442

54,943

63,017

58,442

Lease expire date

Aug. 31, 2024

Aug. 31, 2024

Aug. 31, 2024

Increased office space rent

4,575

3,499

Operating Lease Two [Member]

Commitments And Contingencies [Line Items]

Office space rent under operating lease

40,419

19,805

Lease expire date

Aug. 31, 2024

Feb. 28, 2022

Aug. 31, 2024

Increased office space rent

7,133

13,481

20,614

Operating Lease Three [Member]

Commitments And Contingencies [Line Items]

Office space rent under operating lease

15,525

Lease expire date

Nov. 30, 2024

Operating Lease Five [Member]

Commitments And Contingencies [Line Items]

Office space rent under operating lease

15,975

Lease expire date

Feb. 28, 2024

Minimum [Member]

Commitments And Contingencies [Line Items]

Operating lease remaining lease terms

1 year

Maximum [Member]

Commitments And Contingencies [Line Items]

Operating lease remaining lease terms

6 years

Leases, Commitments and Conti_4

Leases, Commitments and Contingencies - Schedule of Condensed Consolidated Balance Sheets of Operating Leases (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019
Assets
Right of use operating asset	$ 37,224	$ 41,100
Liabilities
Current operating lease liabilities	7,393
Long-term operating lease liabilities	33,309
Total operating lease liabilities	$ 40,702	$ 44,200

Leases, Commitments and Conti_5

Leases, Commitments and Contingencies - Schedule of Effect of Lease Cost In Condensed Consolidated Statements of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Operating lease cost	$ 2,436	$ 4,880

Leases, Commitments and Conti_6

Leases, Commitments and Contingencies - Schedule of Minimum Lease Payments (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Jan. 01, 2019
Lessee Lease Description [Line Items]
Operating lease liabilities	$ 40,702	$ 44,200
ASU Topic (842) [Member]
Lessee Lease Description [Line Items]
2019 (remaining six months)	5,080
2020	10,244
2021	9,972
2022	8,898
2023	9,105
Thereafter	5,560
Total lease payments	48,859
Less imputed interest	(8,157)
Operating lease liabilities	$ 40,702

Leases, Commitments and Conti_7

Leases, Commitments and Contingencies - Schedule of Future Minimum Lease Payments, Under Non-Cancelable Operating Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 7,918
2020	8,299
2021	8,463
2022	8,692
2023	8,894
Thereafter	5,415
Total Operating leases, future minimum payments	$ 47,681

Leases, Commitments and Conti_8

Leases, Commitments and Contingencies - Schedule of Weighted Average Remaining Lease Term and Weighted Average Discount Rate of Our Operating Leases (Detail)	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Weighted average remaining lease term in years	4 years 10 months 9 days
Weighted average discount rate	7.50%

Leases, Commitments and Conti_9

Leases, Commitments and Contingencies - Schedule of Supplemental Disclosure of Cash Flow Information Related To Operating Leases (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	$ 2,513	$ 4,867
Right-of-use assets obtained in exchange for lease obligations - Operating leases	$ 872	$ 872

Leases, Commitments and Cont_10

Leases, Commitments and Contingencies - CyDex License Agreement - Additional Information (Detail) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Commitments And Contingencies [Line Items]
Research and development expense	$ 89,059,000		$ 68,980,000	$ 175,457,000	$ 118,250,000
CyDex License Agreement [Member]
Commitments And Contingencies [Line Items]
Research and development expense				1,000,000
Milestone payments		$ 3,000,000
CyDex License Agreement [Member] | First and Second Clinical Development Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	800,000			800,000
CyDex License Agreement [Member] | First and Second Regulatory Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	3,800,000			3,800,000
CyDex License Agreement [Member] | Third and Fourth Clinical Development Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	1,300,000			1,300,000
CyDex License Agreement [Member] | Third and Fourth Regulatory Milestones [Member] | Brexanolone [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	8,500,000			8,500,000
CyDex License Agreement [Member] | Clinical Development [Member] | Brexanolone [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense	0
Milestone payments	0
Milestone payments related to intangible assets	0
CyDex License Agreement [Member] | Clinical Development [Member] | SAGE-689 [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	800,000			800,000
CyDex License Agreement [Member] | Regulatory Milestones [Member] | Brexanolone [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense	0		800,000		800,000
Milestone payments	0		$ 800,000		$ 800,000
Intangible asset related to milestone	3,000,000			3,000,000
Milestone payments related to intangible assets	0			3,000,000
CyDex License Agreement [Member] | Regulatory Milestones [Member] | SAGE-689 [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	1,800,000			1,800,000
CyDex License Agreement [Member] | Clinical Development and Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense				2,300,000
Milestone payments				2,300,000
Intangible asset related to milestone	$ 3,000,000			3,000,000
Milestone payments related to intangible assets				$ 3,000,000

