Aimmune Therapeutics (AIMT) 10-K 27 Feb 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 14, 2020	Jun. 30, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Trading Symbol	AIMT
Entity Registrant Name	AIMMUNE THERAPEUTICS, INC.
Entity Central Index Key	0001631650
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		65,041,825
Entity Public Float			$ 919,670,159
Entity Interactive Data Current	Yes
Entity File Number	001-37519
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	45-2748244
Entity Address Address Line1	8000 Marina Blvd
Entity Address Address Line2	Suite #300
Entity Address, City or Town	Brisbane
Entity Address, State or Province	CA
Entity Address Postal Zip Code	94005
City Area Code	650
Local Phone Number	614-5220
Document Annual Report	true
Document Transition Report	false
Title of each class	Common Stock, par value $0.0001 per share
Name of exchange on which registered	NASDAQ
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement relating to the 2020 Annual Meeting of Shareholders, scheduled to be held on May 27, 2020, are incorporated by reference into Part III of this Annual Report on Form 10-K to the extent stated herein. The Definitive Proxy Statement will be filed within 120 days of the Registrant’s fiscal year ended December 31, 2019.

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 79,880	$ 107,511
Short-term investments	63,633	196,421
Prepaid expenses and other current assets	5,564	8,687
Total current assets	149,077	312,619
Long-term investments	14,661
Property and equipment, net	28,604	26,328
Operating lease right-of-use-assets	11,512
Prepaid expenses and other assets	515	608
Total assets	204,369	339,555
Current liabilities:
Accounts payable	13,882	8,833
Accrued liabilities	31,286	29,144
Operating lease liabilities, current	2,257
Other current liabilities	23	35
Total current liabilities	47,448	38,012
Long-term debt, net of discount	41,028
Operating lease liabilities	10,524
Other liabilities	1,345	2,596
Total liabilities	100,345	40,608
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock, par value $0.0001 per share - 10,000 shares authorized at December 31, 2019 and 2018; 0 shares issued and outstanding at December 31, 2019 and 2018
Common stock, par value $0.0001 per share - 290,000 shares authorized as of December 31, 2019 and 2018; 63,779 and 62,142 shares issued and outstanding as of December 31, 2019 and 2018, respectively	6	6
Additional paid-in capital	828,618	775,283
Accumulated other comprehensive income (loss)	80	(108)
Accumulated deficit	(724,680)	(476,234)
Total stockholders’ equity	104,024	298,947
Total liabilities and stockholders’ equity	$ 204,369	$ 339,555

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	290,000,000	290,000,000
Common stock, shares issued	63,779,000	62,142,000
Common stock, shares outstanding	63,779,000	62,142,000

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses
Research and development	$ 123,987	$ 133,420	$ 89,325
General and administrative	125,817	81,921	43,949
Total operating expenses	249,804	215,341	133,274
Loss from operations	(249,804)	(215,341)	(133,274)
Interest income	5,851	4,984	2,190
Interest expense	(4,916)	(113)	(114)
Other income (expense), net	1,088	(221)	(71)
Loss before provision for income taxes	(247,781)	(210,691)	(131,269)
Provision for income taxes	716	61	56
Net loss	(248,497)	(210,752)	(131,325)
Other comprehensive loss, net of tax:
Unrealized gain (loss) on investments	188		(81)
Comprehensive loss	$ (248,309)	$ (210,752)	$ (131,406)
Net loss per share, basic and diluted	$ (3.97)	$ (3.67)	$ (2.61)
Weighted average shares used in computing net loss per common share, basic and diluted	62,558	57,403	50,401

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2016	$ 285,972	$ 5	$ 420,151	$ (27)	$ (134,157)
Beginning balances (in shares) at Dec. 31, 2016		50,204
Issuance of common stock upon exercise of vested options and vesting of restricted stock units	6,520		6,520
Issuance of common stock upon exercise of vested options and vesting of restricted stock units (in shares)		887
Stock-based compensation	16,719		16,719
Other comprehensive income (loss)	(81)			(81)
Net loss	(131,325)				(131,325)
Ending balances at Dec. 31, 2017	177,805	$ 5	443,390	(108)	(265,482)
Ending balances (in shares) at Dec. 31, 2017		51,091
Issuance of common stock upon exercise of vested options and vesting of restricted stock units	10,726		10,726
Issuance of common stock upon exercise of vested options and vesting of restricted stock units (in shares)		1,188
Issuance of common stock upon public offering	190,436	$ 1	190,435
Issuance of common stock upon public offering (in shares)		6,325
Issuance of common stock upon securities purchase agreement	98,000		98,000
Issuance of common stock upon securities purchase agreement (in shares)		3,538
Stock-based compensation	32,732		32,732
Net loss	(210,752)				(210,752)
Ending balances at Dec. 31, 2018	298,947	$ 6	775,283	(108)	(476,234)
Ending balances (in shares) at Dec. 31, 2018		62,142
Issuance of common stock upon exercise of vested options and vesting of restricted stock units	20,406		20,406
Issuance of common stock upon exercise of vested options and vesting of restricted stock units (in shares)		1,637
Stock-based compensation	32,929		32,929
Other comprehensive income (loss)	188			188
Accumulated depreciation upon adoption of ASU Topic 842	51				51
Net loss	(248,497)				(248,497)
Ending balances at Dec. 31, 2019	$ 104,024	$ 6	$ 828,618	$ 80	$ (724,680)
Ending balances (in shares) at Dec. 31, 2019		63,779

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (248,497)	$ (210,752)	$ (131,325)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation expense	4,086	1,598	966
Stock-based compensation expense	32,929	32,732	16,719
Non-cash interest expense	4,626
Amortization of premium on investment securities	(1,631)	(886)	511
Changes in operating assets and liabilities:
Prepaid expenses and other assets	3,888	(1,995)	(1,435)
Accounts payable	6,200	2,688	2,315
Accrued liabilities	2,039	7,412	11,557
Other liabilities	952	75	1,087
Net cash used in operating activities	(195,408)	(169,128)	(99,605)
Cash flows from investing activities:
Purchase of property and equipment	(8,047)	(9,420)	(6,425)
Purchase of investments	(166,321)	(261,293)	(129,534)
Maturities of investments	286,267	174,703	178,521
Net cash provided by (used in) investing activities	111,899	(96,010)	42,562
Cash flows from financing activities:
Borrowings under debt agreement	40,000
Debt issuance costs	(3,856)
Proceeds from underwritten public offering, net of offering costs		288,435	6,520
Net cash proceeds from exercise of stock options, including early exercise	20,406	10,727
Tax withholdings related to net share settlements of restricted stock units	(672)
Net cash provided by financing activities	55,878	299,162	6,520
Net (decrease) increase in cash and cash equivalents	(27,631)	34,024	(50,523)
Cash and cash equivalents at the beginning of the year	107,511	73,487	124,010
Cash and cash equivalents at the end of the year	79,880	107,511	73,487
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment purchases included in accounts payable and accrued liabilities	$ 1,048	1,301	1,355
Supplemental cash flow disclosures:
Cash paid for taxes		$ 148	$ 39

Formation and Business of the C

Formation and Business of the Company	12 Months Ended
	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Formation and Business of the Company	1. Formation and Business of the Company Aimmune Therapeutics, Inc., or the Company, is a biopharmaceutical company focused on developing and commercializing new therapeutic approaches, including the development of proprietary product candidates, for the treatment of peanut and other food allergies. We are headquartered in Brisbane, California, and were incorporated in the state of Delaware on June 24, 2011. Our main therapeutic approach, which we refer to as C O D I T TM PALFORZIA TM Since inception, we have incurred net losses and negative cash flows from operations. During the year ended December 31, 2019, we incurred a net loss of $248.5 million and used $195.4 million of cash in operations. As of December 31, 2019, we had an accumulated deficit of $724.7 million and we do not expect to experience positive cash flows in the near future. As of December 31, 2019, we had cash, cash equivalents and investments of $158.2 million. With the proceeds from Nestlé Health Science’s $200.0 million equity investment and the draw of the second loan tranche from KKR of $85.0 million in February 2020, we anticipate that these financial resources will fully fund us based on our current business plan. We have financed our operations to date primarily through private placements of our equity securities, our initial public offering, or IPO, of common stock in August 2015, an underwritten public offering of common stock in February and March 2018 and our loan agreement entered into in January 2019. Our ability to continue to meet our obligations and to achieve our business objectives is dependent upon a number of factors, which include commercializing PALFORZIA, obtaining European Medicines Agency, or EMA, approval of our Marketing Authorization Application for PALFORZIA, raising additional capital, the successful and timely completion of our clinical trials, our ability to control expenses and generating sufficient revenue in the United States and Europe. Failure to generate sufficient revenue in the United States, manage discretionary expenditures, or raise additional financing, as required, may adversely impact our ability to achieve our intended business objectives.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Preparation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States, or U.S. GAAP, and include the accounts of our wholly-owned subsidiaries. All significant intercompany transactions have been eliminated. We operate in one reportable segment. Foreign Currency Translation Our functional currency and the functional currency of all of our subsidiaries is the United States dollar. Accordingly, monetary assets and liabilities in the non-functional currency of these subsidiaries are remeasured using exchange rates in effect at the end of the period. Costs in local currency are remeasured using average exchange rates for the period, except for costs related to those balance sheet items that are remeasured using historical exchange rates. The resulting remeasurement gains and losses are included in the consolidated statements of operations and comprehensive loss as incurred and have not been material for all periods presented. Use of Estimates The preparation of the accompanying consolidated financial statements in accordance with U.S. GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of costs and expenses during the reporting period. We base our estimates and assumptions on historical experience when available and on various factors that we believe to be reasonable under the circumstances. We evaluate our estimates and assumptions on an ongoing basis. Our actual results could differ from these estimates under different assumptions or conditions. Cash and Cash Equivalents We consider all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents, which are carried at estimated fair value, consist primarily of money market funds and certain available-for-sale investments with maturities of three months or less. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. We operate in one reportable segment. Concentration of Credit Risk Financial instruments that potentially subject us to a concentration of credit risk consist of cash and cash equivalents and certain investments in money market funds, agency securities, corporate securities, U.S. government securities and commercial paper. Bank deposits are primarily held by a single financial institution and these deposits may exceed insured limits. We are exposed to credit risk in the event of default by the financial institution holding our cash and cash equivalents and issuers of investments that are recorded on our consolidated balance sheets. We mitigate our risk by investing in high-grade instruments and limiting the concentration in any one issuer, which limits our exposure. Investments Our investments consist of available-for-sale securities. Investments with original maturities of greater than 90 days but less than one (1) year are classified as short-term on the consolidated balance sheets. Investments with original maturities greater than one (1) year are classified as long-term on the consolidated balance sheets. Our investments in available-for-sale securities are reported at estimated fair value. Available-for-sale securities consist primarily of agency securities, corporate securities, U.S. government securities and commercial paper. Unrealized gains and losses related to changes in the fair value of securities are recognized in accumulated other comprehensive income or loss, net of tax, on our consolidated balance sheets. Changes in the fair value of available-for-sale securities impact the consolidated statements of operations and comprehensive loss only when such securities are sold or an other-than-temporary impairment is recognized. Realized gains and losses on the sale of securities are determined by specific identification of each security’s cost basis. We regularly review our investment portfolio to determine if any security is other-than-temporarily impaired, which would require us to record an impairment charge in the period any such determination is made. We consider factors such as the duration, severity and the reason for the decline in value, the financial condition of the issuer and any changes thereto, the potential recovery period and our intent to sell. For debt securities, we also consider whether (i) it is more likely than not that we will be required to sell the debt securities before recovery of their amortized cost basis, and (ii) the amortized cost basis cannot be recovered as a result of credit losses. Our assessment on whether a security is other-than-temporarily impaired could change in the future due to new developments or changes in assumptions related to any particular security. Property and Equipment Property and equipment are stated at cost, less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets. Maintenance and repairs are charged to the consolidated statements of operations and comprehensive loss as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss, if any, is reflected in the consolidated statements of operations and comprehensive loss. The useful lives of property and equipment are as follows: Computer equipment 3 years Furniture and office equipment 4 years Manufacturing equipment 7 years Buildings 25 years Leasehold improvements Shorter of remaining lease terms or useful life Impairment of Long-Lived Assets We evaluate our long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows expected to result from the use of the asset and its eventual disposition. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired assets. We have not recorded impairment of any long-lived assets in the periods presented. Leases Leases are classified as either finance or operating leases based on the principle of whether or not the lease is effectively a finance purchase by us. Lease expense is recognized over the term of the lease based on an effective interest method for finance leases and on a straight-line basis for operating leases. We also record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Research and Development We expense research and development costs as incurred. We record accrued liabilities for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of pre-clinical studies and clinical trials, contract manufacturing activities and pre-approval inventory. These costs are a significant component of our research and development expenses. We accrue for these costs based on factors such as estimates of the work completed and in accordance with agreements established with our third-party service providers under the service agreements. We make significant judgments and estimates in determining the accrued liabilities balance in each reporting period. As actual costs become known, we adjust our accrued liabilities. We have not experienced any material differences between accrued costs and actual costs incurred. However, the status and timing of actual services performed, number of patients enrolled and the rate of patient enrollments may vary from our estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to our accruals could materially affect our results of operations. Stock-Based Compensation We recognize compensation costs related to stock options granted to employees and directors based on the estimated fair value of the awards on the date of grant, net of estimated forfeitures. We estimate the grant date fair value using the Black-Scholes option-pricing model. The grant date fair value of the stock-based awards is generally recognized on a straight-line basis over the requisite service period, which is generally the vesting period of the respective awards. The fair value of the shares granted pursuant to the 2015 Employee Stock Purchase Plan, or the 2015 ESPP, In determining the fair value of the stock-based awards used to calculate stock-based compensation expense, we use the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires judgment to determine. • Expected Term. The expected term of stock-based awards represents the weighted average period the stock-based awards are expected to be outstanding. We have opted to use the simplified method for estimating the expected term as provided by the Securities and Exchange Commission Staff Accounting Bulletin, or SAB, 110 as our stock-based awards are considered “plain vanilla”. The simplified method calculates the expected term as the average time-to-vesting and the contractual life of the options. We plan to continue to use the simplified method under SAB 110 until we have sufficient exercise history as a publicly traded company. • Expected Volatility. As we have limited trading history for our common stock, the expected stock price volatility assumption is determined based on the historical volatilities of a group of industry peers as well as the historical volatility of our own common stock since we began trading subsequent to our IPO in August 2015. Industry peers consist of several public companies in the biopharmaceutical industry with comparable characteristics including enterprise value, risk profiles and position within the industry. We intend to continue to consistently apply this process using the same or similar public companies until a sufficient amount of historical information regarding the volatility of our own common stock share price becomes available, or unless circumstances change such that the identified companies are no longer similar to us, in which case, more suitable companies whose share prices are publicly available would be utilized in the calculation. • Risk-Free Interest Rate. The risk-free interest rate is based on the implied yield available on U.S. Treasury zero-coupon issues in effect at the time of grant for periods corresponding with the expected term of the stock-based award. • Expected Dividend Yield. We have never paid dividends on our common stock and have no plans to pay dividends on our common stock. Therefore, we used an expected dividend yield of zero for all years presented. Restricted Stock Units, or RSUs, are measured based on the fair market value of the underlying stock on the date of grant and recognized as expense on a straight-line basis over the employee’s requisite service period (generally the vesting period). In addition to the Black-Scholes assumptions, we estimate our forfeiture rate based on an analysis of our actual forfeitures and will continue to evaluate the adequacy of the forfeiture rate based on actual forfeiture experience, analysis of employee turnover behavior and other factors. The impact from any forfeiture rate adjustment would be recognized in full in the period of adjustment, and if the actual number of future forfeitures differs from our estimates, we might be required to record adjustments to stock-based compensation in future periods. We will continue to use judgment in evaluating the expected volatility, expected terms and forfeiture rates utilized for our stock-based compensation expense calculations on a prospective basis. Income Taxes We use the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of reported assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. We must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to our lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. Tax benefits from uncertain tax positions are recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on technical merits. The amount recognized is measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon effective settlement. Comprehensive Income or Loss Comprehensive income or loss is defined as the change in equity during a period from transactions and other events, excluding changes resulting from investments from owners and distributions to owners. Other comprehensive loss includes net loss and unrealized gains and losses on available-for-sale investments. Net Loss per Share The following common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because their inclusion would have been antidilutive : Year Ended December 31, 2019 2018 2017 Stock options 7,629,823 7,133,113 6,629,111 Restricted stock units 530,795 309,847 16,638 Fair Value Measurements We define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Our valuation techniques are based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect our market assumptions. We classify these inputs into the following hierarchy: Level 1 —Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2 —Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities 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 related assets or liabilities; and Level 3 —Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. Financial instruments include cash equivalents, investments, accounts payable, and accrued liabilities. Our cash equivalents and investments are carried at estimated fair value and remeasured on a recurring basis. The carrying value of accounts payable and accrued liabilities approximate their estimated fair value due to the relatively short-term nature of these instruments. Our valuation techniques used to measure the fair value of money market funds were derived from quoted prices in active markets for identical assets. The valuation techniques used to measure the fair value of investments, all of which have counterparties with high credit ratings, were valued based on quoted market prices or model-driven valuations using significant inputs derived from or corroborated by observable market data. In accordance with fair value accounting requirements, companies may choose to measure eligible financial instruments and certain other items at fair value. We have not elected the fair value option for any eligible financial instruments. Recently Adopted Accounting Pronouncements We adopted Accounting Standards Update, or ASU No. 2016-02, Leases (Topic 842) Lease (Topic 841): Targeted Improvements We adopted ASU No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting (Topic 718) We adopted ASU No. 2019-12, Simplifying the Accounting for Income Taxes Recently Issued Accounting Pronouncements Not Yet Adopted In August 2018, the Financial Accounting Standards Board, or FASB, issued ASU 2018-13, Fair Value Measurement: Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement unobservable inputs used to develop Level 3 fair value measurements, and related changes in unrealized gains and losses included in other comprehensive income. ASU 2018-13 is effective for fiscal periods beginning after December 15, 2019, with early adoption permitted. We a dopt ed this guidance on January 1, 2020 . T he adoption of ASU 2018-13 will not have a material impact on the disclosures in our consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

