Sage Therapeutics (SAGE) 10-K 24 Feb 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 17, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	SAGE
Entity Registrant Name	Sage Therapeutics, Inc.
Entity Central Index Key	0001597553
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	true
Entity Common Stock, Shares Outstanding		58,381,933
Entity Public Float			$ 2,120,561,372
Entity Interactive Data Current	Yes
Title of 12(b) Security	common stock, $0.0001 par value per share
Security Exchange Name	NASDAQ
Entity File Number	001-36544
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-4486580
Entity Address, Address Line One	215 First Street
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	299-8380
Document Annual Report	true
Document Transition Report	false
Documents Incorporated by Reference	Part III of this Annual Report on Form 10-K incorporates by reference certain information from the registrant’s definitive Proxy Statement for its 2021 annual meeting of shareholders, which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year end of December 31, 2020. Except with respect to information specifically incorporated by reference in this Form 10-K, the Proxy Statement is not deemed to be filed as part of this Form 10-K.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 1,661,082	$ 126,705
Marketable securities	438,467	881,688
Prepaid expenses and other current assets	22,821	26,700
Total current assets	2,122,370	1,035,093
Property and equipment, net	6,755	9,126
Restricted cash	1,716	2,367
Right-of-use operating asset	25,064	33,771
Other long-term assets	3,341	3,793
Total assets	2,159,246	1,084,150
Current liabilities:
Accounts payable	3,691	15,266
Accrued expenses	54,851	86,618
Operating lease liability, current portion	8,662	10,244
Total current liabilities	67,204	112,128
Operating lease liability, net of current portion	19,438	26,848
Other liabilities	270	519
Total liabilities	86,912	139,495
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at December 31, 2020 and December 31, 2019; no shares issued or outstanding at December 31, 2020 and December 31, 2019
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at December 31, 2020 and December 31, 2019; 58,311,444 and 51,880,227 shares issued at December 31, 2020 and December 31, 2019; 58,308,411 and 51,877,194 shares outstanding at December 31, 2020 and December 31, 2019	6	5
Treasury stock, at cost, 3,033 shares at December 31, 2020 and December 31, 2019	(400)	(400)
Additional paid-in capital	3,109,807	2,587,322
Accumulated deficit	(1,037,494)	(1,643,567)
Accumulated other comprehensive gain	415	1,295
Total stockholders’ equity	2,072,334	944,655
Total liabilities and stockholders’ equity	$ 2,159,246	$ 1,084,150

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
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	58,311,444	51,880,227
Common stock, shares outstanding	58,308,411	51,877,194
Treasury stock, shares	3,033	3,033

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Total revenue	$ 1,114,200	$ 6,868	$ 90,273
Type of Revenue [Extensible List]		us-gaap:CollaborativeArrangementMember	us-gaap:CollaborativeArrangementMember
Operating costs and expenses:
Cost of goods sold	565	$ 400
Research and development	292,714	368,815	$ 282,107
Selling, general and administrative	196,952	345,777	201,404
Restructuring	27,743
Total operating costs and expenses	517,974	714,992	483,511
Income (loss) from operations	596,226	(708,124)	(393,238)
Interest income, net	9,597	27,804	20,334
Other income, net	250	82	22
Net income (loss)	$ 606,073	$ (680,238)	$ (372,882)
Net income (loss) per share—basic	$ 11.66	$ (13.38)	$ (8.08)
Net income (loss) per share—diluted	$ 11.43	$ (13.38)	$ (8.08)
Weighted average number of common shares outstanding—basic	51,983,188	50,833,837	46,121,194
Weighted average number of common shares outstanding—diluted	53,003,115	50,833,837	46,121,194
Comprehensive income (loss):
Net income (loss)	$ 606,073	$ (680,238)	$ (372,882)
Other comprehensive items:
Unrealized gain (loss) on marketable securities	(880)	1,810	(486)
Total other comprehensive gain (loss)	(880)	1,810	(486)
Total comprehensive income (loss)	605,193	(678,428)	(373,368)
Product Revenue [Member]
Total revenue	6,700	3,957
Collaboration Revenue [Member]
Total revenue	$ 1,107,500	$ 2,911	$ 90,273

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	27,014			27,014
Issuance of common stock from exercise of stock options, Shares		824,188
Issuance of common stock under the employee stock purchase plan	2,705			2,705
Issuance of common stock under the employee stock purchase plan, Shares		19,687
Purchase of treasury stock, Amount	(98)		$ (98)
Purchase of treasury stock, Shares			2,073
Stock-based compensation expense	100,993			100,993
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 gain (loss) on available-for-sale securities	(486)				(486)
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 income (loss)	(372,882)					(372,882)
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	44,276			44,276
Issuance of common stock from exercise of stock options, Shares		1,031,989
Issuance of common stock under the employee stock purchase plan	5,744			5,744
Issuance of common stock under the employee stock purchase plan, Shares		55,404
Purchase of treasury stock, Amount	(189)		$ (189)
Stock-based compensation expense	151,508			151,508
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 gain (loss) on available-for-sale securities	1,810				1,810
Vesting of restricted stock units, net of employee tax obligations	(2,175)			(2,175)
Vesting of restricted stock units, net of employee tax obligations, Shares		68,204
Net income (loss)	(680,238)					(680,238)
Balances at Dec. 31, 2019	944,655	$ 5	$ (400)	2,587,322	1,295	(1,643,567)
Balances, Shares at Dec. 31, 2019		51,877,194	3,033
Issuance of common stock from exercise of stock options, Amount	5,082			5,082
Issuance of common stock from exercise of stock options, Shares		117,025
Issuance of common stock under the employee stock purchase plan	4,936			4,936
Issuance of common stock under the employee stock purchase plan, Shares		72,719
Issuance of common stock under the Stock Purchase Agreement	$ 417,500	$ 1		417,499
Issuance of common stock under the Stock Purchase Agreement, Shares		6,241,473
Purchase of treasury stock, Shares	(3,033)
Stock-based compensation expense	$ 94,968			94,968
Unrealized gain (loss) on available-for-sale securities	(880)				(880)
Net income (loss)	606,073					606,073
Balances at Dec. 31, 2020	$ 2,072,334	$ 6	$ (400)	$ 3,109,807	$ 415	$ (1,037,494)
Balances, Shares at Dec. 31, 2020		58,308,411	3,033

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net income (loss)	$ 606,073	$ (680,238)	$ (372,882)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Stock-based compensation expense	95,994	153,231	101,963
Premium on marketable securities	(1,736)	(3,674)	(215)
Amortization of premium (discount) on marketable securities	1,048	(6,966)	(9,892)
Depreciation	2,630	2,283	1,143
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	3,879	(4,781)	(15,462)
Other long-term assets	452	(3,793)
Right-of-use operating asset	6,397	8,168
Operating lease liabilities, current	36	2,804
Operating lease liabilities, non-current	(6,825)	(10,761)
Accounts payable	(11,511)	(18,783)	24,544
Accrued expenses and other liabilities	(32,157)	33,804	10,130
Net cash provided by (used in) operating activities	664,280	(528,706)	(260,671)
Cash flows from investing activities
Proceeds from sales and maturities of marketable securities	901,749	1,171,270	974,757
Purchases of marketable securities	(458,720)	(1,308,675)	(1,484,358)
Purchases of property and equipment	(345)	(5,751)	(2,860)
Net cash provided by (used in) investing activities	442,684	(143,156)	(512,461)
Cash flows from financing activities
Proceeds from stock option exercises and employee stock purchase plan issuances	9,262	48,850	29,108
Payment of employee tax obligations related to vesting of restricted stock units		(2,175)	(904)
Payments of offering costs		(328)	(340)
Proceeds from the sale of common stock under the Stock Purchase Agreement	417,500
Proceeds from public offerings of common stock, net of commissions and underwriting discounts		561,277	631,494
Net cash provided by financing activities	426,762	607,624	659,358
Net increase (decrease) in cash, cash equivalents and restricted cash	1,533,726	(64,238)	(113,774)
Cash, cash equivalents and restricted cash at beginning of period	129,072	193,310	307,084
Cash, cash equivalents and restricted cash at end of period	1,662,798	129,072	193,310
Supplemental disclosure of non-cash operating and investing activities
Purchases of property and equipment included in accounts payable		65	51
Right-of-use assets obtained in exchange for new operating lease liabilities		$ 872
Lease asset de-recognized upon lease cancellation	$ 2,310
Landlord tenant incentive included in other current assets			$ 229

Nature of the Business

Nature of the Business	12 Months Ended
	Dec. 31, 2020
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 first product, ZULRESSO® (brexanolone) CIV injection, is approved in the U.S. as a treatment for postpartum depression (“PPD”) in adults. The Company launched ZULRESSO commercially in the U.S. in June 2019. The Company has a portfolio of other product candidates with a current focus on modulating two critical central nervous system (“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 biotechnology 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 the marketing and sale of pharmaceutical products; the potential for development by third parties of new technological innovations that may compete with the Company’s products and product candidates; the dependence on key personnel; the challenges of protecting proprietary technology; the need to comply with government regulations; the high costs of drug development; the impact of the COVID-19 pandemic on its operations and financial condition; and the uncertainty of being able to secure additional capital when needed to fund operations. Under Accounting Standards Update (“ASU”) No. 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 or other sources of funding 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. The Company expects that, based on its current operating plans, the Company’s existing cash, cash equivalents and marketable securities will be sufficient to fund its currently planned operations for at least the next 12 months from the filing date of this Annual Report. At some point after that time, the Company anticipates it will require additional financing to fund its future operations. Even if the Company believes it has sufficient funds for its current or future operating plans, the Company may seek to raise additional capital if market conditions are favorable or in light of other strategic considerations. COVID-19 The ongoing COVID-19 pandemic has caused and may continue to cause major disruptions to businesses and economies worldwide. The rapid spread of COVID-19 in the U.S. has resulted in a significant reduction in patient demand for ZULRESSO and in the number of sites available to administer ZULRESSO. This has had a negative impact on the Company’s revenue from sales of ZULRESSO. While there have been no material disruptions to date, any prolonged material disruptions to the work of the Company’s employees, suppliers, contract manufacturers, or vendors as a result of the COVID-19 pandemic could negatively impact the Company’s activities, availability of supplies, or operating results. Similarly, any material disruption to the Company’s development activities as a result of the COVID-19 pandemic may cause delays, increase the Company’s costs and impact the Company’s operating results. In addition, the COVID-19 pandemic initially caused major volatility in capital markets and has caused a significant global economic downturn, and the Company’s ability to access the capital markets in the future could be negatively impacted if the adverse effects of the pandemic continue.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
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 consolidated financial statements. Basis of Presentation The accompanying consolidated financial statements include those of the Company and its subsidiaries after elimination of all intercompany accounts and transactions. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the U.S. (“GAAP”). 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. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including sales, expenses, reserves and allowances, manufacturing, clinical trials, research and development costs and employee-related amounts, will depend on future developments that are highly uncertain, including developments related to the scope and duration of the pandemic; the duration and severity of precautionary measures taken to curb the spread of COVID-19, the length, location and frequency of surges or waves of COVID-19 cases and the timing and success of the roll-out of vaccines for COVID-19, and any return to normal business operations across the U.S . The Company has made estimates of the impact of the COVID-19 pandemic within its consolidated financial statements, and there may be changes to those estimates in future periods. 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 December 31, 2020, cash equivalents were comprised of commercial paper, money market funds and U.S. treasury securities. As of December 31, 2019, cash equivalents were comprised of commercial paper 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 marketable securities 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 the accumulated other comprehensive items in stockholders’ equity. When the fair value is below the amortized cost of the asset, an estimate of expected credit losses is made. The credit-related impairment amount is recognized in net income; the remaining impairment amount and unrealized gains are reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Credit losses are recognized through the use of an allowance for credit losses account and subsequent improvements in expected credit losses are recognized as a reversal of an amount in the allowance account. If the Company has the intent to sell the security or it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis, then the allowance for the credit loss is written-off and the excess of the amortized cost basis of the asset over its fair value is recorded in net income. Regardless of the Company’s intent to sell a security, it performs additional analysis on all securities with unrealized losses to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where the Company does not expect to receive cash flows sufficient to recover the amortized cost basis of a security. Accounts Receivable The Company’s trade accounts receivable consist of amounts due from specialty distributors, specialty pharmacies, and medically-supervised healthcare settings that have been certified under a Risk Evaluation and Mitigation Strategy (“REMS”) program in the U.S. related to sales of ZULRESSO and have standard payment terms that generally require payment within 30 to 90 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 makes judgments as to its ability to collect outstanding receivables and provides an allowance for receivables when appropriate. Trade accounts receivable are included in prepaid expenses and other current assets on the consolidated balance sheets. As of December 31, 2020, the Company has not provided any allowance for bad debts against the trade accounts receivable, and the amount of trade accounts receivable was not significant. 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 income (loss). Inventory is included in prepaid expenses and other current assets on the consolidated balance sheets and the amount was not significant as of December 31, 2020. 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 income (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. Property and Equipment Property and equipment are recorded at cost and depreciated over their estimated useful lives using the straight-line method. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is credited or charged to income. Repairs and maintenance costs are expensed as incurred. Intangible assets The Company had no intangible assets as of December 31, 2018. The Company received FDA approval for ZULRESSO on March 19, 2019 (“CyDex”) . 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 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 the right-of-use operating asset; operating lease liability, current portion; and operating lease liability, net of current portion in the Company’s 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. Variable lease payments are the amounts owed by the Company to a lessor that are not fixed, such as reimbursement for common area maintenance and utilities costs for facility leases and maintenance and tolls for leased vehicles. Variable lease payments are expensed when incurred. Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value 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 years ended December 31, 2020 and 2019 . Research and Development Costs and Accruals 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 billing terms under these contracts do not coincide with the timing of when the work is performed, the Company is required to make estimates of outstanding obligations to those third parties as of the end of the reporting period Patent Costs The Company expenses patent costs as incurred and classifies such costs as selling, general and administrative expenses in the accompanying consolidated statements of operations and comprehensive income (loss). Stock-Based Compensation The Company recognizes compensation expense for stock-based awards, including grants of stock options and restricted stock units, made to employees and non-employee directors based on the estimated fair value on the date of grant, over the requisite service period. The Company recognizes stock-based compensation expense for only the portion of awards that are expected to vest. Effective January 1, 2019, the Company recognizes compensation expense for stock-based awards, including grants of stock options and restricted stock units, 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 using 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. For the years ended December 31, 2019 and 2018, 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. Effective January 1, 2020, the Company began using the historical volatility of only its common stock, as there is adequate historical data 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 the options granted to non-employee consultants was determined based on the contractual term of the options, and since January 1, 2019, the “simplified” method has been 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. Treasury Stock The Company records treasury stock at cost. Treasury stock consists of shares received from an employee as consideration for exercises of stock options. Basic and Diluted Net Income (Loss) Per Share Basic net income (loss) per share is computed by dividing the net income (loss) by the weighted average number of shares of common stock that were outstanding during the period. Diluted net income (loss) per share is computed by adjusting the weighted average number of shares of common stock that were outstanding during the period for the dilutive effect of common stock equivalents outstanding for the period by using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per share is the same as basic net loss per share, because dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss for the years ended December 31, 2019 and 2018. Risks and Uncertainties The product candidates developed by the Company require approvals from the U.S. Food and Drug Administration or foreign regulatory agencies prior to commercial sales. There can be no assurance that the current and future product candidates of the Company will receive the necessary approvals. If the Company fails to successfully complete clinical development and generate results sufficient to file for regulatory approval or is denied approval or approval is delayed, it may have a material adverse impact on the Company’s business and its financial statements. Concentration of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company maintains accounts for all cash and cash equivalents at accredited financial institutions, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. The Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs. Income Taxes The Company accounts for income taxes under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted rates in effect for the year in which these temporary differences are expected to be recovered or settled. Valuation allowances are provided if, based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions in accordance with the provisions of Accounting Standards Codification (“ASC”) Topic 740, “ Income Taxes 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 December 31, 2020 and 2019 were carried at fair value, determined according to the fair value hierarchy; see Note 3, Fair Value Measurements. The carrying amounts reflected in the consolidated balance sheets for accounts payable and accrued expenses approximate their fair values due to their short-term maturities at December 31, 2020 and 2019, respectively. Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The singular focus of the Company is developing and commercializing novel medicines with the potential to transform the lives of people with debilitating disorders of the brain. Comprehensive Income (Loss) Comprehensive income (loss) includes net income (loss) and other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. Revenue Recognition The Company generates revenue from the sale of ZULRESSO, which was approved by the FDA in March 2019 and the Company subsequently began selling in June 2019, and from collaboration and supply agreements with the Company’s collaborators. To date, revenue from collaboration agreements has come from initial, upfront payments allocated to licenses of intellectual property delivered to the Company’s collaborators and from the supply of material for clinical trials under a supply agreement Under ASC Topic 606, “ Revenue from Contracts with Customers 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. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, they are considered performance obligations. The exercise of a material right may be accounted for as a contract modification or as a continuation of the contract for accounting purposes. 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 the consideration promised in a contract includes a variable amount, the Company estimates the amount of consideration to which it will be entitled in exchange for transferring the promised goods or services to a customer. The Company determines the amount of variable consideration by using the expected value method or the most likely amount method. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. 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. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment. 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 arrangements with Shionogi and Biogen and concluded that a significant financing component does not exist for either arrangement. 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. Revenue from the Company’s collaboration agreement with Shionogi has come from initial, upfront consideration upon execution of the agreement and for the supply of drug product for Shionogi’s clinical trials. Revenue from the Company’s collaboration agreement with Biogen has come from initial, upfront consideration related to the execution of the license and collaboration agreement. For additional information, refer to Note 6, Collaboration Agreements 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 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 income (loss). The Company expenses incremental costs of obtaining a contract as incurred if the expected amortization period of the asset would be less than one year. If the Company 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 December 31, 2020, as customer invoicing generally occurs before or at the time of revenue recognition. The Company did not have any contract liabilities at December 31, 2020, 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 updates its estimates and records 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 discounts resulting from contractual commitments to sell products to eligible healthcare settings 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 eligible healthcare settings. 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 eligible healthcare settings, 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 sheets. 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 ZULRES