Leases, Commitments and Cont_11

Leases, Commitments and Contingencies - University of California License Agreements - Additional Information (Detail) - University of California License Agreements [Member] - USD ($)	Dec. 31, 2015	Jun. 30, 2015	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2015
Commitments And Contingencies [Line Items]
Upfront payment		$ 50,000
Annual license maintenance fee							$ 15,000
Research and development expense related to milestone expense			$ 0	$ 200,000		$ 200,000
Milestone payments			0	$ 200,000		$ 200,000
After The Effective Date [Member]
Commitments And Contingencies [Line Items]
Licenses Expiration period, maximum	27 years
After The First Sale [Member]
Commitments And Contingencies [Line Items]
Licenses Expiration period, maximum	15 years
Clinical Development [Member]
Commitments And Contingencies [Line Items]
Milestone payments	$ 100,000
Clinical Development [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Percentage of net sales paid as royalties	1.00%
Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Intangible asset related to milestone			500,000		$ 500,000
Milestone payments related to intangible assets					500,000
Regulatory Milestones [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments		700,000
Sales Milestones [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments		$ 2,000,000
Regulatory and Sales Milestones [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense					300,000
Milestone payments					300,000
Intangible asset related to milestone			$ 500,000		500,000
Milestone payments related to intangible assets					$ 500,000

Leases, Commitments and Cont_12

Leases, Commitments and Contingencies - Washington University License Agreement - Additional Information (Detail) - Washington University License Agreement [Member] - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Nov. 30, 2013	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2013
Commitments And Contingencies [Line Items]
Upfront non-refundable payment	$ 50,000
Annual license maintenance fee						$ 15,000
Issuance of common stock, shares						47,619
Research and development expense related to issue of common stock obligation						$ 100,000
Research and development expense related to milestone expense		$ 0	$ 0	$ 0	$ 0
Milestone payments		$ 0	$ 0	0	$ 0
Clinical Development [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense				50,000
Milestone payments				$ 50,000
Maximum [Member] | Clinical Development [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	700,000
Maximum [Member] | Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 500,000

Leases, Commitments and Cont_13

Leases, Commitments and Contingencies - Consulting Agreement - Additional Information (Detail) - Consulting Agreement [Member] - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2014	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense		$ 0	$ 0	$ 0	$ 0
Milestone payments		$ 0	$ 0	0	$ 0
Clinical Development and Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Shares of common stock for attaining milestones	126,984
Research and development expense related to milestone expense				1,800,000
Milestone payments				500,000
Payments for stock issued upon reaching a milestone				$ 1,300,000
Milestone based share compensation, shares issued				39,681
Clinical Development and Regulatory Milestones [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments	$ 2,000,000

Collaboration Agreement - Addit

Collaboration Agreement - Additional Information (Detail) - USD ($)	Jun. 12, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue		$ 873,000	$ 90,000,000	$ 1,338,000	$ 90,000,000
Shionogi Collaboration Agreement [Member] | SAGE-217 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement effective date	Jun. 12, 2018
Upfront payment	$ 90,000,000
Average percentage on tiered royalties	20.00%
Standalone selling price of license performance obligation		$ 90,000,000		90,000,000
Revenue				$ 90,000,000
Shionogi Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payment receivable	$ 485,000,000
Shionogi Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member] | Regulatory Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments	70,000,000
Shionogi Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member] | Commercial Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments	30,000,000
Shionogi Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member] | Sales Milestones [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future milestone payments	$ 385,000,000

Sale of Equity Securities - Add

Sale of Equity Securities - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Feb. 27, 2019	Feb. 13, 2018
Equity [Abstract]
Issuance of common stock, shares	3,833,334	4,032,012
Common stock price per share	$ 150	$ 164
Proceeds from public offering of common stock, net of commissions and underwriting discounts and offering costs	$ 560.9	$ 631.2