Available-for-Sale Securities a

Available-for-Sale Securities and Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Available-for-Sale Securities and Fair Value Measurements	3. Available-for-Sale Securities and Fair Value Measurements The following tables set forth our financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands ): December 31, 2019 Level 1 Level 2 Level 3 Total Cash and cash equivalents: Cash and money market funds $ 79,880 $ — $ — $ 79,880 Total cash and cash equivalents $ 79,880 $ — $ — $ 79,880 Investments: Agency securities — 8,862 — 8,862 Corporate securities — 30,338 — 30,338 Commercial paper — 7,949 — 7,949 U.S. government securities — 31,145 — 31,145 Total investments $ — $ 78,294 $ — $ 78,294 December 31, 2018 Level 1 Level 2 Level 3 Total Cash and cash equivalents: Cash and money market funds $ 107,511 $ — $ — $ 107,511 Total cash and cash equivalents $ 107,511 $ — $ — $ 107,511 Investments: Agency securities — 17,352 — 17,352 Corporate securities — 54,474 — 54,474 Commercial paper — 5,965 — 5,965 U.S. government securities — 118,630 — 118,630 Total investments $ — $ 196,421 $ — $ 196,421 Our valuation techniques used to measure the fair value of money market funds were derived from quoted prices in active markets for identical assets. The valuation techniques used to measure the fair value of investments, all of which have counterparties with high credit ratings, were valued based on quoted market prices or model-driven valuations using significant inputs derived from or corroborated by observable market data. Investments are carried at fair value. During the years ended December 31, 2019 and 2018, there were no transfers between Level 1 and Level 2 of the fair value hierarchy. Available-for-sale investments are carried at fair value and are included in the tables above. The aggregate market value, cost basis, and gross unrealized gains and losses of available-for-sale investments by security type, classified in cash equivalents and investments, as of December 31, 2019 and 2018 are as follows (in thousands): December 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Total Fair Value Agency securities $ 8,856 $ 6 $ — $ 8,862 Corporate securities 30,286 55 (3 ) 30,338 Commercial paper 7,949 — — 7,949 U.S. government securities 31,123 22 — 31,145 Total available-for-sale investments $ 78,214 $ 83 $ (3 ) $ 78,294 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Total Fair Value Agency securities $ 17,361 $ — $ (9 ) $ 17,352 Corporate securities 54,536 — (62 ) 54,474 Commercial paper 5,965 — — 5,965 U.S. government securities 118,667 14 (51 ) 118,630 Total available-for-sale investments $ 196,529 $ 14 $ (122 ) $ 196,421 At December 31, 2019, all of the available-for-sale securities have contractual maturities within two years. We periodically review our available-for-sale investments for other-than-temporary impairment loss. We consider factors such as the duration, severity and the reason for the decline in value, the potential recovery period and our intent to sell. For debt securities, we also consider whether (i) it is more likely than not that we will be required to sell the debt securities before recovery of their amortized cost basis, and (ii) the amortized cost basis cannot be recovered as a result of credit losses. During the years ended December 31, 2019, 2018, and 2017 we did not recognize any other-than-temporary impairment losses. All marketable securities with unrealized losses have been in a loss position for less than twelve months. The carrying value of our long-term debt approximates its fair value at each balance sheet date due to its variable interest rate, which approximates a market interest rate.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	4. Balance Sheet Components Property and Equipment, Net Property and equipment, net consists of the following (in thousands): Year Ended December 31, 2019 2018 Furniture and equipment $ 2,660 $ 2,221 Computer equipment 2,820 2,073 Manufacturing equipment 9,012 1,733 Leased equipment 100 100 Leasehold improvements 14,525 4,469 Buildings — 688 Construction in progress 6,649 18,295 Property and equipment, gross 35,766 29,579 Less: accumulated depreciation (7,162 ) (3,251 ) Property and equipment, net $ 28,604 $ 26,328 Depreciation expense for the years ended December 31, 2019, 2018 and 2017 was $4.1 million, $1.6 million and $1.0 million, respectively. Accrued Liabilities Accrued liabilities consist of the following (in thousands ): Year Ended December 31, 2019 2018 Compensation and benefits $ 13,286 $ 8,912 Research and development 11,336 15,504 Professional and consulting 6,627 4,691 Other 37 37 Total accrued liabilities $ 31,286 $ 29,144

Long-Term Debt, Net of Discount

Long-Term Debt, Net of Discounts	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Long-Term Debt, Net of Discounts	5. Long-Term Debt, Net of Discounts In January 2019, we entered into a loan agreement with an affiliate of KKR for up to $170.0 million in three tranches, or the KKR Loans. Of the total loan amount, $40.0 million was funded upon the closing of the transaction in January 2019 and $85.0 million was funded in February 2020 following FDA approval of PALFORZIA and satisfaction of other customary borrowing conditions. The remaining $45.0 million is to be made available at our option in 2020, upon the satisfaction of certain borrowing conditions, including our achievement of aggregate net sales (as defined in the agreement) for PALFORIZA by July 31, 2020 in an amount of at least $30.0 million. The KKR Loans have a maturity date being the earliest of (a) January 3, 2025, or if Regulatory Approval has not occurred on or before December 31, 2020, January 15, 2021 and (b) the date that is 91 days prior to the earliest current maturity date of any other loans we might have in excess of $15.0 million prior to the funding of the third tranche of the KKR Loans or $25.0 million following the funding of the third tranche of the KKR Loans. The KKR Loans bear interest through maturity, at our election with respect to (a) Alternate Base Rate, or ABR Loans, ABR plus 6.50% per annum and (b) London Interbank Offered Rate, or LIBOR Loans, 30-day LIBOR plus 7.50% per annum. We have the option to elect to make interest payments from available funds or make interest payments in kind by capitalizing such interest amounts on the applicable interest payment date by adding the amounts to the outstanding principal amount of the loan. Any capitalized amounts also bear interest. To date, we have selected to pay in kind and capitalized the interest for the year ending December 31, 2019. We began accruing interest on the outstanding KKR Loans on March 31, 2019, and continue to accrue interest on the outstanding KKR loans on the last business day of each March, June, September and December thereafter while any KKR Loan is outstanding, as well as on the final maturity date of the KKR Loans, with each such date being referred to herein as an Interest Payment Date. Principal payments on the KKR Loans are paid according to the following schedule: (i) on December 31, 2023, 50.0% of the outstanding principal amount of the loans as of such date, including any capitalized interest, (ii) on each Interest Payment Date thereafter, 12.5% of the outstanding principal amount of the KKR Loans as of December 31, 2023 and (iii) on January 3, 2025, or the Maturity Date, any remaining outstanding balance of the KKR Loans. We are also required to make mandatory prepayments of the KKR Loans under the Agreement, subject to specified exceptions, with the proceeds of asset sales, debt issuances, royalty transactions, collaboration transactions, and specified other events. In addition, upon the occurrence of a change of control, we must prepay, the outstanding amount of the KKR Loans. The KKR Loans can be prepaid at our discretion, at any time, subject to prepayment fees. If all or any of the KKR Loans are prepaid or required to be prepaid, then we must pay, in addition to such prepayment, a prepayment premium (the “Prepayment Premium”) equal to (i) with respect to any such prepayment paid on or prior to January 3, 2021, the amount, if any, by which (a) the present value as of such date of determination of (x) 105.00% of the principal amount of the KKR Loans prepaid plus (y) all required interest payments that would have been due on the principal amount of the KKR Loans prepaid through and including January 3, 2021, computed using a discount rate equal to the treasury rate most nearly equal to the period from such date of prepayment to January 3, 2021 plus 50 basis points exceeds (b) the principal amount of the KKR Loans prepaid, (ii) with respect to any prepayment paid or required to be paid after January 3, 2021 but on or prior to January 3, 2022, 5.00% of the principal amount of the KKR Loans prepaid, (iii) with respect to any prepayment paid or required to be paid after January 3, 2022 but on or prior to January 3, 2023, 2.00% of the principal amount of the KKR Loans prepaid and (iv) with respect to any prepayment paid or required to be prepaid thereafter, 0.00% of the principal amount of the KKR Loans prepaid. In addition, upon the occurrence of a change of control, we must prepay, the outstanding amount of the KKR Loans. Upon the prepayment or repayment of all or any of the KKR Loans, we must pay an additional (in addition to the Prepayment Premium) exit fee in an amount equal to 4.00% of the principal amount of the KKR Loans prepaid or repaid. In addition, we paid certain customary fees and expenses to the Agent and other service providers upon the closing of the transaction. The obligations under the Credit Agreement are secured by a lien on substantially all of our tangible and intangible property. The Credit Agreement contains certain affirmative covenants, negative covenants and events of default, including, covenants and restrictions that among other things, require us and our subsidiary guarantors to satisfy a minimum cash balance covenant and restricts our ability and each of our subsidiaries’ ability to incur liens, incur additional indebtedness, make loans and investments, engage in mergers and acquisitions, engage in asset sales or sale and leaseback transactions, and declare dividends or redeem or repurchase capital stock. A failure to comply with these covenants could permit the Lenders under the Credit Agreement to declare the Term Loans, together with accrued interest and fees, to be immediately due and payable. In connection with the KKR Loans, we paid direct fees of $3.9 million, including debt issuance costs. The fees are being amortized as interest expense over the term of the debt. As of December 31, 2019, $44.0 million was outstanding under the KKR Loans. As of December 31, 2019, the interest rate on the KKR Loans was 9.20%. The following table represents our short-term and long-term debt obligations (in thousands): December 31, 2019 Principal amount of long-term debt $ 44,004 Less: Current portion of long-term debt — Long-term debt, net of current portion 44,004 Unamortized discount relating to deferred financing costs (3,234 ) Accrued exit fee payment 258 Long-term debt, net of discounts and current portion $ 41,028 Future principal payments of our long-term debt as of December 31, 2019 are as follows (in thousands): Fiscal year ending December 31: 2020 $ — 2021 — 2022 — 2023 22,002 2024 22,002 Thereafter — Total $ 44,004