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The Company’s cash equivalents are classified within Level 1 and Level 2 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 in Note 2, Summary of Significant Accounting Policies, 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 cash equivalents and marketable securities as of December 31, 2020 and 2019: December 31, 2020 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 $ 1,661,082 $ 1,637,609 $ 23,473 $ — Total cash equivalents 1,661,082 1,637,609 23,473 — Marketable securities: U.S. government securities 160,588 — 160,588 — U.S. corporate bonds 123,107 — 123,107 — International corporate bonds 57,676 — 57,676 — U.S. commercial paper 45,963 — 45,963 — International commercial paper 51,133 — 51,133 — Total marketable securities 438,467 — 438,467 — $ 2,099,549 $ 1,637,609 $ 461,940 $ — December 31, 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 $ 126,705 $ 65,414 $ 61,291 $ — Total cash equivalents 126,705 65,414 61,291 — Marketable securities: U.S. government securities 205,328 — 205,328 — U.S. corporate bonds 429,845 — 429,845 — International corporate bonds 142,998 — 142,998 — U.S. commercial paper 52,261 — 52,261 — International commercial paper 51,256 — 51,256 — Total marketable securities 881,688 — 881,688 — $ 1,008,393 $ 65,414 $ 942,979 $ — During the years ended December 31, 2020 and 2019, 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 December 31, 2020 and 2019: December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Credit Losses Fair Value (in thousands) Assets: U.S. government securities $ 160,589 $ 11 $ (12 ) $ — $ 160,588 U.S. corporate bonds 122,882 240 (15 ) — 123,107 International corporate bonds 57,485 200 (9 ) — 57,676 U.S. commercial paper 45,963 — — — 45,963 International commercial paper 51,133 — — — 51,133 $ 438,052 $ 451 $ (36 ) $ — $ 438,467 December 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Assets: U.S. government securities $ 205,172 $ 176 $ (20 ) $ 205,328 U.S. corporate bonds 429,148 797 (100 ) 429,845 International corporate bonds 142,568 457 (27 ) 142,998 U.S. commercial paper 52,252 14 (5 ) 52,261 International commercial paper 51,253 5 (2 ) 51,256 $ 880,393 $ 1,449 $ (154 ) $ 881,688 As of December 31, 2020 and 2019, all marketable securities held by the Company had remaining contractual maturities of one year or less, except for corporate bonds with a fair value of $5.1 million and $137.1 million, respectively, that had maturities of one to two years. As of December 31, 2020 and 2019, the marketable securities in a loss position have a maturity of less than one year. There have been no impairments of the Company’s assets measured and carried at fair value during the years ended December 31, 2020 and 2019.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	4. Balance Sheet Components Property and Equipment, net Property and equipment, net consists of the following: December 31, 2020 2019 (in thousands) Computer hardware and software $ 2,758 $ 2,830 Furniture and equipment 1,865 1,828 Leasehold improvements 9,220 8,967 13,843 13,625 Less: Accumulated depreciation (7,088 ) (4,499 ) $ 6,755 $ 9,126 Depreciation expense for the years ended December 31, 2020, 2019 and 2018 was $2.6 million, $2.3 million and $1.1 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: December 31, 2020 2019 (in thousands) Accrued research and development costs $ 34,398 $ 46,940 Restructuring 203 - Employee-related 14,566 22,011 Professional services 5,184 16,720 Other 500 947 $ 54,851 $ 86,618

Leases, Commitments and Conting

Leases, Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Leases, Commitments and Contingencies	5. Leases, Commitments and Contingencies Operating Leases The Company has leases for office space and certain equipment. All of the leases recorded on the consolidated balance sheets are operating leases. The Company’s leases have remaining lease terms ranging from less than one year to nearly four years. Some of the leases include options to extend the leases for up to five years. 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. As of January 1, 2018, the Company leased office space in two multi-tenant buildings in Cambridge, Massachusetts, consisting of 54,943 square feet in the first building under an operating lease that will expire on August 15, 2024 and 19,805 square feet in the second building under an operating lease that will expire on February 28, 2022. 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 for office space in a third multi-tenant building in Cambridge, Massachusetts. The amount of square feet of office space is 15,975 square feet and the lease period began on March 1, 2019. The term for this lease was initially scheduled to expire on February 29, 2024. Effective February 1, 2021, the Company terminated this lease. In March 2019, the Company entered into the Eighth Amendment to the lease for office space in the first multi-tenant 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 . From June 2018 to January 2019, the Company entered into leases for vehicles for field-based employees. These leases were determined to be operating leases and a right-of-use operating asset in the amount of $5.3 million was recorded on the balance sheet upon implementation of the new lease standard on January 1, 2019. The leases were for a term of three years and were to expire on various dates through January 31, 2022. During the year ended December 31, 2020, these leases were terminated as part of the April 2020 restructuring (see Note 13, Restructuring), and the remaining asset of $2.3 million and the liabilities related to these leases were de-recognized upon termination of the leases, and the restricted cash of $0.7 million related to these leases was returned to the Company by the lessor. The following table shows the amounts of operating leases in the balance sheets as of December 31, 2020 and 2019: December 31, Balance sheet location Balance sheet caption 2020 2019 (in thousands) Assets Right-of-use operating asset Right-of-use operating asset $ 25,064 $ 33,771 Liabilities Current operating lease liabilities Operating lease liability, current portion 8,662 10,244 Long-term operating lease liabilities Operating lease liability, net of current portion 19,438 26,848 Total operating lease liabilities $ 28,100 $ 37,092 Lease expense by lease type recognized during the years ended December 31, 2020 and 2019 was as follows: Year Ended December 31, 2020 2019 (in thousands) Operating lease cost $ 8,838 $ 9,804 Variable lease cost 2,285 2,675 Short-term lease cost 74 438 $ 11,197 $ 12,917 Rent expense for the year ended December 31, 2018 was $6.5 million. 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 as expense 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. The minimum lease payments are expected to be as follows: Years Ending December 31, (In thousands) 2021 $ 8,662 2022 8,898 2023 9,105 2024 5,560 2025 - Thereafter - Total lease payments 32,225 Less imputed interest (4,125 ) Present value of operating lease liabilities $ 28,100 The weighted average remaining lease term and weighted average discount rate of the Company’s operating leases are as follows: December 31, 2020 Weighted average remaining lease term in years 3.61 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 consolidated statements of cash flows is as follows: Year Ended December 31, 2020 2019 (in thousands) Cash paid for amounts included in the measurement of lease liabilities $ 9,231 $ 9,946 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ - $ 872 Lease asset de-recognized upon lease cancellation Operating leases $ 2,310 $ - During the year ended December 31, 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. During the year ended December 31, 2020, the one right-of-use asset was de-recognized. The leases for vehicles for field-based employees were terminated as part of the April 2020 restructuring (see Note 13, Restructuring), and the remaining asset of $2.3 million and the liabilities related to these leases were de-recognized upon termination of the leases. License Agreements CyDex License Agreement In September 2015, the Company and CyDex, a wholly owned subsidiary of Ligand Pharmaceuticals, Inc., 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 such product candidate is successfully developed in the future Under the amended and restated license agreement with CyDex, the Company agreed to make milestone payments 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 December 31, 2020, the Company has recorded research and development expense and made cash payments of $2.3 million related to these clinical development and regulatory milestones; has recorded research and development expense and accrued expenses of $1.3 million related to these clinical development milestones and has recorded an intangible asset and made a cash payment of $3.0 million related to these regulatory milestones. For the year ended December 31, 2018, additional clinical development milestones were met for the brexanolone program under the license agreement with CyDex, and accordingly, the Company recorded research and development expense and made cash payments totaling $0.8 million. For the year ended December 31, 2019, the Company recorded an intangible asset of $3.0 million related to a regulatory milestone for the brexanolone program under the license agreement with CyDex. For the year ended December 31, 2020, additional clinical development milestones were met for the brexanolone program under the license agreement with CyDex, and accordingly, the Company recorded research and development expense and accrued expenses totaling $1.3 million. As of December 31, 2020, the Company has made no milestone payments related to clinical development or regulatory milestones for SAGE-689 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 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. The Company paid to the Regents clinical development milestones of $0.1 million prior to December 31, 2015; no other milestones are outstanding under this non-exclusive license agreement. 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 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 December 31, 2020, 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 year ended December 31, 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. For the year ended December 31, 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. For the year ended December 31, 2020, the Company did not record any expense or make any milestone or royalty payments under the license agreements with the Regents. 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 December 31, 2020, the Company has recorded research and development expense and made a cash payment of $50,000 related to these clinical 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 years ended December 31, 2020, 2019 and 2018, the Company did not record any expense or make any milestone payments under the license agreement with Washington University.