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail)	Jan. 01, 2019shares	Jun. 30, 2019USD ($)shares	Mar. 31, 2019USD ($)Milestone	Jun. 30, 2018USD ($)shares	Mar. 31, 2018shares	Mar. 31, 2017shares	Jun. 30, 2019USD ($)$ / sharesshares	Jun. 30, 2018USD ($)$ / sharesshares	Dec. 31, 2018shares	Dec. 31, 2017	Sep. 20, 2018shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of options outstanding		11,045,846					11,045,846
Common stock available for issuance under stock option plan		2,781,281					2,781,281
Stock-based compensation expense | $		$ 34,767,000		$ 29,028,000			$ 78,883,000	$ 44,845,000
Weighted average grant date fair value per share | $ / shares							$ 99.11	$ 114.72
2011 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted							0
2014 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares annual increase added to plan	1,875,530
2014 Stock Option Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of increase on outstanding shares of Common stock									4.00%
2016 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares reserved for issuance											1,200,000
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted						32,500	370,456
Share based compensation granted under plan vest period						2 years
Fair value of restricted stock units vested | $		$ 0		0			$ 2,000,000	$ 2,600,000
Stock-based compensation expense | $				$ 155,000			$ 58,000	$ 324,000
Restricted Stock Units [Member] | Restricted Stock Units Vest One Year Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units cliff vesting percentage						50.00%
Restricted stock units vesting period month and year						2018-02
Restricted Stock Units [Member] | Restricted Stock Units Vest Two Year Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units cliff vesting percentage						50.00%
Restricted stock units vesting period month and year						2019-02
Performance Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted		16,345			33,600		370,456
Performance Restricted Stock Units [Member] | Commercial Milestones [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted				37,800
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted				200,250			0	524,003
Total unrecognized stock-based compensation expense | $		$ 35,200,000					$ 35,200,000
Number of shares outstanding and unvested stock options		505,131					505,131
Performance-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Milestones not achieved | Milestone			1
Stock-based compensation expense | $		$ 0	$ 14,200,000					$ 0
Percentage of performance based grants that were achieved									20.00%	33.00%
Performance-Based Stock Options [Member] | Consultant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $				$ 6,900,000
Commercial Milestones [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense | $		$ 2,100,000					$ 16,300,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted							1,355,931
Total number of options outstanding		7,859,290					7,859,290		7,530,767
Stock-based compensation expense | $		$ 34,280,000		$ 28,627,000			$ 77,844,000	44,007,000
Total unrecognized stock-based compensation expense | $		$ 310,700,000					$ 310,700,000
Weighted average period of unrecognized compensation costs							2 years 8 months 26 days
Intrinsic value of options exercised | $							$ 87,400,000	$ 64,400,000

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Activity Relating to Restricted Stock Units (Detail) - Restricted Stock Units [Member] - shares	3 Months Ended	6 Months Ended
	Mar. 31, 2017	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, Shares at beginning balance		82,700
Granted, Shares	32,500	370,456
Vested, Shares		(13,250)
Forfeited, Shares		(43,240)
Outstanding, Shares at ending balance		396,666

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock-Based Compensation Expense for Stock Options, Restricted Stock Units and Employee Stock Purchase Plan Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 34,767	$ 29,028	$ 78,883	$ 44,845
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	13,672	12,095	34,417	20,994
Selling, General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 21,095	$ 16,933	$ 44,466	$ 23,851

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock-Based Compensation Expense by Award Type Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 34,767	$ 29,028	$ 78,883	$ 44,845
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	34,280	28,627	77,844	44,007
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense		155	58	324
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 487	$ 246	$ 981	$ 514

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of Activity Relating to Stock Options (Detail) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, Outstanding Shares	11,045,846
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Outstanding Shares	7,530,767
Granted, Shares	1,355,931
Exercised, Shares	(745,558)
Forfeited, Shares	(281,850)
Ending balance, Outstanding Shares	7,859,290	7,530,767
Exercisable, Shares	3,321,049
Beginning balance, Outstanding Weighted Average Exercise Price | $ / shares	$ 93.22
Ending balance, Outstanding Weighted Average Exercise Price | $ / shares	107.81	$ 93.22
Exercisable, Weighted Average Exercise Price | $ / shares	$ 70.02
Outstanding, Weighted Average Remaining Life	7 years 11 months 23 days	8 years 10 days
Exercisable, Weighted Average Remaining Life	6 years 10 months 20 days
Outstanding, Aggregate Intrinsic Value | $	$ 600,965	$ 227,447
Exercisable, Aggregate Intrinsic Value | $	$ 378,713

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ 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
Numerator:
Net loss	$ (168,221)	$ (163,406)	$ (16,978)	$ (74,598)	$ (331,627)	$ (91,576)
Denominator:
Weighted average common stock outstanding - basic	51,257,640		46,541,716		49,882,377	45,439,666
Dilutive effect of shares of common stock equivalents resulting from common stock options and restricted stock units	0		0		0	0
Weighted average common stock outstanding - diluted	51,257,640		46,541,716		49,882,377	45,439,666
Net loss per share—basic and diluted	$ (3.28)		$ (0.36)		$ (6.65)	$ (2.02)

Net Loss Per Share - Summary _2

Net Loss Per Share - Summary of Anti-Dilutive Common Stock Equivalents Outstanding (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	7,401,774	6,229,126	7,401,774	6,229,126
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	7,362,768	6,207,172	7,362,768	6,207,172
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents		13,950		13,950
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	39,006	8,004	39,006	8,004