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Leases Facility Leases We lease facilities for office and manufacturing space under various operating leases and a security system under a financing lease. Our leases have remaining lease terms of approximately 1 year to 6 years, which represent the non-cancellable periods of the leases and include extension options that we determined are reasonably certain to be exercised. We exclude extension options that are not reasonably certain to be exercised from our lease terms. Our lease payments consist primarily of fixed rental payments for the right to use the underlying leased assets over the lease terms. We often receive customary incentives from our landlords, such as reimbursements for tenant improvements and rent abatement periods, which effectively reduce the total lease payments owed for these leases. Operating lease right-of-use assets and liabilities on our consolidated balance sheets represent the present value of our remaining lease payments over the remaining lease terms. We do not allocate lease payments to non-lease components. We use our incremental borrowing rate to calculate the present value of our lease payments, as the implicit rates in our leases are not readily determinable. In 2015, we entered into lease agreements for our corporate headquarters in Brisbane, California for 38,000 square feet of office space, which was subsequently amended resulting in a total of approximately 58,000 square feet of office space being leased. The term for the entire office space terminates on June 30, 2024. We are responsible for operating expenses over base operating expenses as defined in the original lease agreement. In June 2015, we signed a facility lease for a manufacturing facility in Clearwater, Florida for approximately 20,000 square feet of manufacturing space, which was subsequently amended resulting in a total of approximately 30,000 square feet of manufacturing space being leased. The lease is expected to expire in June 2025 In September 2018, we entered into a lease for office space in Durham, North Carolina for 5,099 square feet of office space. The lease is expected to expire in February 2024 In November 2018, we entered into a lease for part of a floor of office space in London, United Kingdom. The lease is expected to expire in November 2023 Financing Lease In July 2016, we entered into a five-year Leases The maturities of our operating and financing lease liabilities are as follows (in thousands): Remaining Lease Payments at December 31, 2019 Operating Financing Total 2020 $ 3,772 $ 34 $ 3,806 2021 3,907 35 3,942 2022 3,961 9 3,970 2023 3,782 — 3,782 2024 1,857 — 1,857 Thereafter 227 — 227 Total lease payments 17,506 78 17,584 Less: Effects of discounting (4,725 ) (17 ) (4,742 ) Present value of lease liabilities 12,781 61 12,842 Less: current portion (2,257 ) (23 ) (2,280 ) Long-term lease liabilities $ 10,524 $ 38 $ 10,562 Weighted-average remaining lease term 4.5 years 2.3 years Weighted-average incremental borrowing rate 11 % 23 % The component of our lease costs included in our condensed consolidated statements of income were as follows (in thousands ): Year Ended December 31, 2019 2018 2017 Operating lease cost $ 3,753 $ 3,738 $ 2,320 Finance lease cost Amortization of leased assets 33 33 25 Interest on lease liabilities 16 19 16 Net lease cost $ 3,802 $ 3,790 $ 2,361 Other information related to our operating lease was as follows (in thousands): Other Information Year Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 3,753 Operating cash flows from finance leases $ 49 The future aggregate minimum lease payments calculated under ASC 840 at December 31, 2018 were as follows (in thousands): Remaining Lease Payments at December 31, 2018 Operating Financing Total 2019 $ 3,133 $ 33 $ 3,166 2020 3,330 34 3,364 2021 3,413 35 3,448 2022 3,497 9 3,506 2023 3,378 — 3,378 Thereafter 1,744 — 1,744 Total lease payments 18,495 111 18,606 Less: amount representing interest — (33 ) (33 ) Value of lease liabilities under ASC 840 18,495 78 18,573 Less: current portion (3,133 ) (17 ) (3,150 ) Long-term lease liabilities $ 15,362 $ 61 $ 15,423 Asset Retirement Obligation We recognized the estimated fair value of our asset retirement obligation related to our office space in London, United Kingdom in long-term liabilities in November 2018. The fair value of the asset retirement obligation is also capitalized as construction in progress. The fair value of the asset retirement obligation was estimated by discounting projected cash flows over the estimated life of the related assets using our credit adjusted risk-free rate. Our asset retirement obligation consists of a contractual requirement to remove the tenant improvements at our office space in London, United Kingdom and restore the lease office space to a condition as specified in the lease agreement. The following is the activity for our asset retirement obligation included in long-term liabilities (in thousands): Balance as of December 31, 2018 $ 88 Liabilities incurred during the year 11 Balance as of December 31, 2019 $ 99 Purchase Commitments We purchase food-grade peanut flour from Golden Peanut Company, or GPC, a wholly-owned subsidiary of Archer Daniels Midland, ten years five years In connection with the expansion and extension of the agreement, we issued Archer Daniels Midland Company 300,000 Pursuant with the restated agreement, our purchase obligation commences with the first delivery of peanut flour for commercial use, which we currently anticipate will occur in 2020. The aggregate purchase commitment under this agreement would be $5.6 million over a term of nine years. In December 2018, we entered into an exclusive supply agreement for egg protein with Michael Foods, Inc. Pursuant to the agreement, we have exclusive access to the clinical and commercial use of Michael Foods’ egg products for any egg allergy treatment, prevention or cure for a period of up to 15 years beyond the potential approval of AR201. In May 2019, we entered into a Commercial Supply Agreement, or the Commercial Supply Agreement, pursuant to which CoreRx, Inc. agreed to manufacture commercial supply of PALFORZIA, if approved. We are also required to purchase a minimum percentage or our P two-year In November 2019, we entered into a commercial packaging agreement, or the Commercial Packaging Agreement, with AndersonCrecon Inc. doing business as PCI of Illinois, or PCI, pursuant to which Commercial Packaging Agreement. In-Licensing Agreement In February 2020, we entered into a license agreement, or the License Agreement, with Xencor, Inc., or Xencor, for the exclusive, worldwide, royalty-bearing license for the development, manufacture and commercialization of biopharmaceutical products containing or comprising the humanized monoclonal antibody Initially, AIMab7195 will be developed as an adjunctive treatment with our existing CODIT pipeline assets, including PALFORZIA, to explore treatment outcomes, including the potential path to remission, in patients with food allergies. AIMab7195 is designed to mediate the suppression of IgE and IgE-producing cells and originally was developed for the treatment of allergic asthma and other IgE-mediated diseases. In connection with the entry into the License Agreement, we will pay Xencor an upfront payment of $5.0 million, and we issued to Xencor 156,238 shares of Common Stock, pursuant to a Securities Issuance Agreement with Xencor, dated February 4, 2020. Additionally, we are obligated to pay Xencor an aggregate of up to $380.0 million in milestone payments, which includes $17.0 million in development milestones, $53.0 million in regulatory milestones and $310.0 million in sales milestones, and to issue an additional number of shares of our Common Stock having an aggregate value of $5.0 million in connection with the achievement of the first development milestone with respect to a product containing an AIMab7195 Product. We will also pay a royalty to Xencor equal to a percentage of net sales of AIMab7195 Products in the high single-digit to mid-teen range. The term of the License Agreement continues on a country-by-country and Product-by-Product basis until the expiration of our obligation to pay royalties with respect such Product and country. We may terminate the License Agreement in its entirety without cause on sixty days’ prior written notice. Xencor may terminate the License Agreement in its entirety if the we or our affiliates or sublicensees challenge the licensed patents. Either party may terminate the License Agreement for the other party’s material breach that is not cured within a specified time period or for the other party’s bankruptcy or insolvency-related events. We will be solely responsible for costs related to the development of AIMab7195. In connection with our entry into the License Agreement, we also agreed to assume Xencor’s rights and obligations under its license of the AIMab7195 cell line from Catalent Pharma Solutions LLC, which manufactures AIMab7195 using their proprietary GPEx® technology. Indemnifications We indemnify each of our officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at our request in such capacity, as permitted under Delaware law and in accordance with its certificate of incorporation and bylaws. The term of the indemnification period lasts as long as an officer or a director may be subject to any proceeding arising out of acts or omissions of such officer or director in such capacity. The maximum amount of potential future indemnification is unlimited; however, we currently hold director and officer liability insurance. This insurance allows the transfer of risk associated with our exposure and may enable us to recover a portion of any future amounts paid. We believe that the fair value of these indemnification obligations is minimal. Accordingly, we have not recognized any liabilities relating to these obligations for any period. Legal We are currently not a party to any material legal proceedings. During the normal course of business, we may be a party to legal claims that may not be covered by insurance. We do not believe that any such claims would have a material impact on our consolidated financial statements.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Stockholders' Equity	7. Stockholders’ Equity Convertible Preferred Stock As of December 31, 2019 and 2018, we had authorized 10,000,000 shares of convertible preferred stock, and no shares of convertible preferred stock were issued and outstanding. In February 2020, Common Stock On November 23, 2016, we issued and sold 7,522,084 shares of our common stock, par value $0.0001 per share, for an aggregate cash purchase price of $145.0 million, pursuant to the Purchase Agreement, dated November 2, 2016, by and between us and Nestle Health Science. In connection with the closing of the Equity Investment, we and Nestle Health Science entered into a Registration Rights Agreement and a Standstill Agreement. Under the terms of the Registration Rights Agreement, upon the written request of Nestle Health Science, we shall prepare and file with the Securities and Exchange Commission, or the Commission, a registration statement covering the resale of all the shares sold to Nestle Health Science that are not then registered on an existing and effective registration statement for an offering to be made on a continuous basis pursuant Commission Rule 415. Additionally, we shall use commercially reasonable efforts to cause such registration statement filed under the Registration Rights Agreement to be declared effective under the Securities Act of 1933, as amended, within certain defined time limits and to keep such registration statement continuously effective for a period of potentially three years from the original effect date of such registration statement. Under the terms of the Standstill Agreement, Nestle Health Science is prohibited from entering into transactions with the shares purchased in the Equity Investment, as well as to enter into any transactions with any of our assets, without prior written consent of a majority of the members of our board of directors until the later of the end of the term of the Collaboration Agreement and November 23, 2018. In January 2018, w e issued Archer Daniels Midland Company 300,000 shares of restricted common stock, vesting in four tranches over a 3.5-year period. Refer to Note 6 for further information. In February and March 2018, we issued and sold an aggregate of 6,325,000 shares of our common stock in an underwritten public offering at a price to the public of $32.00 per share, including the closing of the full exercise of the underwriters’ option to purchase an additional 825,000 shares of common stock, In November 2018, we entered into an extension of the strategic collaboration on similar terms and issued and sold an additional 3,237,529 shares of our common stock in a private placement at a price of $30.27 per share for aggregate proceeds of $98.0 million, increasing Nestlé Health Science’s ownership of Aimmune to approximately 19%. The transaction documents include the extension of the registration rights, standstill rights and market standoff provisions. We are not subject to any partnership, collaboration, or negotiation restrictions under the extension agreements. In addition, we retain all rights to our current and future pipeline assets. In February 2020, we announced a $200.0 million equity investment by Nestle Health Science S.A. and the extension of their existing strategic collaboration designed to enable the development and commercialization of innovative food allergy therapies, which will terminate in November 2021.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation Equity Incentive Plan In July 2015, we adopted the 2015 Stock Plan, or the 2015 Plan. Under the 2015 Plan, 4,681,544 shares of our common stock were initially reserved for the issuance of stock options and restricted stock to employees, directors, and consultants under terms and provisions established by the Board of Directors, or the Board, and approved by our stockholders. As of December 31, 2019 and 2018 there were 4,599,005 shares and 4,364,963 shares available for future grant, respectively. Under the terms of the 2015 Plan, options may be granted at an exercise price not less than fair market value. For employees holding more than 10% of the voting rights of all classes of stock, the exercise prices for incentive stock options may not be less than 110% of fair market value, as determined by the Board. The terms of options granted under the 2015 Plan may not exceed ten years. All options issued to date have had a ten-year 1/48 th 1/24 th 1/48 th In August 2015, we adopted the 2015 ESPP, which commenced on January 1, 2018. Under the 2015 ESPP our employees may purchase common stock through payroll deductions at a price equal to 85% of the lower of the fair market value of the stock at the beginning of the offering period or at the end of each applicable purchase period. The 2015 ESPP generally provides for offering periods of six months in duration with purchase periods ending on either May 15 or November 15. Contributions under the 2015 ESPP are limited to a maximum of 15% of an employee’s eligible compensation. ESPP purchases are settled with common stock from the ESPP’s previously authorized and available pool of shares. As of December 31, 2019, we had issued 101,989 shares under the ESPP at a weighted average price of $17.67 per share and 2,303,797 shares under the ESPP remain available for purchase. We issued 41,030 shares at a weighted average price of $25.28 per share during the year ended December 31, 2018. Our 2013 Stock Plan, or the 2013 Plan, which was originally adopted during January 2013, was terminated upon consummation of our IPO in August 2015. As a terminated plan, no further options can be granted from the 2013 Plan, and no further shares are reserved for issuance under the 2013 Plan. Option activity under the 2015 Plan and 2013 Plan is set forth below: Options Outstanding Number Options Weighted- Average Exercise Price Weighted Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Balance, December 31, 2018 7,133,113 $ 20.08 7.6 $ 27,413 Options granted 3,156,942 $ 23.00 Options exercised and shares vested (1,442,889 ) $ 12.89 Options cancelled (1,217,343 ) $ 27.15 Balance, December 31, 2019 7,629,823 $ 21.52 8.0 $ 91,745 Options vested and expected to vest as of December 31, 2019 6,972,545 $ 21.23 7.9 $ 85,878 Options exercisable as of December 31, 2019 3,460,494 $ 18.09 6.9 $ 53,479 The aggregate intrinsic values of options outstanding, exercisable, and vested and expected to vest were calculated as the difference between the exercise price of the options and the market price for shares of our common stock as of December 31, 2019. The 2013 Plan provided for early exercise, therefore, all of the outstanding stock options issued under that plan are exercisable. The total intrinsic value of options exercised during the year ended December 31, 2019 was $18.2 million . Restricted stock unit, or RSU, activity under the 2015 Plan is set forth below: Shares Weighted Grant Date Fair Value Unvested Balance, December 31, 2018 309,847 $ 33.37 Awarded 485,027 22.98 Released (91,354 ) 33.28 Forfeited (172,725 ) 27.97 Unvested Balance, December 31, 2019 530,795 $ 25.79 RSUs are measured based on the fair market value of the underlying stock on the date of grant and recognized as expense on a straight-line basis over the employee’s requisite service period (generally the vesting period). In connection with the expansion and extension of our long-term exclusive commercial supply agreement with GPC, we issued 300,000 shares of restricted common stock in January 2018. The restricted common stock vests in four tranches over a 3.5-year period and is measured based on the fair market value of our common stock on December 31, 2018. As of December 31, 2019, 150,000 shares had vested, and the remaining shares were restricted. As of December 31, 2019, total estimated unrecognized expense related to these restricted shares was $2.7 million based upon the fair market value of our common stock on December 31, 2018, which is expected to be recognized over the remaining vesting period of 1.5 years as general and administrative expense. Stock-based compensation expense recognized during the years ended December 31, 2019 and 2018 related to these shares was $1.8 million and $3.0 million, respectively. As of December 31, 2019, we had issued 58,000 RSUs with a grant date fair value of approximately $1.4 million, to certain key employees that include service and performance vesting conditions related to the achievement of certain regulatory approvals for PALFORZIA. As the vesting for 46,000 RSUs was contingent upon specific performance conditions that were not met, they were cancelled with no stock-based compensation expense recognized. Valuation Assumptions The weighted-average assumptions used to estimate the fair value of stock options using the Black-Scholes option valuation model and the resulting weighted average fair value of stock options granted were as follows: Year Ended December 31, 2019 2018 2017 Expected term (in years) 6.0 6.0 6.0 Expected volatility 62.4 % 67.8 % 73.1 % Risk free interest rate 2.3 % 2.5 % 2.0 % Dividend yield — — — Weighted average estimated fair value $ 13.47 $ 19.53 $ 13.70 The weighted-average assumptions used to estimate the fair value of ESPP using the Black-Scholes option valuation model were as follows: Year Ended December 31, 2019 2018 2017 Expected term (in years) 0.5 0.8 — Expected volatility 51.0 % 50.2 % — Risk free interest rate 1.1 % 2.0 % — Dividend yield — — — Weighted average estimated fair value $ 7.32 $ 11.06 — Stock-Based Compensation Expense Stock-based compensation expense, net of estimated forfeitures, reflected in the consolidated statements of operations and comprehensive loss is as follows (in thousands): Year Ended December 31, 2019 2018 2017 Research and development $ 11,245 $ 9,945 $ 5,077 General and administrative 21,684 22,787 11,642 Total stock-based compensation expense $ 32,929 $ 32,732 $ 16,719 The fair value of options granted is expensed over the vesting period of the options, which is either four years or two years, on a straight-line basis as the services are being provided. No tax benefits were realized from options during the periods. During the years ended December 31, 2019, 2018 and 2017, we recorded approximately $2.5 million, $3.3 million and $0.4 million, respectively, of stock-based compensation expense related to the acceleration of certain former executives’ stock options. As of December 31, 2019, total unrecognized stock-based compensation expense and expected period over which such compensation will be recognized were as follows ($ in thousands): As of December 31, 2019 Stock-options Unrecognized stock compensation expense $ 48,246 Weighted-average remaining vesting period (years) 2.7 RSU Unrecognized stock compensation expense $ 7,887 Weighted-average remaining vesting period (years) 2.4 ESPP Unrecognized stock compensation expense $ 472 Weighted-average remaining vesting period (years) 0.4