Collaboration Agreements

Collaboration Agreements	12 Months Ended
	Dec. 31, 2020
Shionogi Collaboration Agreement [Member]
Collaboration Agreement with Shionogi	6. Collaboration Agreements Shionogi In June 2018 Existing Partner Territory Under the terms of the collaboration agreement, Shionogi will be responsible for all clinical development, regulatory filings and commercialization of zuranolone for MDD, and potentially other indications, in the Existing Partner Territory Existing Partner Territory Existing Partner Territory The Company concluded that Shionogi meets the definition to be accounted for as a customer because the Company is delivering intellectual property and know-how rights for the zuranolone 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 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 Topic 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 satisfied each performance obligation. The Company determined that the performance obligations in the contract included the license to zuranolone and the supply of certain materials during the clinical development phase, which includes the supply of active pharmaceutical ingredient, or API. The performance obligation related to the license to zuranolone was determined to be distinct from other performance obligations and therefore was a separate performance obligation for which control was transferred upon signing. The obligation to provide certain clinical materials, including API for use during the development period, was determined to be a separate performance obligation. Given that Shionogi is not obligated to purchase any minimum amount or quantities of commercial API, the supply of API to Shionogi for commercial use was determined to be an option for Shionogi, rather than a performance obligation of the Company at contract inception and will be accounted for if and when exercised. The Company also determined that there was no separate material right in connection with the supply of API for commercial use as the expected pricing was not at a discount. Given this fact pattern, the Company has concluded the agreement has two performance obligations. Under the clinical supply agreement, the Company will manufacture and supply to Shionogi (i) clinical quantities of API reasonably required by Shionogi for the development of licensed products in the Shionogi territory under the collaboration and license agreement and (ii) quantities of drug product reasonably required for use by Shionogi in Phase 1 clinical trials of zuranolone in the Shionogi territory under the collaboration and license agreement, in the quantities agreed to by the parties. Collaboration revenue from the clinical supply agreement, which excludes the $90.0 million upfront payment, pertains to the clinical material sold under the terms of the clinical supply agreement. The Company records the costs related to the clinical supply agreement in research and development expense on its consolidated statements of operations and comprehensive income (loss). 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, which was in the three months ended June 30, 2018. 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 re - evaluate 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. Biogen In November 2020, the Company entered into a global collaboration and license agreement with Biogen (the “Biogen Collaboration Agreement”) to jointly develop and commercialize SAGE-217 products for MDD, PPD and other disorders and SAGE-324 products for essential tremor and other disorders. Concurrently, the Company also entered into a Stock Purchase Agreement with BIMA (the “Biogen Stock Purchase Agreement”) to purchase shares of the Company’s common stock. The Biogen Collaboration Agreement became effective on December 28, 2020 (the “Effective Date”). Under the terms of the Biogen Collaboration Agreement, the Company granted Biogen co-exclusive licenses to develop and commercialize SAGE-217 products and SAGE-324 products (each, a “Product Class” and together, the “Licensed Products”) in the U.S., an exclusive license to develop and commercialize SAGE-217 products in all countries of the world other than the Existing Partner Territory In connection with the effectiveness of the Biogen Collaboration Agreement and the closing of the sale of shares to Biogen in December 2020, the Company received $1.5 billion in consideration, comprised of an upfront payment of $875.0 million and the $650.0 million purchase price for 6,241,473 newly issued shares of the Company’s common stock (the “Biogen Shares”). The Company is eligible to receive additional payments of up to $1.6 billion if certain regulatory and commercial milestones are achieved. The potential future milestone payments for SAGE-217 products include up to $475.0 million for the achievement of specified regulatory and commercial milestones and up to $300.0 million for the achievement of specified net sales milestones. The potential future milestone payments for SAGE-324 products include up to $520.0 million for the achievement of specified regulatory and commercial milestones and up to $300.0 million for the achievement of specified net sales milestones. The Company is also eligible to receive tiered royalties on net sales of SAGE-217 products and SAGE-324 products in the Biogen Territory at percentage rates ranging from the high teens to low twenties. Due to the uncertainty of pharmaceutical development and the high historical failure rates generally associated with drug development, the Company may never receive any milestone payments or any royalty payments under the Biogen Collaboration Agreement. Development and commercialization activities in the U.S. will be conducted pursuant to plans agreed to by the Company and Biogen and overseen by a joint steering committee that will consist at all times of an equal number of representatives of each party. The Company and Biogen will share equally in the costs for development and commercialization, as well as the profits and losses, in the U.S., subject to the Company’s opt-out right described below. Biogen will be solely responsible for all development activities and costs related to any development and commercialization of SAGE-217 products and SAGE-324 products for the Biogen Territory and the Company will receive royalties on any sales in the Biogen Territory, as mentioned above. The Company will supply API and bulk drug product for the Biogen Territory and active pharmaceutical ingredient and final bulk drug product for the U.S. to support development and commercialization activities. Biogen has the right to assume manufacturing responsibilities for active pharmaceutical ingredient at any time during the agreement and will, within a reasonable period of time after the Effective Date, assume manufacturing responsibility for bulk drug product for the Biogen Territory. Unless terminated earlier, the Biogen Collaboration Agreement will continue on a Licensed Product-by-Licensed Product and country-by-country basis until the date on which (a) in any country in the Biogen Territory, the royalty term has expired for all Licensed Products in a Product Class in such country, and (b) for the U.S., the parties agree to permanently cease to commercialize all Licensed Products in a Product Class. Biogen also has the right to terminate the Biogen Collaboration Agreement for convenience upon advance written notice. The Company has an opt-out right to convert the co-exclusive licenses in the U.S. to an exclusive license to Biogen on a Product Class-by-Product Class basis. Following the exercise of the opt-out right, the Company would no longer share equally in the profits and losses in the U.S. and would be entitled to receive certain royalty payments at percentage rates ranging from the high teens to low twenties additional sales milestones. The Company concluded that the Biogen Collaboration Agreement and the Biogen Stock Purchase Agreement should be combined and treated as a single arrangement for accounting purposes as the agreements were entered into contemporaneously and in contemplation of one another. The Company determined that the combined agreements had elements that were within the scope of Topic 606 and Topic 808. As of the Effective Date, the Company identified the following promises in the Biogen Collaboration Agreement that were evaluated under the scope of Topic 606: delivery of (i) a co-exclusive license for SAGE-217 products in the U.S.; (ii) an exclusive license for SAGE-217 products in the Biogen Territory; (iii) a co-exclusive license for SAGE-324 products in the U.S.; (iv) an exclusive license for SAGE-324 products in all countries of the world other than the U.S.; (v) the clinical manufacturing supply of active pharmaceutical ingredient and bulk drug product for SAGE-217 products in the Biogen Territory; and (vi) the clinical manufacturing supply of active pharmaceutical ingredient and bulk drug product for SAGE-324 products in the Biogen Territory. The Company also evaluated whether certain options outlined within the Biogen Collaboration Agreement represented material rights that would give rise to a performance obligation and concluded that none of the options convey a material right to Biogen and therefore are not considered separate performance obligations within the Biogen Collaboration Agreement. The Company assessed the above promises and determined that the co-exclusive licenses for SAGE-217 products and SAGE-324 products in the U.S. are reflective of a vendor-customer relationship and therefore represent performance obligations within the scope of Topic 606. The co-exclusive license for SAGE-217 products and SAGE-324 products in the U.S. are considered functional intellectual property and distinct from other promises under the contract. The exclusive licenses for SAGE-217 products and SAGE-324 products in the Biogen Territory are considered functional licenses that are distinct in the context of the Biogen Collaboration Agreement as Biogen can benefit from the licenses on its own or together with other readily available resources. As the co-exclusive licenses in the U.S. and the exclusive licenses in the Biogen Territory are delivered at the same time, they are considered one performance obligation at contract inception. The clinical manufacturing supply of active pharmaceutical ingredient and bulk drug product for SAGE-217 products and SAGE-324 products for the Biogen Territory are considered distinct in the context of the Biogen Collaboration Agreement as Biogen can benefit from the manufacturing services together with the licenses transferred by the Company at the inception of the agreement. Therefore, each represents a separate performance obligation within a contract with a customer under the scope of Topic 606 at contract inception. The Company considers the collaborative activities associated with the co-development, co-commercialization, and co-manufacturing of SAGE-217 products and SAGE-324 products in the U.S. to be separate units of account within the scope of Topic 808 as the Company and Biogen are both active participants in the development and commercialization activities and are exposed to significant risks and rewards that are dependent on the development and commercial success of the activities in the arrangement. The Company determined the transaction price under Topic 606 at the inception of the Biogen Collaboration Agreement to be $1.1 billion, consisting of the upfront payment of $875.0 million plus $232.5 million in excess proceeds from the equity investment under the Biogen Stock Purchase Agreement, when measured at fair value, plus future variable consideration for manufacturing supply of clinical active pharmaceutical ingredient and bulk drug product for the Biogen Territory. The amount of variable consideration related to the future manufacturing services was not material. The Company determined that any variable consideration related to clinical development and regulatory milestones is deemed to be fully constrained and therefore excluded from the transaction price due to the high degree of uncertainty and risk associated with these potential payments, as the Company determined that it could not assert that it was probable that a significant reversal in the amount of cumulative revenue recognized will not occur. The Company also determined that royalties and sales milestones relate solely to the licenses of intellectual property and are therefore excluded from the transaction price under the sales- or usage-based royalty exception of Topic 606. Revenue related to these royalties and sales milestones will only be recognized when the associated sales occur, and relevant thresholds are met. As noted above, the Company identified three performance obligations in the Biogen Collaboration Agreement: (i) the delivery of the co-exclusive licenses for SAGE-217 products and SAGE-324 products in the U.S. and the exclusive licenses for SAGE-217 products and SAGE-324 products in the Biogen Territory; (ii) the clinical manufacturing supply of active pharmaceutical ingredient and bulk drug product for SAGE-217 products in the Biogen Territory; and (iii) the clinical manufacturing supply of the active pharmaceutical ingredient and bulk drug product for SAGE-324 products in the Biogen Territory. The selling price of each performance obligation in the Biogen Collaboration Agreement was determined based on the Company’s SSP with the objective of determining the price at which it would sell such an item if it were to be sold regularly on a standalone basis. The Company allocated the variable consideration related to the manufacturing obligations to the future clinical supply of SAGE-217 products and SAGE 324 products in the Biogen Territory and the remaining fixed consideration to the license obligation. The variable consideration related to the manufacturing obligations was not material. As such, the entirety of the $1.1 billion fixed consideration of the transaction price has been allocated to the transfer of the co-exclusive licenses for SAGE-217 products and SAGE-324 products in the U.S. and the exclusive licenses for SAGE-217 products and SAGE-324 products in the Biogen Territory. The Company recognizes revenue for the license performance obligations at a point in time, that is upon transfer of the licenses to Biogen. As control of these licenses was transferred on the Effective Date and Biogen could begin to use and benefit from the licenses, the Company recognized $1.1 billion of license revenue during the year ended December 31, 2020 under the Biogen Collaboration Agreement. The Company will recognize revenue for the clinical manufacturing supply obligations at a point in time, that is upon the delivery of the supply to Biogen. Accounting for the Biogen Stock Purchase Agreement In connection with the execution of the Biogen Collaboration Agreement, the Company and BIMA entered into the Biogen Stock Purchase Agreement. Pursuant to the Biogen Stock Purchase Agreement, the Company sold the Biogen Shares to BIMA at a price of approximately $104.14 per share, which represented a 40 percent premium over the 30-day volume-weighted average share price as of the last trading day prior to the date the Biogen Collaboration Agreement and Biogen Stock Purchase Agreement were executed in November 2020, for aggregate consideration of $650.0 million. The sale of the shares to BIMA closed on December 31, 2020. The Biogen Stock Purchase Agreement includes certain standstill provisions, lock-up restrictions, and a voting agreement with respect to the Biogen Shares. Pursuant to the terms of the Biogen Stock Purchase Agreement, BIMA has agreed not to, and to cause its affiliates not to, directly or indirectly acquire the Company’s securities, seek or propose a tender or exchange offer or merger between the Company and Biogen, solicit proxies or consents with respect to any matter, or undertake other specified actions, in each case subject to specified conditions. The standstill restrictions terminate on the earliest of (i) a specified regulatory milestone under the Biogen Collaboration Agreement, (ii) the date one year following the termination of the Biogen Collaboration Agreement and (iii) the seventh anniversary of the Effective Date. BIMA has also agreed not to, and to cause its affiliates not to, sell or transfer any of the Biogen Shares for a period of eighteen months and to limit sales and transfers of the Biogen Shares for an additional eighteen month period, in each case subject to specified conditions and exceptions. The Company determined the fair value of the common shares issued using an option pricing valuation model to take into consideration the holding period restrictions. The fair value of the Company’s common stock was considered a level 2 fair value measurement within the fair value hierarchy. The most significant assumptions within the model are the Company’s stock price, the term of the restrictions and the stock price volatility, which is based upon a blend of historical and implied volatility of the Company’s stock. Based on the fair value adjustments made by management, the fair value of the shares issued was determined to be $ 417.5 million, which was $ 232.5 million less than the proceeds received from B IMA for the issuance of the Company’s common stock under the Biogen S tock P urchase A greement . As such, the $232.5 million in excess proceeds has been included in the $ 1.1 billion transaction price of the Biogen Collaboration Agreement determined above.

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Preferred Stock	7 . Preferred Stock The Board of Directors of the Company is authorized, without action by the stockholders, to designate and issue up to an aggregate of 5,000,000 shares of preferred stock in one or more series. The Board of Directors of the Company can designate the rights, preferences and privileges of the shares of each series and any of its qualifications, limitations or restrictions. The Board of Directors of the Company may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of common stock. As of December 31, 2020 and 2019, the Company had no shares of preferred stock issued or outstanding and preferred stock was classified as stockholders’ equity.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2020
Text Block [Abstract]
Common Stock	8 . Common Stock As of December 31, 2020 and 2019, the Company authorized 120,000,000 shares of common stock with a par value of $0.0001 per share. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends, as may be declared by the Board of Directors, if any. As of December 31, 2020 and 2019, no dividends have been declared. On February 13, 2018, the Company completed the sale of 4,032,012 shares of its common stock at a price to the public of $164.00 per share, resulting in net proceeds to the Company of $631.2 million after deducting underwriting discounts and commissions 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 at a price to the public of $150.00 per share, resulting in net proceeds to the Company of $560.9 million after deducting underwriting discounts and commissions and offering costs paid by the Company. On December 31, 2020, the Company completed the sale of 6,241,473 shares of its common stock in a private placement to Biogen at a price to the public of approximately $104.14 per share, resulting in aggregate gross proceeds to the Company of $650.0 million. As of December 31, 2020, the Company had received 3,033 shares of the Company’s common stock from a then employee as proceeds for exercises of stock options. The total cost of shares held in treasury at December 31, 2020 was $0.4 million.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	9 . Stock-Based Compensation Equity Plans On July 2, 2014, the stockholders of the Company approved the 2014 Stock Option and Incentive Plan (the “2014 Plan”), which became effective immediately prior to the completion of the Company’s IPO. The 2014 Plan provides for the grant of restricted stock awards, restricted stock units, incentive stock options and non-statutory stock options. The 2014 Plan replaced the Company’s 2011 Stock Option and Grant Plan (the “2011 Plan”). The Company no longer grants stock options or other awards under its 2011 Plan, but any options outstanding under the 2011 Plan remain outstanding and effective in accordance with their terms. The 2014 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, 2020 , 2,075,087 shares of common stock, representing 4% of the Company’s outstanding shares of common stock as of December 31, 2019 , were added to the 2014 Plan . On December 15, 2016, the Board of Directors of the Company (the “Board”) approved the 2016 Inducement Equity Plan (as amended and restated, the “2016 Plan”). The 2016 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 Plan to increase the total number of shares reserved for issuance by 1,200,000 shares. Terms of equity grants, including vesting requirements, are determined by the Board or the Compensation Committee of the Board, subject to the provisions of the applicable plan. Options granted by the Company, that are not performance-based, are considered time-based because they generally vest based on the continued service of the grantee with the Company during a specified period following grant. These awards, when granted to employees, generally vest ratably over four years, with 25% cliff vesting at the one-year As of December 31, 2020, the total number of shares reserved under all equity plans was 12,535,574 and the total number of shares available for future issuance under all equity plans was 4,420,049 shares. Restricted Stock Units The table below summarizes activity relating to time-based restricted stock units and performance restricted stock units: Shares Outstanding as of December 31, 2019 333,243 Granted 1,022,276 Vested — Forfeited (397,824 ) Outstanding as of December 31, 2020 957,695 During the year ended December 31, 2017, the Company granted 32,500 time-based restricted stock units to certain employees of the Company. The Company did not grant time-based restricted stock units prior to January 1, 2017. These time-based restricted stock units vested ratably over two years, with vesting of 50% at both the one-year and two-year anniversary of the grant date, which was in February 2018 and 2019, respectively. The fair value of the time-based restricted stock units that vested during the years ended December 31, 2019 and 2018 was $2.0 million and $2.6 million, respectively. No time-based restricted stock units vested during the year ended December 31, 2020. During the year ended December 31, 2020, the Company granted 550,890 time-based restricted stock units to certain employees of the Company. These time-based restricted stock units will vest over two years, with 25% vesting at the one-year anniversary of the grant date and 75% vesting at the two-year anniversary of the grant date, which will be in April 2021 and April 2022, respectively. During the years ended December 31, 2019 and 2018, the Company granted no time-based restricted stock units. During the year ended December 31, 2018, the Company granted 71,400 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 year ended December 31, 2019, the Company granted 393,539 performance restricted stock units to employees of the Company . These performance restricted stock units are related to the achievement of certain clinical and regulatory development milestones related to product candidates and commercial milestones. During the year ended December 31, 2020, the Company granted 471,386 performance restricted stock units to employees of the Company. These performance restricted stock units are related to the achievement of certain clinical and regulatory development milestones related to product candidates and commercial milestones. Recognition of stock-based compensation expense associated with performance restricted stock units 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 year ended December 31, 2019, one milestone for grants of performance restricted stock units was achieved. This milestone represents 18% of the performance restricted stock units that were granted during the year ended December 31, 2019. The fair value of performance restricted stock units that vested during the year ended December 31, 2019 was $11.1 million. No performance restricted stock units vested during the years ended December 31, 2020 and 2018. At December 31, 2020, 957,695 restricted stock units were both outstanding and unvested, and the total unrecognized stock-based compensation expense related to those awards was $58.2 million. Option Rollforward The table below summarizes activity related to time-based and performance-based stock options: Shares Weighted Average Exercise Price Weighted Average Remaining Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2019 8,163,113 $ 106.30 7.75 $ 87,972 Granted 1,544,915 56.03 Exercised (118,325 ) 43.34 Forfeited (2,431,873 ) 121.28 Outstanding as of December 31, 2020 7,157,830 $ 91.41 6.91 $ 167,242 Vested and expected to vest as of December 31, 2020 6,469,905 $ 90.94 6.79 $ 153,562 Exercisable as of December 31, 2020 4,674,438 $ 89.51 6.09 $ 120,030 At December 31, 2020, the Company had unrecognized stock-based compensation expense related to its unvested time-based stock option awards of $120.5 million, which is expected to be recognized over the remaining weighted average vesting period of 1.76 years. The intrinsic value of stock options exercised during the years ended December 31, 2020, 2019 and 2018 was $2.1 million, $119.1 million and $98.3 million, respectively. Performance-Based Stock Options During the year ended December 31, 2018, the Company granted 524,003 options 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 commercial milestones. During the years ended December 31, 2020 and 2019, the Company granted no options to employees to purchase shares of common stock that contain performance-based vesting criteria. Recognition of stock-based compensation expense associated with 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 year ended December 31, 2018, a 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 year ended December 31, 2018, the Company recognized stock-based compensation expense related to this milestone of $6.9 million. During the year ended December 31, 2018, one milestone was achieved under stock options granted to employees. This milestone represents 33% of the performance-based options that were granted during the year ended December 31, 2017. During the year ended December 31, 2018, the Company recognized stock-based compensation expense related to this milestone of $4.4 million. During the year ended December 31, 2018, the remaining milestone for the performance-based option grants that were made during the years ended December 31, 2016 and December 31, 2015 was not met, and accordingly, those options were cancelled. This milestone represents 50% and 35% of the performance-based option grants that were made during the years ended December 31, 2016 and December 31, 2015, respectively. The Company recognized no stock-based compensation expense related to this milestone. During the year ended December 31, 2019, one commercial milestone was achieved under stock options granted to employees. Stock options with this milestone were granted during the years ended December 31, 2018 and 2017, respectively. 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 year ended December 31, 2019, the Company recognized stock-based compensation expense related to this milestone of $16.3 million. During the year ended December 31, 2020, no milestones were achieved under performance-based options. During the year ended December 31, 2020, one milestone for the performance-based option grants that were made during the year ended December 31, 2018 was not met, and accordingly, those options were cancelled. This milestone represents 19% of the performance-based option grants that were made during the year ended December 31, 2018. The Company recognized no stock-based compensation expense related to this milestone. As of December 31, 2020, 2019 and 2018, for performance-based option 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 not considered probable, and therefore no expense has been recognized related to these awards in the years ended December 31, 2020, 2019 and 2018, respectively. As of December 31, 2020, 288,575 performance-based stock options were both outstanding and unvested, and the total unrecognized stock-based compensation expense related to those awards was $20.6 million. Stock-Based Compensation Expense Stock-based compensation expense recognized during the years ended December 31, 2020, 2019 and 2018 was as follows: Year Ended December 31, 2020 2019 2018 (in thousands) Research and development $ 42,370 $ 62,931 $ 50,871 Selling, general and administrative 51,836 90,300 51,092 Restructuring 1,788 — — $ 95,994 $ 153,231 $ 101,963 Stock-based compensation expense recognized during the years ended December 31, 2020, 2019 and 2018 by award type was as follows: Year Ended December 31, 2020 2019 2018 (in thousands) Stock options $ 90,064 $ 140,517 $ 100,342 Restricted stock units 4,904 10,992 651 Employee stock purchase plan 1,026 1,722 970 $ 95,994 $ 153,231 $ 101,963 The stock-based compensation expense recorded for the restructuring in the year ended December 31, 2020 is the incremental amount related to modifying the exercise period for outstanding, vested option grants that had been made to employees who were terminated in the restructuring. For stock option awards, the fair value is estimated at the grant date using the Black-Scholes option-pricing model, taking into account the terms and conditions upon which options are granted. The fair value of the options is amortized on a straight-line basis for awards to employees over the requisite service period of the awards. For awards to non-employees, the fair value of the options was amortized on a graded basis through December 31, 2018, and starting on January 1, 2019, on a straight-line basis, over the requisite service period of the awards. The weighted average grant date fair value per share of stock options granted under the Company’s stock option plans during the years ended December 31, 2020, 2019 and 2018 was $37.53, $82.39 and $109.92, respectively. The fair value of each option granted under the Company’s equity plans has been calculated on the date of grant using the following weighted average assumptions: Year Ended December 31, 2020 2019 2018 Expected dividend yield 0 % 0 % 0 % Expected volatility 77.86 % 71.34 % 74.45 % Risk-free interest rate 0.97 % 2.21 % 2.68 % Expected term 5.98 years 6.05 years 6.04 years Expected dividend yield: the Company has not paid, and does not anticipate paying, any dividends in the foreseeable future. Risk-free interest rate: the Company determined the risk-free interest rate by using a weighted average equivalent to the expected term based on the U.S. Treasury yield curve in effect as of the date of grant. Expected volatility: 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 expected to continue to do so until such time as it has adequate historical data regarding the volatility of its common stock price for the duration of the expected term. Effective January 1, 2020, the Company began using the historical volatility of only its common stock, as there is adequate historical data for the duration of the expected term. Expected term (in years): the expected term represents the period that the Company’s stock option grants are expected to be outstanding. 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 the options granted to non-employee consultants was determined based on the contractual term of the options, and since January 1, 2019, the “simplified” method has been used. Under this approach, the weighted average expected life is presumed to be the average of the vesting term and the contractual term of the option. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from estimates. The Company estimates forfeitures based on historical terminations. For the years ended December 31, 2020, 2019 and 2018, the weighted-average forfeiture rates were 20.6%, 13.7% and 10.7%, respectively. Through December 31, 2018, for options granted to non-employees, the expected term is 10 years, which is the contractual term of each option. All other assumptions used to calculate the grant date fair value for non-employees are generally consistent with the assumptions used for options granted to employees. 2014 Employee Stock Purchase Plan On July 2, 2014, the Company’s stockholders approved the 2014 Employee Stock Purchase Plan, which had been previously approved by the Board of Directors. The 2014 Employee Stock Purchase Plan became effective upon the completion of the IPO. A total of 282,000 shares of common stock were authorized for issuance under this plan. As of December 31, 2020, 177,879 shares have been issued under this plan and 104,121 shares are available for issuance under this plan. At December 31, 2020, accrued expenses includes $0.3 million of stock-based compensation expense related to an enrollment period for which the related shares had not been issued as of December 31, 2020.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	10 . Net Income (Loss) Per Share Basic and diluted net income (loss) per share was calculated as follows for the years ended December 31, 2020, 2019 and 2018: Year Ended December 31, 2020 2019 2018 Basic net income (loss) per share: Numerator: Net income (loss) (in thousands) $ 606,073 $ (680,238 ) $ (372,882 ) Denominator: Weighted average common stock outstanding —basic 51,983,188 50,833,837 46,121,194 Effect of dilutive securities: Stock options 721,791 — — Restricted stock units 292,241 — — ESPP 5,895 — — Total dilutive securities 1,019,927 — — Weighted average common stock outstanding —diluted 53,003,115 50,833,837 46,121,194 Net income (loss) per share—basic $ 11.66 $ (13.38 ) $ (8.08 ) Net income (loss) per share—diluted $ 11.43 $ (13.38 ) $ (8.08 ) The following common stock equivalents outstanding as of December 31, 2020, 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: Year Ended December 31, 2020 2019 2018 Stock options 4,781,737 7,677,518 6,758,420 Restricted stock units — — 13,500 Employee stock purchase plan — 33,429 16,398 4,781,737 7,710,947 6,788,318 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.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	1 1 . Income Taxes Income (loss) before income tax expense consists of the following: Year Ended December 31, 2020 2019 2018 (in thousands) Domestic $ 639,986 $ (634,289 ) $ (296,040 ) Foreign (33,913 ) (45,949 ) (76,842 ) $ 606,073 $ (680,238 ) $ (372,882 ) There is no current or deferred provision for income taxes because the Company had historically incurred operating losses prior to the year ended December 31, 2020, which it has used to reduce both federal and state taxable income for the year ended December 31, 2020. As of December 31, 2020, the Company continues to maintain a full valuation allowance against its net deferred tax assets. The reported amount of income tax expense for the years differs from the amount that would result from applying domestic federal statutory tax rates to pretax losses primarily because of changes in valuation allowance . A reconciliation of the U.S. statutory rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2020 2019 2018 Tax due at statutory rate 21.0 % 21.0 % 21.0 % State taxes, net of federal 5.7 2.8 6.0 Biogen transaction-related items (10.1 ) — — Stock-based compensation 0.9 1.4 2.5 Foreign rate differential 1.2 (1.6 ) (4.3 ) Federal and state credits (1.5 ) 2.4 2.5 Change in valuation allowance (17.6 ) (25.8 ) (27.6 ) Other 0.4 0.5 (0.1 ) Federal and state rate change — (0.7 ) — 0.0 % 0.0 % 0.0 % The Biogen transaction-related items consist primarily of the excess proceeds from the equity investment under the Biogen Stock Purchase Agreement. Significant components of the Company’s net deferred tax assets at December 31, 2020 and 2019 are as follows: December 31, 2020 2019 (in thousands) Net operating losses $ 222,607 $ 348,848 Capitalized start-up costs 873 982 Tax credit carryforwards 90,460 80,088 Accrued expenses 3,157 4,055 Depreciation and amortization 1,614 2,002 Stock options 56,520 46,750 Right of use asset (5,981 ) (8,059 ) Lease liability 6,705 8,852 Other 148 (246 ) Total net deferred tax asset before valuation allowance 376,103 483,272 Valuation allowance (376,103 ) (483,272 ) Net deferred tax asset $ — $ — As of December 31, 2020, the Company had federal and state net operating loss carryforwards of $41.7 $438.4 2033 $40.7 $42.3 In response to the COVID-19 pandemic, the Coronavirus Aid, Relief and Economic Security Act (“the CARES Act”) was signed into law in the U.S. in March 2020. The CARES Act adjusted a number of provisions of the tax code, including the calculation and eligibility of certain deductions and the treatment of net operating losses and tax credits. The enactment of the CARES Act did not result in any material adjustment to the income tax provision for the year ended December 31, 2020, or to the net deferred tax assets as of December 31, 2020. As of December 31, 2020, net deferred tax assets before the valuation allowance decreased $107.2 million, primarily due to the utilization of federal and state net operating loss carryforwards to reduce federal and state taxable income for the year ended December 31, 2020. This decrease in net deferred tax assets was offset by a corresponding decrease in the valuation allowance. Management of the Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which are comprised principally of federal and state net operating loss and tax credit carryforwards. Under the applicable accounting standards, management has considered the Company’s history of losses and concluded that it is more likely than not that the Company will not recognize the benefits of its federal and state deferred tax assets. Accordingly, a full valuation allowance of $376.1 million and $483.3 million has been established at December 31, 2020 and 2019, respectively. The valuation allowance decreased by $107.2 million, increased by $174.9 million and increased by $102.9 million for the years ended December 31, 2020, 2019 and 2018, respectively, primarily due to utilization or generation of net operating losses. Pursuant to Section 382 of the Internal Revenue Code, and similar state tax law, certain substantial changes in the Company’s ownership may result in a limitation on the amount of net operating loss and tax credit carryforwards that may be used in future years. Utilization of the net operating loss and tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership change limitations that have occurred previously or that could occur in the future. These ownership changes may limit the amount of net operating loss and tax credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. The Company completed a Section 382 study through December 31, 2020. Based on the study, the Company underwent two ownership changes for Section 382 purposes which occurred on March 11, 2014 and December 31, 2015. As a result of the ownership changes, the Company’s net operating loss and tax credit carryforwards as of the ownership change dates are subject to limitation under Section 382; however, these limitations are not expected to cause any of the impacted net operating loss and tax credit carryforwards to expire unused. Any net operating losses or tax credits generated after the December 2015 change are not subject to this annual limitation. However, subsequent ownership changes, as defined by Section 382, may potentially further limit the amount of net operating loss and tax credit carryforwards that could be utilized to offset future taxable income and tax. The Company applies the authoritative guidance on accounting for and disclosure of uncertainty in tax positions, which requires the Company to determine whether a tax position of the Company is more likely than not to be sustained upon examination, including resolution of any related appeals of litigation processes, based on the technical merits of the position. For tax positions meeting the more likely than not threshold, the tax amount recognized in the financial statements is reduced by the largest benefit that has a greater than fifty percent likelihood of being realized upon the ultimate settlement with the relevant taxing authority. At December 31, 2020, 2019 and 2018, the Company had no unrecognized tax benefits. The Company’s policy is to record interest and penalties related to income taxes as part of the tax provision. As of December 31, 2020 and 2019, the Company had no accrued interest or penalties related to income taxes and no amounts have been recognized in the Company’s statement of operations. The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal, state and foreign jurisdictions, where applicable. There are currently no pending tax examinations, and the Company’s tax returns are generally open under statute from 2017 to the present. Tax attributes such as net operating losses and tax credits generated prior to 2017 and utilized in open years may still be adjusted upon examination.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2020
Postemployment Benefits [Abstract]
Employee Benefit Plan	1 2 . Employee Benefit Plan The Company maintains a 401(k) profit sharing plan (the “Plan”) for its employees. Each employee may elect to contribute a portion of his or her compensation to the Plan, subject to annual limits established by the Internal Revenue Service. For the years ended December 31, 2020, 2019 and 2018, the Company matched 50% of eligible contributions to the Plan up to 6% of employee contributions. For the years ended December 31, 2020, 2019 and 2018 the Company contributed to the Plan $2.2 million, $3.6 million and $1.8 million, respectively.