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The following table presents loss before provision for income taxes (in thousands) : Year Ended December 31, 2019 2018 2017 Income/(loss) before income taxes Domestic $ (218,920 ) $ (176,085 ) $ (100,107 ) Foreign (28,861 ) (34,606 ) (31,162 ) Total loss before provision for income taxes $ (247,781 ) $ (210,691 ) $ (131,269 ) The federal, state and foreign income tax provisions for the years ended December 31, 2019, 2018 and 2017 are summarized as follows (in thousands): Year Ended December 31, 2019 2018 2017 Current Federal $ — $ — $ — State — — — Foreign 716 61 56 Total Current 716 61 56 Deferred Federal — — — State — — — Foreign — — — Total Deferred — — — Total provision for income taxes $ 716 $ 61 $ 56 Income tax expense for the years ended December 31, 2019, 2018 and 2017 differed from the amount expected by applying the statutory federal tax rate to the loss before taxes as summarized below (in thousands): Year Ended December 31, 2019 2018 2017 Federal tax benefit at statutory rate 21.00 % 21.00 % 34.00 % State tax benefit, net of federal benefit 1.16 % 0.82 % 0.54 % Stock compensation (0.85 )% (0.30 )% 1.72 % Change in valuation allowance (19.29 )% (19.29 )% (9.31 )% Research and development credits 1.26 % 1.65 % 1.70 % Foreign income taxed at different rates (2.74 )% (3.48 )% (8.11 )% Impact related to 2017 Tax Act 0.00 % 0.00 % (20.46 )% Other (0.83 )% (0.43 )% (0.12 )% Income tax expense (0.29 )% (0.03 )% (0.04 )% The significant components of our deferred taxes are as follows (in thousands): Year Ended December 31, 2019 2018 Deferred tax assets (liabilities): Net operating loss carryforwards $ 113,179 $ 70,831 Intangible asset 31,500 — Start-up costs 625 683 Stock-based compensation 6,277 6,387 Tax credit carryforwards 17,264 11,693 Operating lease liability 2,734 — Accruals 2,403 1,765 Other 828 482 Subtotal deferred tax assets 174,810 91,841 Less: valuation allowance (170,839 ) (91,520 ) Total deferred tax assets 3,971 321 Basis differences in fixed assets (1,492 ) (321 ) Operating lease right-of-use asset (2,479 ) — Net deferred income taxes $ — $ — We recognize deferred income taxes for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. We periodically evaluate the positive and negative evidence bearing upon realizability of our deferred tax assets. Based upon the weight of available evidence, which includes our historical operating performance, reported cumulative net losses since inception and difficulty in accurately forecasting our future results, we maintained a full valuation allowance on the net deferred tax assets as of December 31, 2019 and 2018. As of December 31, 2019, we had net operating loss, or NOL, carryforwards for Federal, California and other state income tax purposes of $522.3 12.0 63.9 As of December 31, 2019, we had Federal and California research credit carryforwards of $17.1 million and $5.7 million, respectively. As of December 31, 2018, we had Federal and California research credit carryforward of $12.1 million and $3.1 million, respectively. The Federal research credits will begin to expire in 2031, while the California research credits have no expiration date. Under Section 382 of the Internal Revenue Code of 1986, as amended, or the Code, if a corporation undergoes an “ownership change,” generally defined as a greater than 50 percentage point change (by value) in its equity ownership over a rolling three-year period, the corporation’s ability to use its pre-change net operating loss, or NOL, carryforwards to offset its post-change taxable income may be limited. Limitations may also apply to the utilization of other pre-change tax attributes as a result of an ownership change. Following the equity investment by Nestle Health Science in November 2016, we performed a Section 382 analysis and determined that we experienced multiple ownership changes under Section 382 of the Code prior to July 31, 2017. Utilization of the NOL and tax credit carryforwards are subject to a substantial annual limitation due to the ownership change limitations set forth in Internal Revenue Code Section 382 and similar state provisions. Such annual limitations could impact the utilization of NOL and tax credit carryforwards in the future. We experienced no significant permanent losses of tax attributes due to these ownership changes. In addition, we may experience more ownership changes under Section 382 of the Code as a result of future changes in our stock ownership, some of which may be outside our control. As a result, our ability to utilize NOL carryforwards or other tax attributes, such as research tax credits, in any taxable year may be further limited if we have experienced an ownership change. Tax benefits from uncertain tax positions are recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on technical merits. The amount recognized is measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon effective settlement. The following table summarizes the activity related to our unrecognized benefits (in thousands ): Year Ended December 31, 2019 2018 Beginning balance - unrecognized tax benefit, gross $ 3,055 $ 1,657 Increases related to tax positions taken during a prior year — — Decreases related to a tax position taken during a prior year — — Increases related to tax positions taken during the current year 4,750 1,398 Decreases related to settlements with taxing authorities — — Decreases related to expiration of statute of limitations — — Ending balance - unrecognized tax benefits, gross $ 7,805 $ 3,055 At December 31, 2019, the unrecognized tax benefits for uncertain tax positions were offset against the deferred tax assets and would not affect the income tax rate if recognized due to our being in a valuation allowance position. Our policy is to include interest and penalties related to unrecognized tax benefits, if any, within the provision for taxes in the consolidated statements of operations. We did not accrue any interest or penalties for the years ended December 31, 2019 and 2018. We do not have any tax positions for which it is reasonably possible that the total amount of gross unrecognized tax benefits will significantly change within 12 months of December 31, 2019. We file federal, state and foreign income tax returns in jurisdictions with varying statutes of limitations. Due to our NOL carryforwards, our income tax returns remain subject to examination by federal and most state taxing authorities for all tax years.

Defined Contribution Plan

Defined Contribution Plan	12 Months Ended
	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Defined Contribution Plan	10. Defined Contribution Plan We sponsor a 401(k) Plan, or the 401(k) Plan, which stipulates that eligible employees may contribute to the 401(k) Plan subject to certain limitations. We may match employee contributions in amounts to be determined at our sole discretion. Commencing in 2018, we began a discretionary matching of employee contributions up to a maximum match of $2,000 in any calendar year. We incurred total expenses of $0.4 million and $0.2 million for the years ended December 31, 2019 and 2018, respectively.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Related Party Transactions	11. Related Party Transactions In June 2017, Mark McDade, a member of our Board of Directors, joined the Board of Directors of MyHealthTeams, a private company that creates social networks for people living with chronic conditions by partnering with pharmaceutical and healthcare companies. We entered into an agreement with MyHealthTeams in 2015 under which they provide services to us. During the years ended December 31, 2019, 2018 and 2017, there were payments of $0.1 million, $0.1 million and $0.2 million, respectively, to MyHealthTeams pursuant to such agreement. At December 31, 2019 and 2018, there was no and $0.1 million accrued liabilities due under the MyHealthTeams agreement.