Restructuring

Restructuring	12 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Restructuring	1 3 . Restructuring In April 2020, the Company announced a restructuring plan to enable the Company to advance its corporate strategy and pipeline that included the elimination of approximately 53% of the Company’s workforce. The workforce reduction primarily affected the ZULRESSO commercial operation and related selling, general and administrative support functions. During the year ended December 31, 2020, the Company recorded $27.7 million of expense for restructuring, primarily for one-time termination benefits to the affected employees, primarily for cash payments of severance, healthcare benefits and outplacement assistance. Substantially all of the accrued restructuring charges were paid in cash as of December 31, 2020. Restructuring activity during the year ended December 31, 2020 was as follows: Restructuring accrual (in thousands) Balance as of January 1, 2020 $ - Restructuring expenses incurred 27,743 Cash paid (25,102 ) Non-cash activity (2,438 ) Balance as of December 31, 2020 $ 203

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	1 4 . Selected Quarterly Financial Data (Unaudited) The following table contains quarterly financial information for 2020 and 2019. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. 2020 First Quarter Second Quarter Third Quarter Fourth Quarter (1) Total (in thousands, except per share amounts) Total revenue $ 2,286 $ 1,089 $ 1,639 $ 1,109,186 $ 1,114,200 Total operating costs and expenses 133,910 140,056 108,797 135,211 517,974 Income (loss) from operations (131,624 ) (138,967 ) (107,158 ) 973,975 596,226 Net income (loss) (126,740 ) (136,347 ) (105,735 ) 974,895 606,073 Net income (loss) per share—basic $ (2.44 ) $ (2.63 ) $ (2.03 ) $ 18.71 $ 11.66 Net income (loss) per share—diluted $ (2.44 ) $ (2.63 ) $ (2.03 ) $ 18.19 $ 11.43 2019 First Quarter Second Quarter Third Quarter Fourth Quarter Total (in thousands, except per share amounts) Total revenue $ 465 $ 873 $ 3,570 $ 1,960 $ 6,868 Total operating costs and expenses 170,317 177,330 190,747 176,598 714,992 Loss from operations (169,852 ) (176,457 ) (187,177 ) (174,638 ) (708,124 ) Net loss (163,406 ) (168,221 ) (179,958 ) (168,653 ) (680,238 ) Net loss per share—basic and diluted $ (3.37 ) $ (3.28 ) $ (3.48 ) $ (3.25 ) $ (13.38 ) (1) In the fourth quarter of 2020, the Company recorded collaboration revenue of $1.1 billion related to the execution of the Biogen Collaboration Agreement and the Biogen Stock Purchase Agreement. For additional information, refer to Note 6, Collaboration Agreements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include those of the Company and its subsidiaries after elimination of all intercompany accounts and transactions. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the U.S. (“GAAP”).
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. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including sales, expenses, reserves and allowances, manufacturing, clinical trials, research and development costs and employee-related amounts, will depend on future developments that are highly uncertain, including developments related to the scope and duration of the pandemic; the duration and severity of precautionary measures taken to curb the spread of COVID-19, the length, location and frequency of surges or waves of COVID-19 cases and the timing and success of the roll-out of vaccines for COVID-19, and any return to normal business operations across the U.S . The Company has made estimates of the impact of the COVID-19 pandemic within its consolidated financial statements, and there may be changes to those estimates in future periods.
Cash Equivalents	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 December 31, 2020, cash equivalents were comprised of commercial paper, money market funds and U.S. treasury securities. As of December 31, 2019, cash equivalents were comprised of commercial paper 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 marketable securities 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 the accumulated other comprehensive items in stockholders’ equity. When the fair value is below the amortized cost of the asset, an estimate of expected credit losses is made. The credit-related impairment amount is recognized in net income; the remaining impairment amount and unrealized gains are reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Credit losses are recognized through the use of an allowance for credit losses account and subsequent improvements in expected credit losses are recognized as a reversal of an amount in the allowance account. If the Company has the intent to sell the security or it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis, then the allowance for the credit loss is written-off and the excess of the amortized cost basis of the asset over its fair value is recorded in net income. Regardless of the Company’s intent to sell a security, it performs additional analysis on all securities with unrealized losses to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where the Company does not expect to receive cash flows sufficient to recover the amortized cost basis of a security.
Accounts Receivable	Accounts Receivable The Company’s trade accounts receivable consist of amounts due from specialty distributors, specialty pharmacies, and medically-supervised healthcare settings that have been certified under a Risk Evaluation and Mitigation Strategy (“REMS”) program in the U.S. related to sales of ZULRESSO and have standard payment terms that generally require payment within 30 to 90 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 makes judgments as to its ability to collect outstanding receivables and provides an allowance for receivables when appropriate. Trade accounts receivable are included in prepaid expenses and other current assets on the consolidated balance sheets. As of December 31, 2020, the Company has not provided any allowance for bad debts against the trade accounts receivable, and the amount of trade accounts receivable was not significant.
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 income (loss). Inventory is included in prepaid expenses and other current assets on the consolidated balance sheets and the amount was not significant as of December 31, 2020. 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 income (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.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost and depreciated over their estimated useful lives using the straight-line method. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is credited or charged to income. Repairs and maintenance costs are expensed as incurred.
Intangible Assets	Intangible assets The Company had no intangible assets as of December 31, 2018. The Company received FDA approval for ZULRESSO on March 19, 2019 (“CyDex”) .
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 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 the right-of-use operating asset; operating lease liability, current portion; and operating lease liability, net of current portion in the Company’s 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. Variable lease payments are the amounts owed by the Company to a lessor that are not fixed, such as reimbursement for common area maintenance and utilities costs for facility leases and maintenance and tolls for leased vehicles. Variable lease payments are expensed when incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value
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 years ended December 31, 2020 and 2019 .
Research and Development Costs and Accruals	Research and Development Costs and Accruals 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 billing terms under these contracts do not coincide with the timing of when the work is performed, the Company is required to make estimates of outstanding obligations to those third parties as of the end of the reporting period
Patent Costs	Patent Costs The Company expenses patent costs as incurred and classifies such costs as selling, general and administrative expenses in the accompanying consolidated statements of operations and comprehensive income (loss).
Stock-Based Compensation	Stock-Based Compensation The Company recognizes compensation expense for stock-based awards, including grants of stock options and restricted stock units, made to employees and non-employee directors based on the estimated fair value on the date of grant, over the requisite service period. The Company recognizes stock-based compensation expense for only the portion of awards that are expected to vest. Effective January 1, 2019, the Company recognizes compensation expense for stock-based awards, including grants of stock options and restricted stock units, 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 using 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. For the years ended December 31, 2019 and 2018, 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. Effective January 1, 2020, the Company began using the historical volatility of only its common stock, as there is adequate historical data 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 the options granted to non-employee consultants was determined based on the contractual term of the options, and since January 1, 2019, the “simplified” method has been 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.
Treasury Stock	Treasury Stock The Company records treasury stock at cost. Treasury stock consists of shares received from an employee as consideration for exercises of stock options.
Basic and Diluted Net Loss Per Share	Basic and Diluted Net Income (Loss) Per Share Basic net income (loss) per share is computed by dividing the net income (loss) by the weighted average number of shares of common stock that were outstanding during the period. Diluted net income (loss) per share is computed by adjusting the weighted average number of shares of common stock that were outstanding during the period for the dilutive effect of common stock equivalents outstanding for the period by using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per share is the same as basic net loss per share, because dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss for the years ended December 31, 2019 and 2018.
Risks and Uncertainties	Risks and Uncertainties The product candidates developed by the Company require approvals from the U.S. Food and Drug Administration or foreign regulatory agencies prior to commercial sales. There can be no assurance that the current and future product candidates of the Company will receive the necessary approvals. If the Company fails to successfully complete clinical development and generate results sufficient to file for regulatory approval or is denied approval or approval is delayed, it may have a material adverse impact on the Company’s business and its financial statements.
Concentration of Credit Risk and of Significant Suppliers	Concentration of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and marketable securities. The Company maintains accounts for all cash and cash equivalents at accredited financial institutions, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. The Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.
Income Taxes	Income Taxes The Company accounts for income taxes under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted rates in effect for the year in which these temporary differences are expected to be recovered or settled. Valuation allowances are provided if, based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions in accordance with the provisions of Accounting Standards Codification (“ASC”) Topic 740, “ Income Taxes
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 December 31, 2020 and 2019 were carried at fair value, determined according to the fair value hierarchy; see Note 3, Fair Value Measurements. The carrying amounts reflected in the consolidated balance sheets for accounts payable and accrued expenses approximate their fair values due to their short-term maturities at December 31, 2020 and 2019, respectively.
Segment Data	Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The singular focus of the Company is developing and commercializing novel medicines with the potential to transform the lives of people with debilitating disorders of the brain.
Comprehensive Loss	Comprehensive Income (Loss) Comprehensive income (loss) includes net income (loss) and other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders.
Revenue Recognition	Revenue Recognition The Company generates revenue from the sale of ZULRESSO, which was approved by the FDA in March 2019 and the Company subsequently began selling in June 2019, and from collaboration and supply agreements with the Company’s collaborators. To date, revenue from collaboration agreements has come from initial, upfront payments allocated to licenses of intellectual property delivered to the Company’s collaborators and from the supply of material for clinical trials under a supply agreement Under ASC Topic 606, “ Revenue from Contracts with Customers 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. Arrangements that include rights to additional goods or services that are exercisable at a customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the customer and if so, they are considered performance obligations. The exercise of a material right may be accounted for as a contract modification or as a continuation of the contract for accounting purposes. 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 the consideration promised in a contract includes a variable amount, the Company estimates the amount of consideration to which it will be entitled in exchange for transferring the promised goods or services to a customer. The Company determines the amount of variable consideration by using the expected value method or the most likely amount method. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. 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. At the end of each subsequent reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment. 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 arrangements with Shionogi and Biogen and concluded that a significant financing component does not exist for either arrangement. 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. Revenue from the Company’s collaboration agreement with Shionogi has come from initial, upfront consideration upon execution of the agreement and for the supply of drug product for Shionogi’s clinical trials. Revenue from the Company’s collaboration agreement with Biogen has come from initial, upfront consideration related to the execution of the license and collaboration agreement. For additional information, refer to Note 6, Collaboration Agreements 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 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 income (loss). The Company expenses incremental costs of obtaining a contract as incurred if the expected amortization period of the asset would be less than one year. If the Company 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 December 31, 2020, as customer invoicing generally occurs before or at the time of revenue recognition. The Company did not have any contract liabilities at December 31, 2020, 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 updates its estimates and records 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 discounts resulting from contractual commitments to sell products to eligible healthcare settings 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 eligible healthcare settings. 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 eligible healthcare settings, 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 sheets. 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 financial assistance amounts for ZULRESSO and records any such amounts within accrued expenses on its consolidated balance sheets. 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 using demographics for patients who have registered and been approved for assistance. Any 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 on the consolidated balance sheets. Product Returns : Consistent with industry practice, the Company offers product return rights to direct customers for damaged, defective or expiring product, provided it is within a specified period around the product expiration date as set forth in the Company’s return goods policy. 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. The Company has experienced no product returns to date. 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. Collaborative arrangements The Company analyzes its collaboration arrangements to assess whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities and therefore within the scope of ASC Topic 808, Collaborative Arrangements
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2016-02, Leases (Topic 842) Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842 Codification Improvements to Topic 842, Leases Leases (Topic 842): Targeted Improvements Narrow-Scope Improvement for Lessors Leases (Topic 842): Codification Improvements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . This standard amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses for most financial assets and certain other instruments that are not measured at fair value through net income. For available-for-sale debt securities, entities are required to recognize an allowance for credit losses rather than a reduction in carrying value of the asset. Entities are no longer permitted to consider the length of time that fair value has been less than amortized cost when evaluating when credit losses should be recognized. The Company adopted the standard on the required effective date of January 1, 2020, on a prospective basis. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures . In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement The Company adopted the standard on the required effective date of January 1, 2020. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures In November 2018, the FASB issued ASU No. 2018-18, Clarifying the Interaction between Topic 808 and Topic 606 for as revenue under Topic 606 when the collaborative arrangement participant is a customer for a promised good or service that is distinct within the collaborative arrangement. The guidance also precludes entities from presenting amounts related to transactions with a collaborative arrangement participant that is not a customer as revenue, unless those transactions are directly related to third-party sales. The Company adopted the standard on the required effective date of January 1, 2020. This guidance did not have a significant impact on the Company’s consolidated financial statements and related disclosures . In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. 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)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Company's Cash Equivalents and Marketable Securities	The following tables summarize the Company’s cash equivalents and marketable securities as of December 31, 2020 and 2019: December 31, 2020 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 $ 1,661,082 $ 1,637,609 $ 23,473 $ — Total cash equivalents 1,661,082 1,637,609 23,473 — Marketable securities: U.S. government securities 160,588 — 160,588 — U.S. corporate bonds 123,107 — 123,107 — International corporate bonds 57,676 — 57,676 — U.S. commercial paper 45,963 — 45,963 — International commercial paper 51,133 — 51,133 — Total marketable securities 438,467 — 438,467 — $ 2,099,549 $ 1,637,609 $ 461,940 $ — December 31, 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 $ 126,705 $ 65,414 $ 61,291 $ — Total cash equivalents 126,705 65,414 61,291 — Marketable securities: U.S. government securities 205,328 — 205,328 — U.S. corporate bonds 429,845 — 429,845 — International corporate bonds 142,998 — 142,998 — U.S. commercial paper 52,261 — 52,261 — International commercial paper 51,256 — 51,256 — Total marketable securities 881,688 — 881,688 — $ 1,008,393 $ 65,414 $ 942,979 $ —
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 December 31, 2020 and 2019: December 31, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Credit Losses Fair Value (in thousands) Assets: U.S. government securities $ 160,589 $ 11 $ (12 ) $ — $ 160,588 U.S. corporate bonds 122,882 240 (15 ) — 123,107 International corporate bonds 57,485 200 (9 ) — 57,676 U.S. commercial paper 45,963 — — — 45,963 International commercial paper 51,133 — — — 51,133 $ 438,052 $ 451 $ (36 ) $ — $ 438,467 December 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Assets: U.S. government securities $ 205,172 $ 176 $ (20 ) $ 205,328 U.S. corporate bonds 429,148 797 (100 ) 429,845 International corporate bonds 142,568 457 (27 ) 142,998 U.S. commercial paper 52,252 14 (5 ) 52,261 International commercial paper 51,253 5 (2 ) 51,256 $ 880,393 $ 1,449 $ (154 ) $ 881,688