Selected Quarterly Results of O

Selected Quarterly Results of Operations (Unaudited)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Results of Operations (Unaudited)	12. Selected Quarterly Results of Operations (Unaudited) The following table presents our unaudited quarterly financial data. Our quarterly results of operations for these periods are not necessarily indicative of our future results of operations. Quarter Ended March 31 June 30 September 30 December 31 2019 (In thousands, except per share data) Operating expenses: Research and development $ 31,316 $ 31,988 $ 30,558 $ 30,125 General and administrative 23,712 31,200 34,044 36,861 Total operating expenses 55,028 63,188 64,602 66,986 Loss from operations (55,028 ) (63,188 ) (64,602 ) (66,986 ) Interest income 1,901 1,710 1,315 925 Interest expense (1,144 ) (1,262 ) (1,260 ) (1,250 ) Other income (expense), net 34 (90 ) (12 ) 1,156 Loss before provision (benefit) for income taxes (54,237 ) (62,830 ) (64,559 ) (66,155 ) Provision (benefit) for income taxes 29 48 (104 ) 743 Net loss $ (54,266 ) $ (62,878 ) $ (64,455 ) $ (66,898 ) Net loss per common share, basic and diluted $ (0.87 ) $ (1.01 ) $ (1.03 ) $ (1.06 ) Quarter Ended March 31 June 30 September 30 December 31 2018 (In thousands, except per share data) Operating expenses: Research and development $ 33,446 $ 35,254 $ 31,691 $ 33,029 General and administrative 16,673 18,559 21,285 25,404 Total operating expenses 50,119 53,813 52,976 58,433 Loss from operations (50,119 ) (53,813 ) (52,976 ) (58,433 ) Interest income 708 1,400 1,394 1,482 Interest expense (29 ) (28 ) (28 ) (28 ) Other expense, net (43 ) (78 ) (63 ) (37 ) Loss before provision (benefit) for income taxes (49,483 ) (52,519 ) (51,673 ) (57,016 ) Provision (benefit) for income taxes 17 33 29 (18 ) Net loss $ (49,500 ) $ (52,552 ) $ (51,702 ) $ (56,998 ) Net loss per common share, basic and diluted $ (0.92 ) $ (0.91 ) $ (0.89 ) $ (0.95 )

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of Preparation	Basis of Preparation The accompanying consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States, or U.S. GAAP, and include the accounts of our wholly-owned subsidiaries. All significant intercompany transactions have been eliminated. We operate in one reportable segment.
Foreign Currency Translation	Foreign Currency Translation Our functional currency and the functional currency of all of our subsidiaries is the United States dollar. Accordingly, monetary assets and liabilities in the non-functional currency of these subsidiaries are remeasured using exchange rates in effect at the end of the period. Costs in local currency are remeasured using average exchange rates for the period, except for costs related to those balance sheet items that are remeasured using historical exchange rates. The resulting remeasurement gains and losses are included in the consolidated statements of operations and comprehensive loss as incurred and have not been material for all periods presented.
Use of Estimates	Use of Estimates The preparation of the accompanying consolidated financial statements in accordance with U.S. GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of costs and expenses during the reporting period. We base our estimates and assumptions on historical experience when available and on various factors that we believe to be reasonable under the circumstances. We evaluate our estimates and assumptions on an ongoing basis. Our actual results could differ from these estimates under different assumptions or conditions.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid investments with original maturities of three months or less from the date of purchase to be cash equivalents. Cash equivalents, which are carried at estimated fair value, consist primarily of money market funds and certain available-for-sale investments with maturities of three months or less.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions regarding resource allocation and assessing performance. We operate in one reportable segment.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject us to a concentration of credit risk consist of cash and cash equivalents and certain investments in money market funds, agency securities, corporate securities, U.S. government securities and commercial paper. Bank deposits are primarily held by a single financial institution and these deposits may exceed insured limits. We are exposed to credit risk in the event of default by the financial institution holding our cash and cash equivalents and issuers of investments that are recorded on our consolidated balance sheets. We mitigate our risk by investing in high-grade instruments and limiting the concentration in any one issuer, which limits our exposure.
Investments	Investments Our investments consist of available-for-sale securities. Investments with original maturities of greater than 90 days but less than one (1) year are classified as short-term on the consolidated balance sheets. Investments with original maturities greater than one (1) year are classified as long-term on the consolidated balance sheets. Our investments in available-for-sale securities are reported at estimated fair value. Available-for-sale securities consist primarily of agency securities, corporate securities, U.S. government securities and commercial paper. Unrealized gains and losses related to changes in the fair value of securities are recognized in accumulated other comprehensive income or loss, net of tax, on our consolidated balance sheets. Changes in the fair value of available-for-sale securities impact the consolidated statements of operations and comprehensive loss only when such securities are sold or an other-than-temporary impairment is recognized. Realized gains and losses on the sale of securities are determined by specific identification of each security’s cost basis. We regularly review our investment portfolio to determine if any security is other-than-temporarily impaired, which would require us to record an impairment charge in the period any such determination is made. We consider factors such as the duration, severity and the reason for the decline in value, the financial condition of the issuer and any changes thereto, the potential recovery period and our intent to sell. For debt securities, we also consider whether (i) it is more likely than not that we will be required to sell the debt securities before recovery of their amortized cost basis, and (ii) the amortized cost basis cannot be recovered as a result of credit losses. Our assessment on whether a security is other-than-temporarily impaired could change in the future due to new developments or changes in assumptions related to any particular security.
Property and Equipment	Property and Equipment Property and equipment are stated at cost, less accumulated depreciation. Depreciation is computed using the straight-line method over the estimated useful lives of the respective assets. Maintenance and repairs are charged to the consolidated statements of operations and comprehensive loss as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss, if any, is reflected in the consolidated statements of operations and comprehensive loss. The useful lives of property and equipment are as follows: Computer equipment 3 years Furniture and office equipment 4 years Manufacturing equipment 7 years Buildings 25 years Leasehold improvements Shorter of remaining lease terms or useful life
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets We evaluate our long-lived assets, including property and equipment, for impairment whenever events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. Recoverability of these assets is measured by comparison of the carrying amount of each asset to the future undiscounted cash flows expected to result from the use of the asset and its eventual disposition. If the asset is considered to be impaired, the amount of any impairment is measured as the difference between the carrying value and the fair value of the impaired assets. We have not recorded impairment of any long-lived assets in the periods presented.
Leases	Leases Leases are classified as either finance or operating leases based on the principle of whether or not the lease is effectively a finance purchase by us. Lease expense is recognized over the term of the lease based on an effective interest method for finance leases and on a straight-line basis for operating leases. We also record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification.
Research and Development	Research and Development We expense research and development costs as incurred. We record accrued liabilities for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of pre-clinical studies and clinical trials, contract manufacturing activities and pre-approval inventory. These costs are a significant component of our research and development expenses. We accrue for these costs based on factors such as estimates of the work completed and in accordance with agreements established with our third-party service providers under the service agreements. We make significant judgments and estimates in determining the accrued liabilities balance in each reporting period. As actual costs become known, we adjust our accrued liabilities. We have not experienced any material differences between accrued costs and actual costs incurred. However, the status and timing of actual services performed, number of patients enrolled and the rate of patient enrollments may vary from our estimates, resulting in adjustments to expense in future periods. Changes in these estimates that result in material changes to our accruals could materially affect our results of operations.
Stock-based Compensation	Stock-Based Compensation We recognize compensation costs related to stock options granted to employees and directors based on the estimated fair value of the awards on the date of grant, net of estimated forfeitures. We estimate the grant date fair value using the Black-Scholes option-pricing model. The grant date fair value of the stock-based awards is generally recognized on a straight-line basis over the requisite service period, which is generally the vesting period of the respective awards. The fair value of the shares granted pursuant to the 2015 Employee Stock Purchase Plan, or the 2015 ESPP, In determining the fair value of the stock-based awards used to calculate stock-based compensation expense, we use the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires judgment to determine. • Expected Term. The expected term of stock-based awards represents the weighted average period the stock-based awards are expected to be outstanding. We have opted to use the simplified method for estimating the expected term as provided by the Securities and Exchange Commission Staff Accounting Bulletin, or SAB, 110 as our stock-based awards are considered “plain vanilla”. The simplified method calculates the expected term as the average time-to-vesting and the contractual life of the options. We plan to continue to use the simplified method under SAB 110 until we have sufficient exercise history as a publicly traded company. • Expected Volatility. As we have limited trading history for our common stock, the expected stock price volatility assumption is determined based on the historical volatilities of a group of industry peers as well as the historical volatility of our own common stock since we began trading subsequent to our IPO in August 2015. Industry peers consist of several public companies in the biopharmaceutical industry with comparable characteristics including enterprise value, risk profiles and position within the industry. We intend to continue to consistently apply this process using the same or similar public companies until a sufficient amount of historical information regarding the volatility of our own common stock share price becomes available, or unless circumstances change such that the identified companies are no longer similar to us, in which case, more suitable companies whose share prices are publicly available would be utilized in the calculation. • Risk-Free Interest Rate. The risk-free interest rate is based on the implied yield available on U.S. Treasury zero-coupon issues in effect at the time of grant for periods corresponding with the expected term of the stock-based award. • Expected Dividend Yield. We have never paid dividends on our common stock and have no plans to pay dividends on our common stock. Therefore, we used an expected dividend yield of zero for all years presented. Restricted Stock Units, or RSUs, are measured based on the fair market value of the underlying stock on the date of grant and recognized as expense on a straight-line basis over the employee’s requisite service period (generally the vesting period). In addition to the Black-Scholes assumptions, we estimate our forfeiture rate based on an analysis of our actual forfeitures and will continue to evaluate the adequacy of the forfeiture rate based on actual forfeiture experience, analysis of employee turnover behavior and other factors. The impact from any forfeiture rate adjustment would be recognized in full in the period of adjustment, and if the actual number of future forfeitures differs from our estimates, we might be required to record adjustments to stock-based compensation in future periods. We will continue to use judgment in evaluating the expected volatility, expected terms and forfeiture rates utilized for our stock-based compensation expense calculations on a prospective basis.
Income Taxes	Income Taxes We use the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of reported assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. We must then assess the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to our lack of earnings history, the net deferred tax assets have been fully offset by a valuation allowance. Tax benefits from uncertain tax positions are recognized when it is more likely than not that the position will be sustained upon examination, including resolutions of any related appeals or litigation processes, based on technical merits. The amount recognized is measured as the largest amount of tax benefit that is greater than 50% likely of being realized upon effective settlement.
Comprehensive Income or Loss	Comprehensive Income or Loss Comprehensive income or loss is defined as the change in equity during a period from transactions and other events, excluding changes resulting from investments from owners and distributions to owners. Other comprehensive loss includes net loss and unrealized gains and losses on available-for-sale investments.
Net Loss per Share	Net Loss per Share The following common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because their inclusion would have been antidilutive : Year Ended December 31, 2019 2018 2017 Stock options 7,629,823 7,133,113 6,629,111 Restricted stock units 530,795 309,847 16,638
Fair Value Measurements	Fair Value Measurements We define fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Our valuation techniques are based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect our market assumptions. We classify these inputs into the following hierarchy: Level 1 —Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date; Level 2 —Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities 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 related assets or liabilities; and Level 3 —Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. Financial instruments include cash equivalents, investments, accounts payable, and accrued liabilities. Our cash equivalents and investments are carried at estimated fair value and remeasured on a recurring basis. The carrying value of accounts payable and accrued liabilities approximate their estimated fair value due to the relatively short-term nature of these instruments. Our valuation techniques used to measure the fair value of money market funds were derived from quoted prices in active markets for identical assets. The valuation techniques used to measure the fair value of investments, all of which have counterparties with high credit ratings, were valued based on quoted market prices or model-driven valuations using significant inputs derived from or corroborated by observable market data. In accordance with fair value accounting requirements, companies may choose to measure eligible financial instruments and certain other items at fair value. We have not elected the fair value option for any eligible financial instruments.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements We adopted Accounting Standards Update, or ASU No. 2016-02, Leases (Topic 842) Lease (Topic 841): Targeted Improvements We adopted ASU No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting (Topic 718) We adopted ASU No. 2019-12, Simplifying the Accounting for Income Taxes
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In August 2018, the Financial Accounting Standards Board, or FASB, issued ASU 2018-13, Fair Value Measurement: Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement unobservable inputs used to develop Level 3 fair value measurements, and related changes in unrealized gains and losses included in other comprehensive income. ASU 2018-13 is effective for fiscal periods beginning after December 15, 2019, with early adoption permitted. We a dopt ed this guidance on January 1, 2020 . T he adoption of ASU 2018-13 will not have a material impact on the disclosures in our consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Schedule of Useful Lives of Property and Equipment	The useful lives of property and equipment are as follows: Computer equipment 3 years Furniture and office equipment 4 years Manufacturing equipment 7 years Buildings 25 years Leasehold improvements Shorter of remaining lease terms or useful life
Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss per Share	The following common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented because their inclusion would have been antidilutive : Year Ended December 31, 2019 2018 2017 Stock options 7,629,823 7,133,113 6,629,111 Restricted stock units 530,795 309,847 16,638

Available-for-Sale Securities_2

Available-for-Sale Securities and Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Summary of Financial Instruments Measured at Fair Value on a Recurring Basis	The following tables set forth our financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands ): December 31, 2019 Level 1 Level 2 Level 3 Total Cash and cash equivalents: Cash and money market funds $ 79,880 $ — $ — $ 79,880 Total cash and cash equivalents $ 79,880 $ — $ — $ 79,880 Investments: Agency securities — 8,862 — 8,862 Corporate securities — 30,338 — 30,338 Commercial paper — 7,949 — 7,949 U.S. government securities — 31,145 — 31,145 Total investments $ — $ 78,294 $ — $ 78,294 December 31, 2018 Level 1 Level 2 Level 3 Total Cash and cash equivalents: Cash and money market funds $ 107,511 $ — $ — $ 107,511 Total cash and cash equivalents $ 107,511 $ — $ — $ 107,511 Investments: Agency securities — 17,352 — 17,352 Corporate securities — 54,474 — 54,474 Commercial paper — 5,965 — 5,965 U.S. government securities — 118,630 — 118,630 Total investments $ — $ 196,421 $ — $ 196,421
Summary of Aggregate Market Value, Cost Basis and Gross Unrealized Gains and Losses of Available-for-Sale Investments by Security Type	The aggregate market value, cost basis, and gross unrealized gains and losses of available-for-sale investments by security type, classified in cash equivalents and investments, as of December 31, 2019 and 2018 are as follows (in thousands): December 31, 2019 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Total Fair Value Agency securities $ 8,856 $ 6 $ — $ 8,862 Corporate securities 30,286 55 (3 ) 30,338 Commercial paper 7,949 — — 7,949 U.S. government securities 31,123 22 — 31,145 Total available-for-sale investments $ 78,214 $ 83 $ (3 ) $ 78,294 December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Total Fair Value Agency securities $ 17,361 $ — $ (9 ) $ 17,352 Corporate securities 54,536 — (62 ) 54,474 Commercial paper 5,965 — — 5,965 U.S. government securities 118,667 14 (51 ) 118,630 Total available-for-sale investments $ 196,529 $ 14 $ (122 ) $ 196,421