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net consists of the following: December 31, 2020 2019 (in thousands) Computer hardware and software $ 2,758 $ 2,830 Furniture and equipment 1,865 1,828 Leasehold improvements 9,220 8,967 13,843 13,625 Less: Accumulated depreciation (7,088 ) (4,499 ) $ 6,755 $ 9,126
Summary of Accrued Expenses	Accrued expenses consist of the following: December 31, 2020 2019 (in thousands) Accrued research and development costs $ 34,398 $ 46,940 Restructuring 203 - Employee-related 14,566 22,011 Professional services 5,184 16,720 Other 500 947 $ 54,851 $ 86,618

Leases, Commitments and Conti_2

Leases, Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Schedule of Amount of Operating Leases	The following table shows the amounts of operating leases in the balance sheets as of December 31, 2020 and 2019: December 31, Balance sheet location Balance sheet caption 2020 2019 (in thousands) Assets Right-of-use operating asset Right-of-use operating asset $ 25,064 $ 33,771 Liabilities Current operating lease liabilities Operating lease liability, current portion 8,662 10,244 Long-term operating lease liabilities Operating lease liability, net of current portion 19,438 26,848 Total operating lease liabilities $ 28,100 $ 37,092
Schedule of Lease Expense by Lease Type Recognized	Lease expense by lease type recognized during the years ended December 31, 2020 and 2019 was as follows: Year Ended December 31, 2020 2019 (in thousands) Operating lease cost $ 8,838 $ 9,804 Variable lease cost 2,285 2,675 Short-term lease cost 74 438 $ 11,197 $ 12,917
Schedule of Minimum Lease Payments	The minimum lease payments are expected to be as follows: Years Ending December 31, (In thousands) 2021 $ 8,662 2022 8,898 2023 9,105 2024 5,560 2025 - Thereafter - Total lease payments 32,225 Less imputed interest (4,125 ) Present value of operating lease liabilities $ 28,100
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: December 31, 2020 Weighted average remaining lease term in years 3.61 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 consolidated statements of cash flows is as follows: Year Ended December 31, 2020 2019 (in thousands) Cash paid for amounts included in the measurement of lease liabilities $ 9,231 $ 9,946 Right-of-use assets obtained in exchange for lease obligations: Operating leases $ - $ 872 Lease asset de-recognized upon lease cancellation Operating leases $ 2,310 $ -

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Activity Relating to Restricted Stock Units	The table below summarizes activity relating to time-based restricted stock units and performance restricted stock units: Shares Outstanding as of December 31, 2019 333,243 Granted 1,022,276 Vested — Forfeited (397,824 ) Outstanding as of December 31, 2020 957,695
Summary of Activity Relating to Time Based and Performance Based Stock Options	The table below summarizes activity related to time-based and performance-based stock options: Shares Weighted Average Exercise Price Weighted Average Remaining Life (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2019 8,163,113 $ 106.30 7.75 $ 87,972 Granted 1,544,915 56.03 Exercised (118,325 ) 43.34 Forfeited (2,431,873 ) 121.28 Outstanding as of December 31, 2020 7,157,830 $ 91.41 6.91 $ 167,242 Vested and expected to vest as of December 31, 2020 6,469,905 $ 90.94 6.79 $ 153,562 Exercisable as of December 31, 2020 4,674,438 $ 89.51 6.09 $ 120,030
Summary of Stock-Based Compensation Expense Recognized	Stock-based compensation expense recognized during the years ended December 31, 2020, 2019 and 2018 was as follows: Year Ended December 31, 2020 2019 2018 (in thousands) Research and development $ 42,370 $ 62,931 $ 50,871 Selling, general and administrative 51,836 90,300 51,092 Restructuring 1,788 — — $ 95,994 $ 153,231 $ 101,963
Summary of Stock-Based Compensation Expense by Award Type	Stock-based compensation expense recognized during the years ended December 31, 2020, 2019 and 2018 by award type was as follows: Year Ended December 31, 2020 2019 2018 (in thousands) Stock options $ 90,064 $ 140,517 $ 100,342 Restricted stock units 4,904 10,992 651 Employee stock purchase plan 1,026 1,722 970 $ 95,994 $ 153,231 $ 101,963
Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted	The fair value of each option granted under the Company’s equity plans has been calculated on the date of grant using the following weighted average assumptions: Year Ended December 31, 2020 2019 2018 Expected dividend yield 0 % 0 % 0 % Expected volatility 77.86 % 71.34 % 74.45 % Risk-free interest rate 0.97 % 2.21 % 2.68 % Expected term 5.98 years 6.05 years 6.04 years

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Summary of Basic and Diluted Net Income (Loss) Per Share	Basic and diluted net income (loss) per share was calculated as follows for the years ended December 31, 2020, 2019 and 2018: Year Ended December 31, 2020 2019 2018 Basic net income (loss) per share: Numerator: Net income (loss) (in thousands) $ 606,073 $ (680,238 ) $ (372,882 ) Denominator: Weighted average common stock outstanding —basic 51,983,188 50,833,837 46,121,194 Effect of dilutive securities: Stock options 721,791 — — Restricted stock units 292,241 — — ESPP 5,895 — — Total dilutive securities 1,019,927 — — Weighted average common stock outstanding —diluted 53,003,115 50,833,837 46,121,194 Net income (loss) per share—basic $ 11.66 $ (13.38 ) $ (8.08 ) Net income (loss) per share—diluted $ 11.43 $ (13.38 ) $ (8.08 )
Summary of Anti-Dilutive Common Stock Equivalents Outstanding	The following common stock equivalents outstanding as of December 31, 2020, 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: Year Ended December 31, 2020 2019 2018 Stock options 4,781,737 7,677,518 6,758,420 Restricted stock units — — 13,500 Employee stock purchase plan — 33,429 16,398 4,781,737 7,710,947 6,788,318

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Summary of Income (Loss) Before Income Tax Expense	Income (loss) before income tax expense consists of the following: Year Ended December 31, 2020 2019 2018 (in thousands) Domestic $ 639,986 $ (634,289 ) $ (296,040 ) Foreign (33,913 ) (45,949 ) (76,842 ) $ 606,073 $ (680,238 ) $ (372,882 )
Summary of Reconciliation of U.S. Statutory Rate to Company's Effective Tax Rate	A reconciliation of the U.S. statutory rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2020 2019 2018 Tax due at statutory rate 21.0 % 21.0 % 21.0 % State taxes, net of federal 5.7 2.8 6.0 Biogen transaction-related items (10.1 ) — — Stock-based compensation 0.9 1.4 2.5 Foreign rate differential 1.2 (1.6 ) (4.3 ) Federal and state credits (1.5 ) 2.4 2.5 Change in valuation allowance (17.6 ) (25.8 ) (27.6 ) Other 0.4 0.5 (0.1 ) Federal and state rate change — (0.7 ) — 0.0 % 0.0 % 0.0 %
Summary of Significant Components of Company's Net Deferred Tax Asset	Significant components of the Company’s net deferred tax assets at December 31, 2020 and 2019 are as follows: December 31, 2020 2019 (in thousands) Net operating losses $ 222,607 $ 348,848 Capitalized start-up costs 873 982 Tax credit carryforwards 90,460 80,088 Accrued expenses 3,157 4,055 Depreciation and amortization 1,614 2,002 Stock options 56,520 46,750 Right of use asset (5,981 ) (8,059 ) Lease liability 6,705 8,852 Other 148 (246 ) Total net deferred tax asset before valuation allowance 376,103 483,272 Valuation allowance (376,103 ) (483,272 ) Net deferred tax asset $ — $ —