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Summary of Property And Equipment, Net	Property and equipment, net consists of the following (in thousands): Year Ended December 31, 2019 2018 Furniture and equipment $ 2,660 $ 2,221 Computer equipment 2,820 2,073 Manufacturing equipment 9,012 1,733 Leased equipment 100 100 Leasehold improvements 14,525 4,469 Buildings — 688 Construction in progress 6,649 18,295 Property and equipment, gross 35,766 29,579 Less: accumulated depreciation (7,162 ) (3,251 ) Property and equipment, net $ 28,604 $ 26,328
Summary of Accrued Liabilities	Accrued liabilities consist of the following (in thousands ): Year Ended December 31, 2019 2018 Compensation and benefits $ 13,286 $ 8,912 Research and development 11,336 15,504 Professional and consulting 6,627 4,691 Other 37 37 Total accrued liabilities $ 31,286 $ 29,144

Long-Term Debt, Net of Discou_2

Long-Term Debt, Net of Discounts (Tables)	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Schedule of Short-term and Long-term Debt Obligations	The following table represents our short-term and long-term debt obligations (in thousands): December 31, 2019 Principal amount of long-term debt $ 44,004 Less: Current portion of long-term debt — Long-term debt, net of current portion 44,004 Unamortized discount relating to deferred financing costs (3,234 ) Accrued exit fee payment 258 Long-term debt, net of discounts and current portion $ 41,028
Schedule of Future Principal Payments of Long-term Debt	Future principal payments of our long-term debt as of December 31, 2019 are as follows (in thousands): Fiscal year ending December 31: 2020 $ — 2021 — 2022 — 2023 22,002 2024 22,002 Thereafter — Total $ 44,004

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Schedule of Maturities of Operating and Financing Lease Liabilities	The maturities of our operating and financing lease liabilities are as follows (in thousands): Remaining Lease Payments at December 31, 2019 Operating Financing Total 2020 $ 3,772 $ 34 $ 3,806 2021 3,907 35 3,942 2022 3,961 9 3,970 2023 3,782 — 3,782 2024 1,857 — 1,857 Thereafter 227 — 227 Total lease payments 17,506 78 17,584 Less: Effects of discounting (4,725 ) (17 ) (4,742 ) Present value of lease liabilities 12,781 61 12,842 Less: current portion (2,257 ) (23 ) (2,280 ) Long-term lease liabilities $ 10,524 $ 38 $ 10,562 Weighted-average remaining lease term 4.5 years 2.3 years Weighted-average incremental borrowing rate 11 % 23 %
Component of Lease Costs Included in Condensed Consolidated Statements of Income	The component of our lease costs included in our condensed consolidated statements of income were as follows (in thousands ): Year Ended December 31, 2019 2018 2017 Operating lease cost $ 3,753 $ 3,738 $ 2,320 Finance lease cost Amortization of leased assets 33 33 25 Interest on lease liabilities 16 19 16 Net lease cost $ 3,802 $ 3,790 $ 2,361
Schedule of Other Information Related to Operating Lease	Other information related to our operating lease was as follows (in thousands): Other Information Year Ended December 31, 2019 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows from operating leases $ 3,753 Operating cash flows from finance leases $ 49
Schedule of Future Aggregate Minimum Lease Payments Calculated under ASC 840	The future aggregate minimum lease payments calculated under ASC 840 at December 31, 2018 were as follows (in thousands): Remaining Lease Payments at December 31, 2018 Operating Financing Total 2019 $ 3,133 $ 33 $ 3,166 2020 3,330 34 3,364 2021 3,413 35 3,448 2022 3,497 9 3,506 2023 3,378 — 3,378 Thereafter 1,744 — 1,744 Total lease payments 18,495 111 18,606 Less: amount representing interest — (33 ) (33 ) Value of lease liabilities under ASC 840 18,495 78 18,573 Less: current portion (3,133 ) (17 ) (3,150 ) Long-term lease liabilities $ 15,362 $ 61 $ 15,423
Schedule of Activity for Asset Retirement Obligation Included in Long-Term Liabilities	The following is the activity for our asset retirement obligation included in long-term liabilities (in thousands): Balance as of December 31, 2018 $ 88 Liabilities incurred during the year 11 Balance as of December 31, 2019 $ 99

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Summary of Stock Option Activity	Option activity under the 2015 Plan and 2013 Plan is set forth below: Options Outstanding Number Options Weighted- Average Exercise Price Weighted Average Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Balance, December 31, 2018 7,133,113 $ 20.08 7.6 $ 27,413 Options granted 3,156,942 $ 23.00 Options exercised and shares vested (1,442,889 ) $ 12.89 Options cancelled (1,217,343 ) $ 27.15 Balance, December 31, 2019 7,629,823 $ 21.52 8.0 $ 91,745 Options vested and expected to vest as of December 31, 2019 6,972,545 $ 21.23 7.9 $ 85,878 Options exercisable as of December 31, 2019 3,460,494 $ 18.09 6.9 $ 53,479
Restricted Stock Unit Activity	Restricted stock unit, or RSU, activity under the 2015 Plan is set forth below: Shares Weighted Grant Date Fair Value Unvested Balance, December 31, 2018 309,847 $ 33.37 Awarded 485,027 22.98 Released (91,354 ) 33.28 Forfeited (172,725 ) 27.97 Unvested Balance, December 31, 2019 530,795 $ 25.79
Schedule of Weighted Average Assumptions to Fair Value of Stock Options	Valuation Assumptions The weighted-average assumptions used to estimate the fair value of stock options using the Black-Scholes option valuation model and the resulting weighted average fair value of stock options granted were as follows: Year Ended December 31, 2019 2018 2017 Expected term (in years) 6.0 6.0 6.0 Expected volatility 62.4 % 67.8 % 73.1 % Risk free interest rate 2.3 % 2.5 % 2.0 % Dividend yield — — — Weighted average estimated fair value $ 13.47 $ 19.53 $ 13.70
Summary of Stock-based Compensation Expense Net of Estimated Forfeitures	Stock-Based Compensation Expense Stock-based compensation expense, net of estimated forfeitures, reflected in the consolidated statements of operations and comprehensive loss is as follows (in thousands): Year Ended December 31, 2019 2018 2017 Research and development $ 11,245 $ 9,945 $ 5,077 General and administrative 21,684 22,787 11,642 Total stock-based compensation expense $ 32,929 $ 32,732 $ 16,719
Summary of Unrecognized Stock-Based Compensation Expense and Expected Period	As of December 31, 2019, total unrecognized stock-based compensation expense and expected period over which such compensation will be recognized were as follows ($ in thousands): As of December 31, 2019 Stock-options Unrecognized stock compensation expense $ 48,246 Weighted-average remaining vesting period (years) 2.7 RSU Unrecognized stock compensation expense $ 7,887 Weighted-average remaining vesting period (years) 2.4 ESPP Unrecognized stock compensation expense $ 472 Weighted-average remaining vesting period (years) 0.4
Employee Stock Purchase Plan
Schedule of Weighted Average Assumptions to Fair Value of Stock Options	The weighted-average assumptions used to estimate the fair value of ESPP using the Black-Scholes option valuation model were as follows: Year Ended December 31, 2019 2018 2017 Expected term (in years) 0.5 0.8 — Expected volatility 51.0 % 50.2 % — Risk free interest rate 1.1 % 2.0 % — Dividend yield — — — Weighted average estimated fair value $ 7.32 $ 11.06 —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Schedule of Loss Before Provision for Income Taxes	The following table presents loss before provision for income taxes (in thousands) : Year Ended December 31, 2019 2018 2017 Income/(loss) before income taxes Domestic $ (218,920 ) $ (176,085 ) $ (100,107 ) Foreign (28,861 ) (34,606 ) (31,162 ) Total loss before provision for income taxes $ (247,781 ) $ (210,691 ) $ (131,269 )
Summary of Federal, State and Foreign Income Tax Provisions	The federal, state and foreign income tax provisions for the years ended December 31, 2019, 2018 and 2017 are summarized as follows (in thousands): Year Ended December 31, 2019 2018 2017 Current Federal $ — $ — $ — State — — — Foreign 716 61 56 Total Current 716 61 56 Deferred Federal — — — State — — — Foreign — — — Total Deferred — — — Total provision for income taxes $ 716 $ 61 $ 56
Summary of Income Tax Expense Differed from Statutory Federal Tax Rate to the Loss Before Taxes	Income tax expense for the years ended December 31, 2019, 2018 and 2017 differed from the amount expected by applying the statutory federal tax rate to the loss before taxes as summarized below (in thousands): Year Ended December 31, 2019 2018 2017 Federal tax benefit at statutory rate 21.00 % 21.00 % 34.00 % State tax benefit, net of federal benefit 1.16 % 0.82 % 0.54 % Stock compensation (0.85 )% (0.30 )% 1.72 % Change in valuation allowance (19.29 )% (19.29 )% (9.31 )% Research and development credits 1.26 % 1.65 % 1.70 % Foreign income taxed at different rates (2.74 )% (3.48 )% (8.11 )% Impact related to 2017 Tax Act 0.00 % 0.00 % (20.46 )% Other (0.83 )% (0.43 )% (0.12 )% Income tax expense (0.29 )% (0.03 )% (0.04 )%
Significant Components of the Company's Deferred Taxes	The significant components of our deferred taxes are as follows (in thousands):
Summary of Activity Related to Unrecognized Benefits	The following table summarizes the activity related to our unrecognized benefits (in thousands ): Year Ended December 31, 2019 2018 Beginning balance - unrecognized tax benefit, gross $ 3,055 $ 1,657 Increases related to tax positions taken during a prior year — — Decreases related to a tax position taken during a prior year — — Increases related to tax positions taken during the current year 4,750 1,398 Decreases related to settlements with taxing authorities — — Decreases related to expiration of statute of limitations — — Ending balance - unrecognized tax benefits, gross $ 7,805 $ 3,055

Selected Quarterly Results of_2

Selected Quarterly Results of Operations (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Schedule of Unaudited Quarterly Financial Data	The following table presents our unaudited quarterly financial data. Our quarterly results of operations for these periods are not necessarily indicative of our future results of operations. Quarter Ended March 31 June 30 September 30 December 31 2019 (In thousands, except per share data) Operating expenses: Research and development $ 31,316 $ 31,988 $ 30,558 $ 30,125 General and administrative 23,712 31,200 34,044 36,861 Total operating expenses 55,028 63,188 64,602 66,986 Loss from operations (55,028 ) (63,188 ) (64,602 ) (66,986 ) Interest income 1,901 1,710 1,315 925 Interest expense (1,144 ) (1,262 ) (1,260 ) (1,250 ) Other income (expense), net 34 (90 ) (12 ) 1,156 Loss before provision (benefit) for income taxes (54,237 ) (62,830 ) (64,559 ) (66,155 ) Provision (benefit) for income taxes 29 48 (104 ) 743 Net loss $ (54,266 ) $ (62,878 ) $ (64,455 ) $ (66,898 ) Net loss per common share, basic and diluted $ (0.87 ) $ (1.01 ) $ (1.03 ) $ (1.06 ) Quarter Ended March 31 June 30 September 30 December 31 2018 (In thousands, except per share data) Operating expenses: Research and development $ 33,446 $ 35,254 $ 31,691 $ 33,029 General and administrative 16,673 18,559 21,285 25,404 Total operating expenses 50,119 53,813 52,976 58,433 Loss from operations (50,119 ) (53,813 ) (52,976 ) (58,433 ) Interest income 708 1,400 1,394 1,482 Interest expense (29 ) (28 ) (28 ) (28 ) Other expense, net (43 ) (78 ) (63 ) (37 ) Loss before provision (benefit) for income taxes (49,483 ) (52,519 ) (51,673 ) (57,016 ) Provision (benefit) for income taxes 17 33 29 (18 ) Net loss $ (49,500 ) $ (52,552 ) $ (51,702 ) $ (56,998 ) Net loss per common share, basic and diluted $ (0.92 ) $ (0.91 ) $ (0.89 ) $ (0.95 )

Formation and Business of the_2

Formation and Business of the Company - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Feb. 29, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Organization And Description Of Business [Line Items]
Net loss		$ 66,898	$ 64,455	$ 62,878	$ 54,266	$ 56,998	$ 51,702	$ 52,552	$ 49,500	$ 248,497	$ 210,752	$ 131,325
Net cash used in operating activities										195,408	169,128	$ 99,605
Accumulated deficit		724,680				$ 476,234				724,680	$ 476,234
Cash, cash equivalents and investments		$ 158,200								$ 158,200
Scenario, Forecast | NHScUS
Organization And Description Of Business [Line Items]
Proceeds from issuance of common stock and convertible preferred stock	$ 200,000
Scenario, Forecast | KKR Loans | NHScUS
Organization And Description Of Business [Line Items]
Proceeds from issuance of common stock and convertible preferred stock	200,000
Draw of the second loan tranche	$ 85,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019USD ($)Segment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Significant Accounting Policies [Line Items]
Number of reportable segments | Segment	1
Impairment of any long lived assets	$ 0	$ 0	$ 0
Operating lease, right-of-use asset	11,512,000
Operating lease, liability	12,781,000
ASU 2016-02
Significant Accounting Policies [Line Items]
Operating lease, right-of-use asset	11,500,000
Operating lease, liability	$ 12,800,000
Minimum
Significant Accounting Policies [Line Items]
Tax benefit recognized upon effective settlement percentage	50.00%
Dividend Yield
Significant Accounting Policies [Line Items]
Alternative investment, measurement input	0

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2019
Computer Equipment
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	3 years
Furniture And Office Equipment
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	4 years
Manufacturing Equipment
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	7 years
Buildings
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	25 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Useful lives of property and equipment	Shorter of remaining lease terms or useful life

Summary of Significant Accoun_6

Summary of Significant Accounting Policies -Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	7,629,823	7,133,113	6,629,111
Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	530,795	309,847	16,638

Available-for-Sale Securities_3

Available-for-Sale Securities and Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Investments:
Total investments	$ 78,294	$ 196,421
Agency Securities
Investments:
Total investments	8,862	17,352
Corporate Debt Securities
Investments:
Total investments	30,338	54,474
Commercial Paper
Investments:
Total investments	7,949	5,965
U.S. Government Securities
Investments:
Total investments	31,145	118,630
Fair Value Measurements Recurring
Cash and cash equivalents
Total cash and cash equivalents	79,880	107,511
Investments:
Total investments	78,294	196,421
Fair Value Measurements Recurring | Cash and Money Market Funds
Cash and cash equivalents
Total cash and cash equivalents	79,880	107,511
Fair Value Measurements Recurring | Agency Securities
Investments:
Total investments	8,862	17,352
Fair Value Measurements Recurring | Corporate Debt Securities
Investments:
Total investments	30,338	54,474
Fair Value Measurements Recurring | Commercial Paper
Investments:
Total investments	7,949	5,965
Fair Value Measurements Recurring | U.S. Government Securities
Investments:
Total investments	31,145	118,630
Level 1 | Fair Value Measurements Recurring
Cash and cash equivalents
Total cash and cash equivalents	79,880	107,511
Level 1 | Fair Value Measurements Recurring | Cash and Money Market Funds
Cash and cash equivalents
Total cash and cash equivalents	79,880	107,511
Level 2 | Fair Value Measurements Recurring
Investments:
Total investments	78,294	196,421
Level 2 | Fair Value Measurements Recurring | Agency Securities
Investments:
Total investments	8,862	17,352
Level 2 | Fair Value Measurements Recurring | Corporate Debt Securities
Investments:
Total investments	30,338	54,474
Level 2 | Fair Value Measurements Recurring | Commercial Paper
Investments:
Total investments	7,949	5,965
Level 2 | Fair Value Measurements Recurring | U.S. Government Securities
Investments:
Total investments	$ 31,145	$ 118,630

Available-for-Sale Securities_4

Available-for-Sale Securities and Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair value assets transfers between level 1 to level 2	$ 0	$ 0
Fair value assets transfers between level 2 to level 1	$ 0	0
Available-for-sale securities, maturities period	2 years
Other than temporary impairment losses	$ 0	$ 0	$ 0
Marketable securities unrealized losses position maximum period	12 months

Available-for-Sale Securities_5

Available-for-Sale Securities and Fair Value Measurements - Summary of Aggregate Market Value, Cost Basis, and Gross Unrealized Gains and Losses of Available for Sale Investments by Security Type (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	$ 78,214	$ 196,529
Gross Unrealized Gains	83	14
Gross Unrealized Losses	(3)	(122)
Total investments	78,294	196,421
Agency Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	8,856	17,361
Gross Unrealized Gains	6
Gross Unrealized Losses		(9)
Total investments	8,862	17,352
Corporate Debt Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	30,286	54,536
Gross Unrealized Gains	55
Gross Unrealized Losses	(3)	(62)
Total investments	30,338	54,474
Commercial Paper
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	7,949	5,965
Total investments	7,949	5,965
U.S. Government Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	31,123	118,667
Gross Unrealized Gains	22	14
Gross Unrealized Losses		(51)
Total investments	$ 31,145	$ 118,630

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 35,766	$ 29,579
Less: accumulated depreciation	(7,162)	(3,251)
Property and equipment, net	28,604	26,328
Furniture and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,660	2,221
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,820	2,073
Manufacturing Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	9,012	1,733
Leased Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	100	100
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	14,525	4,469
Buildings
Property Plant And Equipment [Line Items]
Property and equipment, gross		688
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 6,649	$ 18,295

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Depreciation Expense	$ 4,086	$ 1,598	$ 966

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued Liabilities Current [Abstract]
Compensation and benefits	$ 13,286	$ 8,912
Research and development	11,336	15,504
Professional and consulting	6,627	4,691
Other	37	37
Total accrued liabilities	$ 31,286	$ 29,144

Long-Term Debt, Net of Discou_3

Long-Term Debt, Net of Discounts - Additional Information (Details)	Dec. 31, 2023	Jan. 03, 2021	Jul. 31, 2020USD ($)	Jan. 31, 2019USD ($)Tranche	Dec. 31, 2019USD ($)	Jan. 01, 2021USD ($)	Dec. 31, 2020USD ($)	Feb. 29, 2020USD ($)
Debt Instrument [Line Items]
Payment of fees including debt issuance costs					$ 3,856,000
Long term debt, outstanding					$ 44,004,000
KKR Loans
Debt Instrument [Line Items]
Loan agreement, maximum borrowing capacity				$ 170,000,000
Debt instrument number of tranches | Tranche				3
Loan agreement, proceeds receivable upon closing of transaction				$ 40,000,000
Loan agreement, remaining borrowing capacity upon certain conditions				$ 45,000,000
Line of credit facility maturity date				Jan. 3, 2025
Regulatory approval last date				Dec. 31, 2020
Line of credit facility without regulatory approval expiration date				Jan. 15, 2021
Loan prepayment fee percentage, after January 3, 2021 but on or prior to January 3, 2022					5.00%
Loan prepayment fee percentage, after January 3, 2022 but on or prior to January 3, 2023					2.00%
Loan prepayment fee percentage, thereafter					0.00%
Loan exit fee percentage					4.00%
Payment of fees including debt issuance costs					$ 3,900,000
Long term debt, outstanding					$ 44,000,000
Debt instrument, interest rate					9.20%
KKR Loans | Scenario, Forecast
Debt Instrument [Line Items]
Loan agreement, proceeds receivable upon FDA approval								$ 85,000,000
Other loans trigger amount to reduce 91 days maturity of credit facility						$ 25,000,000	$ 15,000,000
Loan, spread on variable rate		0.50%
Loan redemption price, percentage	50.00%
Line of credit facility, interest rate	12.50%
Percentage of principal amount of loans prepayment paid on or prior to January 3, 2021		105.00%
KKR Loans | Alternate Base Rate
Debt Instrument [Line Items]
Loan, spread on variable rate				6.50%
KKR Loans | 30-day LIBOR
Debt Instrument [Line Items]
Loan, spread on variable rate				7.50%
KKR Loans | Minimum | Scenario, Forecast
Debt Instrument [Line Items]
Achievement of aggregate net sales			$ 30,000,000

Long-Term Debt, Net of Discou_4

Long-Term Debt, Net of Discounts - Schedule of Short-term and Long-term Debt Obligations (Details) $ in Thousands	Dec. 31, 2019USD ($)
Debt Disclosure [Abstract]
Principal amount of long-term debt	$ 44,004
Long-term debt, net of current portion	44,004
Unamortized discount relating to deferred financing costs	(3,234)
Accrued exit fee payment	258
Long-term debt, net of discounts and current portion	$ 41,028

Long-Term Debt, Net of Discou_5

Long-Term Debt, Net of Discounts - Schedule of Future Principal Payments of Long-Term Debt (Details) $ in Thousands	Dec. 31, 2019USD ($)
Debt Disclosure [Abstract]
2023	$ 22,002
2024	22,002
Total	$ 44,004

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	Feb. 04, 2020USD ($)shares	May 31, 2019	Nov. 30, 2018	Sep. 30, 2018ft²	Jan. 31, 2018USD ($)Trancheshares	Jun. 30, 2015ft²	Dec. 31, 2019USD ($)ft²	Dec. 31, 2018shares	Dec. 31, 2015ft²
Commitments And Contingencies [Line Items]
Operating lease, description							We lease facilities for office and manufacturing space under various operating leases and a security system under a financing lease.
Finance Lease, Description							We lease facilities for office and manufacturing space under various operating leases and a security system under a financing lease.
Operating lease, existence of option to extend							true
Operating lease, option to extend							Our leases have remaining lease terms of approximately 1 year to 6 years, which represent the non-cancellable periods of the leases and include extension options that we determined are reasonably certain to be exercised. We exclude extension options that are not reasonably certain to be exercised from our lease terms.
Finance lease, existence of option to extend							true
Finance lease, option to extend							Our leases have remaining lease terms of approximately 1 year to 6 years, which represent the non-cancellable periods of the leases and include extension options that we determined are reasonably certain to be exercised. We exclude extension options that are not reasonably certain to be exercised from our lease terms.
Operating lease, variable lease payment, terms and conditions							We use our incremental borrowing rate to calculate the present value of our lease payments, as the implicit rates in our leases are not readily determinable.
Finance lease, variable lease payment, terms and conditions							We use our incremental borrowing rate to calculate the present value of our lease payments, as the implicit rates in our leases are not readily determinable.
Lease, termination date							Jun. 30, 2024
Term of capital lease agreement							5 years
Common Stock
Commitments And Contingencies [Line Items]
Number of common stock issued | shares								6,325,000
Archer Daniels Midland Company
Commitments And Contingencies [Line Items]
Long-term purchase commitment, restated agreement effective period after first delivery					10 years
Long-term purchase commitment, optional extension period					5 years
Long-term purchase commitment amount							$ 5,600,000
Long-term purchase commitment period							9 years
Archer Daniels Midland Company | Restricted Stock | Common Stock
Commitments And Contingencies [Line Items]
Long-term purchase commitment, shares issued | shares					300,000
Long-term purchase commitment, shares issued, vesting period					3 years 6 months
Long-term purchase commitment, fair value					$ 11,700,000
Number of tranches for vesting of shares | Tranche					4
CoreRx, Inc.
Commitments And Contingencies [Line Items]
Long-term purchase commitment amount							$ 43,800,000
Long-term purchase commitment period							5 years
Long-term purchase commitment expiration date		Dec. 31, 2024
Long-term purchase commitment renewal term		2 years
CoreRx, Inc. | PALFORZIA Commercial Supply Requirements
Commitments And Contingencies [Line Items]
Percentage of long term purchase commitment minimum required quantity		100.00%
Number of years for minimum supply percentage after approval		6 years
Annual purchase commitments beginning year		2019
Annual purchase commitments ending year		2024
CoreRx, Inc. | PALFORZIA Commercial Supply Requirements for Release Testing
Commitments And Contingencies [Line Items]
Percentage of long term purchase commitment minimum required quantity		100.00%
Number of years for minimum supply percentage after approval		6 years
Annual purchase commitments beginning year		2019
Annual purchase commitments ending year		2024
AndersonCrecon Inc.
Commitments And Contingencies [Line Items]
Long-term purchase commitment amount							$ 3,000,000
Long-term purchase commitment period							4 years
Xencor, Inc. | In-Licensing Agreement | Subsequent Event
Commitments And Contingencies [Line Items]
Upfront payable	$ 5,000,000
Aggregate amount payable under development milestone payments	17,000,000
Aggregate amount payable under regulatory milestone payments	53,000,000
Aggregate amount payable under sales milestone payments	310,000,000
Aggregate value of common stock	$ 5,000,000
Xencor, Inc. | Common Stock | In-Licensing Agreement | Subsequent Event
Commitments And Contingencies [Line Items]
Number of common stock issued | shares	156,238
Facility Leases
Commitments And Contingencies [Line Items]
Leased area | ft²				5,099
Lease, termination date			Nov. 30, 2023	Feb. 29, 2024		Jun. 30, 2025
Facility Leases | Corporate Headquarters
Commitments And Contingencies [Line Items]
Leased area | ft²							58,000		38,000
Facility Leases | Manufacturing Facility
Commitments And Contingencies [Line Items]
Leased area | ft²						20,000	30,000
Minimum
Commitments And Contingencies [Line Items]
Remaining lease terms							1 year
Maximum
Commitments And Contingencies [Line Items]
Remaining lease terms							6 years
Maximum | Michael Foods, Inc.
Commitments And Contingencies [Line Items]
Long-term purchase commitment period							15 years
Maximum | Xencor, Inc. | In-Licensing Agreement | Subsequent Event
Commitments And Contingencies [Line Items]
Aggregate amount payable under milestone payments	$ 380,000,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Maturities of Operating and Financing Lease Liabilities (Details) $ in Thousands	Dec. 31, 2019USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating lease, 2020	$ 3,772
Operating lease, 2021	3,907
Operating lease, 2022	3,961
Operating lease, 2023	3,782
Operating lease, 2024	1,857
Operating lease, Thereafter	227
Operating Lease, Total lease payments	17,506
Less: Operating lease, Effects of discounting	(4,725)
Operating lease, Present value of lease liabilities	12,781
Less: Operating lease, current portion	(2,257)
Operating lease, Long-term lease liabilities	$ 10,524
Operating Lease, Weighted-average remaining lease term	4 years 6 months
Operating Lease, Weighted-average incremental borrowing rate	11.00%
Financing lease, 2020	$ 34
Financing lease, 2021	35
Financing lease, 2022	9
Financing lease, Total lease payments	78
Less: Financing lease, Effects of discounting	(17)
Financing lease, Present value of lease liabilities	61
Less: Financing lease, current portion	(23)
Financing lease, Long-term lease liabilities	$ 38
Financing lease, Weighted-average remaining lease term	2 years 3 months 18 days
Financing lease, Weighted-average incremental borrowing rate	23.00%
Remaining Lease Payments, 2020	$ 3,806
Remaining Lease Payments, 2021	3,942
Remaining Lease Payments, 2022	3,970
Remaining Lease Payments, 2023	3,782
Remaining Lease Payments, 2024	1,857
Remaining Lease Payments, Thereafter	227
Total lease payments	17,584
Less: Effects of discounting	(4,742)
Present value of lease liabilities	12,842
Less: current portion	(2,280)
Long-term lease liabilities	$ 10,562