Restructuring (Tables)

Restructuring (Tables)	12 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Summary of Restructuring Activity	Restructuring activity during the year ended December 31, 2020 was as follows: Restructuring accrual (in thousands) Balance as of January 1, 2020 $ - Restructuring expenses incurred 27,743 Cash paid (25,102 ) Non-cash activity (2,438 ) Balance as of December 31, 2020 $ 203

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Financial Information	The following table contains quarterly financial information for 2020 and 2019. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. 2020 First Quarter Second Quarter Third Quarter Fourth Quarter (1) Total (in thousands, except per share amounts) Total revenue $ 2,286 $ 1,089 $ 1,639 $ 1,109,186 $ 1,114,200 Total operating costs and expenses 133,910 140,056 108,797 135,211 517,974 Income (loss) from operations (131,624 ) (138,967 ) (107,158 ) 973,975 596,226 Net income (loss) (126,740 ) (136,347 ) (105,735 ) 974,895 606,073 Net income (loss) per share—basic $ (2.44 ) $ (2.63 ) $ (2.03 ) $ 18.71 $ 11.66 Net income (loss) per share—diluted $ (2.44 ) $ (2.63 ) $ (2.03 ) $ 18.19 $ 11.43 2019 First Quarter Second Quarter Third Quarter Fourth Quarter Total (in thousands, except per share amounts) Total revenue $ 465 $ 873 $ 3,570 $ 1,960 $ 6,868 Total operating costs and expenses 170,317 177,330 190,747 176,598 714,992 Loss from operations (169,852 ) (176,457 ) (187,177 ) (174,638 ) (708,124 ) Net loss (163,406 ) (168,221 ) (179,958 ) (168,653 ) (680,238 ) Net loss per share—basic and diluted $ (3.37 ) $ (3.28 ) $ (3.48 ) $ (3.25 ) $ (13.38 )

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended	129 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Nature Of Business [Line Items]
Accumulated deficit	$ (1,037,494)	$ (1,037,494)	$ (1,643,567)
Net income from up-front	606,100
Up-front payments receive	$ 1,000,000
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		$ 2,800,000

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Intangible assets					$ 0
Lease liabilities		$ 28,100,000	$ 37,092,000
ASC Topic 842 [Member]
Summary Of Significant Accounting Policies [Line Items]
Lease liabilities		$ 28,100,000		$ 44,200,000
Right-of-use assets				$ 41,100,000
Product Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Incremental costs incurred expected amortization period of asset		true
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

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Company's Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	$ 1,661,082	$ 126,705
Total marketable securities	438,467	881,688
Total cash equivalents and marketable securities	2,099,549	1,008,393
Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	1,661,082	126,705
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	1,637,609	65,414
Total cash equivalents and marketable securities	1,637,609	65,414
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	1,637,609	65,414
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	23,473	61,291
Total marketable securities	438,467	881,688
Total cash equivalents and marketable securities	461,940	942,979
Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents	23,473	61,291
U.S. Government Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	160,588	205,328
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	160,588	205,328
U.S. Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	123,107	429,845
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	123,107	429,845
International Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	57,676	142,998
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	57,676	142,998
U.S. Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	45,963	52,261
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	45,963	52,261
International Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total marketable securities	51,133	51,256
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	$ 51,133	$ 51,256

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument Fair Value Carrying Value [Line Items]
Transfers among the Level 1, Level 2 and Level 3 categories	$ 0	$ 0
Marketable securities fair value held to maturity	5,100,000	137,100,000
Impairment of assets	$ 0	$ 0
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	Dec. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 438,052	$ 880,393
Gross Unrealized Gains	451	1,449
Gross Unrealized Losses	(36)	(154)
Fair Value	438,467	881,688
U.S. Government Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	160,589	205,172
Gross Unrealized Gains	11	176
Gross Unrealized Losses	(12)	(20)
Fair Value	160,588	205,328
U.S. Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	122,882	429,148
Gross Unrealized Gains	240	797
Gross Unrealized Losses	(15)	(100)
Fair Value	123,107	429,845
International Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	57,485	142,568
Gross Unrealized Gains	200	457
Gross Unrealized Losses	(9)	(27)
Fair Value	57,676	142,998
U.S. Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	45,963	52,252
Gross Unrealized Gains		14
Gross Unrealized Losses		(5)
Fair Value	45,963	52,261
International Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	51,133	51,253
Gross Unrealized Gains		5
Gross Unrealized Losses		(2)
Fair Value	$ 51,133	$ 51,256

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 13,843	$ 13,625
Less: Accumulated depreciation	(7,088)	(4,499)
Property and equipment, net	6,755	9,126
Computer Hardware and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,758	2,830
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,865	1,828
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 9,220	$ 8,967

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 2,630	$ 2,283	$ 1,143
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	Dec. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Accrued research and development costs	$ 34,398	$ 46,940
Restructuring	203
Employee-related	14,566	22,011
Professional services	5,184	16,720
Other	500	947
Total accrued expenses	$ 54,851	$ 86,618

Leases, Commitments and Conti_3

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

Feb. 28, 2019ft²

Oct. 02, 2018ft²

Sep. 30, 2018ft²

Aug. 01, 2018ft²

Jan. 01, 2018ft²

Mar. 31, 2019ft²

Dec. 31, 2018ft²

Oct. 31, 2018ft²

May 31, 2018ft²

Apr. 30, 2018ft²

Dec. 31, 2020USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2019USD ($)

Jan. 01, 2019USD ($)

Commitments And Contingencies [Line Items]

Lease expire date

Jan. 31, 2022

Operating lease option to extend

true

Operating lease renewal term

5 years

Right-of-use operating asset | $

$ 25,064

$ 33,771

$ 5,300

Lessee, operating lease contract term

3 years

Remaining Amount Of Lease Write Off | $

$ 2,300

Restricted Cash And Cash Equivalents Noncurrent | $

$ 700

Rent expenses | $

$ 6,500

Operating Lease One [Member]

Commitments And Contingencies [Line Items]

Office space rent under operating lease

58,442

54,943

54,943

63,017

58,442

Lease expire date

Aug. 15, 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

19,805

40,419

Lease expire date

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. 29, 2024

Operating lease early effective termination date

Feb. 1, 2021

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

4 years

Leases, Commitments and Conti_4

Leases, Commitments and Contingencies - Schedule of Amounts of Operating Leases (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Assets
Right-of-use operating asset	$ 25,064	$ 33,771	$ 5,300
Liabilities
Current operating lease liabilities	8,662	10,244
Long-term operating lease liabilities	19,438	26,848
Total operating lease liabilities	$ 28,100	$ 37,092

Leases, Commitments and Conti_5

Leases, Commitments and Contingencies - Schedule of Lease Expense by Lease Type Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Operating lease cost	$ 8,838	$ 9,804
Variable lease cost	2,285	2,675
Short-term lease cost	74	438
Total	$ 11,197	$ 12,917

Leases, Commitments and Conti_6

Leases, Commitments and Contingencies - Schedule of Minimum Lease Payments (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Lessee Lease Description [Line Items]
Present value of operating lease liabilities	$ 28,100	$ 37,092
ASU Topic (842) [Member]
Lessee Lease Description [Line Items]
2021	8,662
2022	8,898
2023	9,105
2024	5,560
Total lease payments	32,225
Less imputed interest	(4,125)
Present value of operating lease liabilities	$ 28,100		$ 44,200

Leases, Commitments and Conti_7

Leases, Commitments and Contingencies - Schedule of Weighted Average Remaining Lease Term and Weighted Average Discount Rate of Our Operating Leases (Detail)	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Weighted average remaining lease term in years	3 years 7 months 9 days
Weighted average discount rate	7.50%

Leases, Commitments and Conti_8

Leases, Commitments and Contingencies - Schedule of Supplemental Disclosure of Cash Flow Information Related To Operating Leases (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Cash paid for amounts included in the measurement of lease liabilities	$ 9,231	$ 9,946
Right-of-use assets obtained in exchange for new operating lease liabilities		$ 872
Lease asset de-recognized upon lease cancellation	$ 2,310

Leases, Commitments and Conti_9

Leases, Commitments and Contingencies - CyDex License Agreement - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Commitments And Contingencies [Line Items]
Research and development expense		$ 292,714,000	$ 368,815,000	$ 282,107,000
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
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
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
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
CyDex License Agreement [Member] | Clinical Development [Member] | Brexanolone [Member]
Commitments And Contingencies [Line Items]
Milestone payments		0
CyDex License Agreement [Member] | Clinical Development [Member] | SAGE-689 [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Expected milestone payments		800,000
CyDex License Agreement [Member] | Regulatory Milestones [Member]
Commitments And Contingencies [Line Items]
Construction Expense Related To Milestone Payment		1,300,000
CyDex License Agreement [Member] | Regulatory Milestones [Member] | Brexanolone [Member]
Commitments And Contingencies [Line Items]
Research and development expense related to milestone expense				800,000
Milestone payments				$ 800,000
Intangible asset related to milestone			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
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
Milestone payments related to intangible assets		1,300,000
CyDex License Agreement [Member]
Commitments And Contingencies [Line Items]
Research and development expense		$ 1,300,000

Leases, Commitments and Cont_10

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	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 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	$ 500,000	$ 200,000
Milestone payments			$ 0	500,000	$ 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] | 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
Milestone payments related to intangible assets				$ 500,000

Leases, Commitments and Cont_11

Leases, Commitments and Contingencies - Washington University License Agreement - Additional Information (Detail) - Washington University License Agreement [Member] - USD ($)	1 Months Ended	12 Months Ended
	Nov. 30, 2013	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 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
Milestone payments		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

Collaboration Agreement - Addit

Collaboration Agreement - Additional Information (Detail) - USD ($)

Nov. 30, 2020

Feb. 27, 2019

Jun. 30, 2018

Jun. 12, 2018

Feb. 13, 2018

Dec. 31, 2020

Sep. 30, 2020

Jun. 30, 2020

Mar. 31, 2020

Dec. 31, 2019

Sep. 30, 2019

Jun. 30, 2019

Mar. 31, 2019

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Revenue

$ 1,109,186,000

$ 1,639,000

$ 1,089,000

$ 2,286,000

$ 1,960,000

$ 3,570,000

$ 873,000

$ 465,000

$ 1,114,200,000

$ 6,868,000

$ 90,273,000

Public offering of common stock, net of offering costs, Shares

3,833,334

4,032,012

Shionogi Collaboration Agreement [Member] | SAGE-217 [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration agreement effective date

Jun. 30, 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

Biogen Collaboration Agreement [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaboration agreement effective date

Dec. 28, 2020

Upfront payment

$ 875,000,000

Standalone selling price of license performance obligation

$ 1,100,000,000

1,100,000,000

Revenue

1,100,000,000

Sale of stock, consideration received

$ 1,500,000,000

Public offering of common stock, net of offering costs, Shares

6,241,473

Purchase price

$ 650,000,000

Biogen Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Additional milestone payment receivable

$ 1,600,000,000

Biogen Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member] | Sales Milestones [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Future milestone payments

300,000,000

Biogen Collaboration Agreement [Member] | SAGE-217 [Member] | Maximum [Member] | Regulatory and Commercial Milestones [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Future milestone payments

475,000,000

Biogen Collaboration Agreement [Member] | SAGE-324 [Member] | Maximum [Member] | Sales Milestones [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Future milestone payments

300,000,000

Biogen Collaboration Agreement [Member] | SAGE-324 [Member] | Maximum [Member] | Regulatory and Commercial Milestones [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Future milestone payments

$ 520,000,000

Biogen Stock Purchase Agreement [Member]

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Upfront payment

875,000,000

Purchase price

650,000,000

Transaction price, total

1,100,000,000

1,100,000,000

Premium amount on equity investment

$ 232,500,000

$ 232,500,000

Price per share

$ 104.14

$ 104.14

Premium on per share price

40.00%

Stock issued

$ 417,500,000

Preferred Stock - Additional In

Preferred Stock - Additional Information (Detail) - shares	Dec. 31, 2020	Dec. 31, 2019
Temporary Equity Disclosure [Abstract]
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Common Stock - Additional Infor

Common Stock - Additional Information (Detail) - USD ($)	Dec. 31, 2020	Feb. 27, 2019	Feb. 13, 2018	Dec. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Common stock, shares authorized	120,000,000			120,000,000	120,000,000
Common stock, par value	$ 0.0001			$ 0.0001	$ 0.0001
Dividends declared				$ 0	$ 0
Voting rights				Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders.
Public offering of common stock, net of offering costs, 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		$ 560,900,000	$ 631,200,000
Purchase of treasury stock, Shares				3,033
Total cost of shares held in treasury	$ 400,000			$ 400,000	$ 400,000
Private Placement [Member] | Biogen
Class Of Stock [Line Items]
Public offering of common stock, net of offering costs, Shares	6,241,473
Common stock price per share	$ 104.14			$ 104.14
Stock Issued During Period Value New Issues	$ 650,000,000

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail)	Jan. 01, 2020shares	Dec. 31, 2020USD ($)Milestone$ / sharesshares	Dec. 31, 2019USD ($)Milestone$ / sharesshares	Dec. 31, 2018USD ($)Milestone$ / sharesshares	Dec. 31, 2017shares	Dec. 31, 2016	Dec. 31, 2015	Sep. 20, 2018shares	Jul. 02, 2014shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation granted under plan vested period		4 years
Share based compensation, vest period		1 year
Share based compensation, term of plan		10 years
Total number of shares reserved | shares		12,535,574
Common stock available for issuance under stock option plan | shares		4,420,049
Restricted stock units granted | shares		550,890	0	0
Stock-based compensation expense		$ 95,994,000	$ 153,231,000	$ 101,963,000
Stock-based compensation expense		$ 95,994,000	$ 153,231,000	$ 101,963,000
Weighted average grant date fair value per share | $ / shares		$ 37.53	$ 82.39	$ 109.92
Share option, weighted-average forfeiture rates		20.60%	13.70%	10.70%
Non-employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, term of plan				10 years
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation granted under plan vested period					2 years
Restricted stock units granted | shares		1,022,276			32,500
Fair value of restricted stock units vested		$ 0	$ 2,000,000	$ 2,600,000
Outstanding and unvested performance restricted stock units | shares		957,695	333,243
Stock-based compensation expense		$ 4,904,000	$ 10,992,000	651,000
Stock-based compensation expense		$ 4,904,000	$ 10,992,000	$ 651,000
Performance Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted | shares		471,386	393,539	71,400
Fair value of restricted stock units vested		$ 0	$ 11,100,000	$ 0
Percentage Of Milestone Achieved		18.00%
Outstanding and unvested performance restricted stock units | shares		957,695
Total unrecognized stock-based compensation expense		$ 58,200,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted | shares		1,544,915
Total number of shares reserved | shares		7,157,830	8,163,113
Total unrecognized stock-based compensation expense		$ 120,500,000
Weighted average period of unrecognized compensation costs		1 year 9 months 3 days
Intrinsic value of options exercised		$ 2,100,000	$ 119,100,000	98,300,000
Stock-based compensation expense		90,064,000	140,517,000	100,342,000
Stock-based compensation expense		$ 90,064,000	$ 140,517,000	$ 100,342,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted | shares		0	0	524,003
Total unrecognized stock-based compensation expense		$ 20,600,000
Number of shares outstanding and unvested stock options | shares		288,575
Performance-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 0	$ 0	$ 0
Stock-based compensation expense		$ 0	$ 0	0
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
Stock-based compensation expense				$ 6,900,000
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		25.00%
Restricted Stock Units Vest One Year Anniversary [Member] | Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units cliff vesting percentage		25.00%			50.00%
Restricted stock units vesting period month and year		2021-04			2018-02
Restricted Stock Units Vest Two Year Anniversary [Member] | Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units cliff vesting percentage		75.00%			50.00%
Restricted stock units vesting period month and year		2022-04			2019-02
2011 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted | shares		0
2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares annual increase added to plan | shares	2,075,087
Stock-based compensation expense		$ 0
Milestones achieved | Milestone		0	1	1
Stock-based compensation expense		$ 0
2014 Plan [Member] | Milestone Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of performance based grants that were achieved					33.00%	50.00%	35.00%
2014 Plan [Member] | Milestone Four [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of performance based grants that were achieved				20.00%	33.00%
2014 Plan [Member] | Milestone Five [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of performance based grants that were achieved				19.00%
2014 Plan [Member] | Consultant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense				$ 0
Stock-based compensation expense				0
2014 Plan [Member] | Performance Milestone [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 16,300,000	4,400,000
Milestones achieved | Milestone		1
Stock-based compensation expense			$ 16,300,000	$ 4,400,000
2014 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 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares reserved for issuance | shares								1,200,000
Shares of common stock initially authorized for issuance under this plan | shares								1,200,000
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of shares reserved for issuance | shares									282,000
Shares of common stock initially authorized for issuance under this plan | shares									282,000
Number of shares issued under the plan | shares		177,879
Accrued expenses		$ 300,000
Total number of shares available for issuance | shares		104,121

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Activity Relating to Restricted Stock Units (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Shares	550,890	0	0
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, Shares at beginning balance	333,243
Granted, Shares	1,022,276			32,500
Forfeited, Shares	(397,824)
Outstanding, Shares at ending balance	957,695	333,243

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Activity Relating to Time Based and Performance Based Stock Options (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Ending balance, Outstanding Shares	12,535,574
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Outstanding Shares	8,163,113
Granted, Shares	1,544,915
Exercised, Shares	(118,325)
Forfeited, Shares	(2,431,873)
Ending balance, Outstanding Shares	7,157,830	8,163,113
Vested and expected to vest, Shares	6,469,905
Exercisable, Shares	4,674,438
Beginning balance, Outstanding Weighted Average Exercise Price	$ 106.30
Granted, Weighted Average Exercise Price	56.03
Exercised, Weighted Average Exercise Price	43.34
Forfeited, Weighted Average Exercise Price	121.28
Ending balance, Outstanding Weighted Average Exercise Price	91.41	$ 106.30
Vested and expected to vest, Weighted Average Exercise Price	90.94
Exercisable, Weighted Average Exercise Price	$ 89.51
Outstanding, Weighted Average Remaining Life	6 years 10 months 28 days	7 years 9 months
Vested and expected to vest, Weighted Average Remaining Life	6 years 9 months 14 days
Exercisable, Weighted Average Remaining Life	6 years 1 month 2 days
Outstanding, Aggregate Intrinsic Value	$ 167,242	$ 87,972
Vested and expected to vest, Aggregate Intrinsic Value	153,562
Exercisable, Aggregate Intrinsic Value	$ 120,030

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 95,994	$ 153,231	$ 101,963
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	42,370	62,931	50,871
Selling, General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	51,836	$ 90,300	$ 51,092
Restructuring Charges [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,788

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of Stock-Based Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 95,994	$ 153,231	$ 101,963
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	90,064	140,517	100,342
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	4,904	10,992	651
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,026	$ 1,722	$ 970

Stock-Based Compensation - Su_5

Stock-Based Compensation - Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility	77.86%	71.34%	74.45%
Risk-free interest rate	0.97%	2.21%	2.68%
Expected term	5 years 11 months 23 days	6 years 18 days	6 years 14 days

Net Income (Loss) Per Share - S

Net Income (Loss) Per Share - Summary of Basic and Diluted Net Income (Loss) Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income (loss)	$ 974,895	$ (105,735)	$ (136,347)	$ (126,740)	$ (168,653)	$ (179,958)	$ (168,221)	$ (163,406)	$ 606,073	$ (680,238)	$ (372,882)
Denominator:
Weighted average number of common shares outstanding—basic									51,983,188	50,833,837	46,121,194
Effect of dilutive securities:
Dilutive effect of shares of common stock equivalents									1,019,927	0	0
Weighted average common stock outstanding —diluted									53,003,115	50,833,837	46,121,194
Net income (loss) per share—basic	$ 18.71	$ (2.03)	$ (2.63)	$ (2.44)					$ 11.66	$ (13.38)	$ (8.08)
Net income (loss) per share—diluted	$ 18.19	$ (2.03)	$ (2.63)	$ (2.44)					$ 11.43	$ (13.38)	$ (8.08)
Stock Options [Member]
Effect of dilutive securities:
Dilutive effect of shares of common stock equivalents									721,791	0	0
Restricted Stock Units [Member]
Effect of dilutive securities:
Dilutive effect of shares of common stock equivalents									292,241	0	0
Employee Stock Purchase Plan [Member]
Effect of dilutive securities:
Dilutive effect of shares of common stock equivalents									5,895	0	0

Net Income (Loss) Per Share -_2

Net Income (Loss) Per Share - Summary of Anti-Dilutive Common Stock Equivalents Outstanding (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	4,781,737	7,710,947	6,788,318
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents	4,781,737	7,677,518	6,758,420
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents			13,500
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive common stock equivalents		33,429	16,398

Income Taxes - Summary of Incom

Income Taxes - Summary of Income (Loss) Before Income Tax Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Domestic	$ 639,986	$ (634,289)	$ (296,040)
Foreign	(33,913)	(45,949)	(76,842)
Net income (loss) before income tax expense	$ 606,073	$ (680,238)	$ (372,882)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Current tax expense	$ 0
Deferred tax expense	0
Federal operating loss carryforwards	41,700,000
State operating loss carryforwards	$ 438,400,000
Federal net operating loss carryforwards expiration year	2033
State net operating loss carryforwards expiration year	2033
Federal orphan drug tax credit carry forwards	$ 42,300,000
Tax credit carry forwards expiration period	2034
Change in amount of deferred tax assets	$ (107,200,000)
Valuation allowance	376,103,000	$ 483,272,000
Valuation allowance, increase (decrease), amount	(107,200,000)	174,900,000	$ 102,900,000
Unrecognized tax benefits	0	0	$ 0
Accrued interest or penalties related to uncertain tax positions	0	$ 0
Uncertain tax positions	0
Domestic Tax Authority [Member]
Income Tax Disclosure [Line Items]
Additional federal net operating loss carryforwards that do not expire	886,100,000
Research and development tax credits carryforwards	$ 40,700,000
Research and development tax credits carryforwards expiration year	2031
State and Local Jurisdiction [Member]
Income Tax Disclosure [Line Items]
Research and development tax credits carryforwards	$ 9,400,000
Research and development tax credits carryforwards expiration year	2031

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of U.S. Statutory Rate to Company's Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Tax due at statutory rate	21.00%	21.00%	21.00%
State taxes, net of federal	5.70%	2.80%	6.00%
Biogen transaction-related items	(10.10%)
Stock-based compensation	0.90%	1.40%	2.50%
Foreign rate differential	1.20%	(1.60%)	(4.30%)
Federal and state credits	(1.50%)	2.40%	2.50%
Change in valuation allowance	(17.60%)	(25.80%)	(27.60%)
Other	0.40%	0.50%	(0.10%)
Federal and state rate change		(0.70%)
Total effective tax rate	0.00%	0.00%	0.00%

Income Taxes - Summary of Signi

Income Taxes - Summary of Significant Components of Company's Net Deferred Tax Asset (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Net operating losses	$ 222,607	$ 348,848
Capitalized start-up costs	873	982
Tax credit carryforwards	90,460	80,088
Accrued expenses	3,157	4,055
Depreciation and amortization	1,614	2,002
Stock options	56,520	46,750
Right of use asset	(5,981)	(8,059)
Lease liability	6,705	8,852
Other	148	(246)
Total net deferred tax asset before valuation allowance	376,103	483,272
Valuation allowance	$ (376,103)	$ (483,272)

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Postemployment Benefits [Abstract]
Employer matching contribution, percent of match	50.00%	50.00%	50.00%
Maximum annual contributions per employee, percent	6.00%	6.00%	6.00%
Employer contribution	$ 2.2	$ 3.6	$ 1.8
Defined Contribution Plan, Sponsor Location [Extensible List]	country:US	country:US	country:US
Defined Contribution Plan, Tax Status [Extensible List]	us-gaap:QualifiedPlanMember	us-gaap:QualifiedPlanMember	us-gaap:QualifiedPlanMember

Restructuring - Additional Info

Restructuring - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2020	Dec. 31, 2020
Restructuring Cost And Reserve [Line Items]
Operating expenses, workforce reduction, percent	53.00%
Employee Severance
Restructuring Cost And Reserve [Line Items]
Employee severance, benefits, and related costs		$ 27.7

Restructuring - Summary of Rest

Restructuring - Summary of Restructuring Activity (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Restructuring And Related Activities [Abstract]
Restructuring	$ 27,743
Cash paid	(25,102)
Non-cash activity	(2,438)
Balance	$ 203

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 1,109,186	$ 1,639	$ 1,089	$ 2,286	$ 1,960	$ 3,570	$ 873	$ 465	$ 1,114,200	$ 6,868	$ 90,273
Total operating costs and expenses	135,211	108,797	140,056	133,910	176,598	190,747	177,330	170,317	517,974	714,992	483,511
Income (loss) from operations	973,975	(107,158)	(138,967)	(131,624)	(174,638)	(187,177)	(176,457)	(169,852)	596,226	(708,124)	(393,238)
Net income (loss)	$ 974,895	$ (105,735)	$ (136,347)	$ (126,740)	$ (168,653)	$ (179,958)	$ (168,221)	$ (163,406)	$ 606,073	$ (680,238)	$ (372,882)
Net income (loss) per share—basic	$ 18.71	$ (2.03)	$ (2.63)	$ (2.44)					$ 11.66	$ (13.38)	$ (8.08)
Net income (loss) per share—diluted	$ 18.19	$ (2.03)	$ (2.63)	$ (2.44)					$ 11.43	(13.38)	$ (8.08)
Net loss per share—basic and diluted					$ (3.25)	$ (3.48)	$ (3.28)	$ (3.37)		$ (13.38)

Selected Quarterly Financial _4

Selected Quarterly Financial Data (Unaudited) - Additional Information (Detail) $ in Billions	12 Months Ended
	Dec. 31, 2020USD ($)
Biogen Collaboration Agreement [Member]
Collaboration revenue	$ 1.1