Commitments and Contingencies_3

Commitments and Contingencies - Component of Lease Costs Included in Condensed Consolidated Statements of Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Lease Cost [Abstract]
Operating lease cost	$ 3,753	$ 3,738	$ 2,320
Finance lease cost
Amortization of leased assets	33	33	25
Interest on lease liabilities	16	19	16
Net lease cost	$ 3,802	$ 3,790	$ 2,361

Commitments and Contingencies_4

Commitments and Contingencies - Schedule of Other Information Related to Operating Lease (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$ 3,753
Operating cash flows from finance leases	$ 49

Commitments and Contingencies_5

Commitments and Contingencies - Schedule of Future Aggregate Minimum Lease Payments Calculated under ASC 840 (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating Lease, 2019	$ 3,133
Operating Lease, 2020	3,330
Operating Lease, 2021	3,413
Operating Lease, 2022	3,497
Operating Lease, 2023	3,378
Operating Lease, Thereafter	1,744
Operating Lease, Total lease payments	18,495
Less: Operating Lease, current portion	(3,133)
Operating Lease, Long-term lease liabilities	15,362
Financing Lease, 2019	33
Financing Lease, 2020	34
Financing Lease, 2021	35
Financing Lease, 2022	9
Total financing lease payments	111
Less: Financing Lease, amount representing interest	(33)
Financing Lease Value of lease liabilities under ASC 840	78
Less: Financing Lease, current portion	(17)
Financing Lease, Long-term lease liabilities	61
Remaining Lease Payments, 2019	3,166
Remaining Lease Payments, 2020	3,364
Remaining Lease Payments, 2021	3,448
Remaining Lease Payments, 2022	3,506
Remaining Lease Payments, 2023	3,378
Remaining Lease Payments, Thereafter	1,744
Total lease payments	18,606
Less: amount representing interest	(33)
Value of lease liabilities under ASC 840	18,573
Less: current portion	(3,150)
Long-term lease liabilities	$ 15,423

Commitments and Contingencies_6

Commitments and Contingencies - Schedule of Activity for Asset Retirement Obligation Included in Long-Term Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Commitments And Contingencies Disclosure [Abstract]
Beginning Balance	$ 88
Liabilities incurred during the year	11
Ending Balance	$ 99

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) $ / shares in Units, $ in Thousands	Nov. 23, 2016USD ($)$ / sharesshares	Feb. 29, 2020USD ($)$ / sharesshares	Nov. 30, 2018USD ($)$ / sharesshares	Jan. 31, 2018Trancheshares	Mar. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)	Dec. 31, 2019$ / sharesshares
Stockholders Equity [Line Items]
Preferred stock, shares authorized						10,000,000		10,000,000
Preferred stock, shares issued						0		0
Preferred stock, shares outstanding						0		0
Issuance of common stock upon securities purchase agreement					6,325,000
Common stock, par value | $ / shares						$ 0.0001		$ 0.0001
Proceeds from issuance of common stock | $						$ 288,435	$ 6,520
Underwritten public offering price per share | $ / shares					$ 32
Proceeds from issuance of common stock | $					$ 190,400
Underwriter
Stockholders Equity [Line Items]
Purchase of additional shares of common stock					825,000
Common Stock
Stockholders Equity [Line Items]
Issuance of shares						6,325,000
Archer Daniels Midland Company | Common Stock | Restricted Stock
Stockholders Equity [Line Items]
Long-term purchase commitment, shares issued				300,000
Number of tranches for vesting of shares | Tranche				4
Long-term purchase commitment, shares issued, vesting period				3 years 6 months
NHScUS
Stockholders Equity [Line Items]
Ownership percentage			19.00%
NHScUS | Purchase Agreement
Stockholders Equity [Line Items]
Issuance of common stock upon securities purchase agreement	7,522,084
Common stock, par value | $ / shares	$ 0.0001
Proceeds from issuance of common stock | $	$ 145,000
NHScUS | Private Placement
Stockholders Equity [Line Items]
Issuance of shares			3,237,529
Share issued price | $ / shares			$ 30.27
Proceeds from issuance of common stock | $			$ 98,000
NHScUS | Scenario, Forecast
Stockholders Equity [Line Items]
Proceeds from issuance of common stock and convertible preferred stock | $		$ 200,000
Equity investment | $		$ 200,000
NHScUS | Common Stock | Scenario, Forecast
Stockholders Equity [Line Items]
Issuance of shares		1,000,000
Share issued price | $ / shares		$ 31.97
Convertible Preferred Stock
Stockholders Equity [Line Items]
Preferred stock, shares authorized						10,000,000		10,000,000
Preferred stock, shares issued						0		0
Preferred stock, shares outstanding						0		0
Convertible Preferred Stock | NHScUS | Scenario, Forecast
Stockholders Equity [Line Items]
Issuance of shares		525,634
Share issued price | $ / shares		$ 319.675

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended			12 Months Ended
	Jan. 31, 2018	Aug. 31, 2015	Jul. 31, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Intrinsic Value of option exercised				$ 18,200,000
Number of shares available for grant				3,156,942
Former Executive
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Accelerated stock compensation expense				$ 2,500,000	$ 3,300,000	$ 400,000
Restricted Stock | Common Stock | Archer Daniels Midland Company
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period	3 years 6 months
Long-term purchase commitment, shares issued	300,000
Long-term purchase commitment, shares issued, vesting period					3 years 6 months
Stock-based compensation, shares vested				150,000
Unrecognized employee stock-based compensation					$ 2,700,000
Expected recognized over weighted-average remaining vesting period				1 year 6 months
Stock-based compensation expense				$ 1,800,000	$ 3,000,000
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Recognized stock-based compensation expense				$ 7,887,000
Restricted Stock Units (RSUs) | Certain Key Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of restricted stock issued				58,000
Restricted stock units, aggregate grant date fair value				$ 1,400,000
Shares vesting on contingent upon specific performance conditions, cancelled				46,000
Recognized stock-based compensation expense				$ 0
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Tax benefit realized from option				$ 0
Maximum | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period				4 years
Minimum | Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period				2 years
2015 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares reserved for issuance			4,681,544
Number of shares available for future grant				4,599,005	4,364,963
Minimum percentage of voting rights of all classes of stock			10.00%
Percentage of statutory stock options			110.00%
Options expiration period			10 years
2015 Plan | Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares vesting on contingent upon specific performance conditions, cancelled				172,725
2015 Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options expiration period			10 years
2015 Plan | First Anniversary
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period			4 years
Option vesting rights, percentage			25.00%
2015 Plan | Thereafter
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option vesting rights, percentage			2.08%
2015 Plan | Over Two Years
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period			2 years
Option vesting rights, percentage			4.17%
2015 Plan | Over Four Years
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period			4 years
Option vesting rights, percentage			2.08%
2015 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of statutory stock options		85.00%
Description of ESPP				Under the 2015 ESPP our employees may purchase common stock through payroll deductions at a price equal to 85% of the lower of the fair market value of the stock at the beginning of the offering period or at the end of each applicable purchase period. The 2015 ESPP generally provides for offering periods of six months in duration with purchase periods ending on either May 15 or November 15. Contributions under the 2015 ESPP are limited to a maximum of 15% of an employee’s eligible compensation.
Percentage of maximum contributions employee's eligible compensation		15.00%
ESPP offering period		6 months
Description of offering period closing dates				The 2015 ESPP generally provides for offering periods of six months in duration with purchase periods ending on either May 15 or November 15.
Shares issued under the plan				101,989	41,030
Weighted average price per share				$ 17.67	$ 25.28
Employee stock purchase plan remain available for purchase				2,303,797
2013 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares reserved for issuance				0
Number of shares available for future grant				0

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Number of Options
Number of Options, Beginning Balance	7,133,113
Number of Options, Options granted	3,156,942
Number of Options, Options exercised and shares vested	(1,442,889)
Number of Options, Options cancelled	(1,217,343)
Number of Options, Ending Balance	7,629,823	7,133,113
Number of Options, Options vested and expected to vest as of December 31, 2019	6,972,545
Number of Options, Options exercisable as of December 31, 2019	3,460,494
Weighted-Average Exercise Price
Weighted-Average Exercise Price, Beginning Balance	$ 20.08
Weighted-Average Exercise Price, Options granted	23
Weighted-Average Exercise Price, Options exercised and shares vested	12.89
Weighted-Average Exercise Price, Options cancelled	27.15
Weighted-Average Exercise Price, Ending Balance	21.52	$ 20.08
Weighted-Average Exercise Price, Options vested and expected to vest as of December 31, 2019	21.23
Weighted-Average Exercise Price, Options exercisable as of December 31, 2019	$ 18.09
Weighted Average Remaining Contractual Life (in years)
Weighted Average Remaining Contractual Life (in years), Balance	8 years	7 years 7 months 6 days
Weighted Average Remaining Contractual Life, Options vested and expected to vest as of December 31, 2019	7 years 10 months 24 days
Weighted Average Remaining Contractual Life, Options exercisable as of December 31, 2019	6 years 10 months 24 days
Aggregate Intrinsic Value, Balance	$ 91,745	$ 27,413
Aggregate Intrinsic Value, Options vested and expected to vest as of December 31, 2019	85,878
Aggregate Intrinsic Value, Options exercisable as of December 31, 2019	$ 53,479

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Unit Activity (Details) - 2015 Plan - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested Shares, Beginning Balance | shares	309,847
Shares, Awarded | shares	485,027
Shares, Released | shares	(91,354)
Shares, Forfeited | shares	(172,725)
Unvested Shares, Ending Balance | shares	530,795
Unvested Weighted Average Grant Date Fair Value, Beginning Balance | $ / shares	$ 33.37
Weighted Average Grant Date Fair Value, Awarded | $ / shares	22.98
Weighted Average Grant Date Fair Value, Released | $ / shares	33.28
Weighted Average Grant Date Fair Value, Forfeited | $ / shares	27.97
Weighted Average Grant Date Fair Value, Ending Balance | $ / shares	$ 25.79

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Weighted Average Assumptions to Fair Value of Stock Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years	6 years	6 years
Expected volatility	62.40%	67.80%	73.10%
Risk free interest rate	2.30%	2.50%	2.00%
Weighted average estimated fair value	$ 13.47	$ 19.53	$ 13.70
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 months	9 months 18 days	0 years
Expected volatility	51.00%	50.20%
Risk free interest rate	1.10%	2.00%
Weighted average estimated fair value	$ 7.32	$ 11.06

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock-based Compensation Expense Net of Estimated Forfeitures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 32,929	$ 32,732	$ 16,719
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	11,245	9,945	5,077
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 21,684	$ 22,787	$ 11,642

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Unrecognized Stock-Based Compensation Expense and Expected Period (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock compensation expense	$ 48,246
Weighted-average remaining vesting period (years)	2 years 8 months 12 days
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average remaining vesting period (years)	2 years 4 months 24 days
Unrecognized stock compensation expense	$ 7,887
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted-average remaining vesting period (years)	4 months 24 days
Unrecognized stock compensation expense	$ 472

Income Taxes - Schedule of Loss

Income Taxes - Schedule of Loss Before Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income/(loss) before income taxes
Domestic									$ (218,920)	$ (176,085)	$ (100,107)
Foreign									(28,861)	(34,606)	(31,162)
Loss before provision for income taxes	$ (66,155)	$ (64,559)	$ (62,830)	$ (54,237)	$ (57,016)	$ (51,673)	$ (52,519)	$ (49,483)	$ (247,781)	$ (210,691)	$ (131,269)

Income Taxes - Summary of Feder

Income Taxes - Summary of Federal, State and Foreign Income Tax Provisions (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current
Foreign									$ 716	$ 61	$ 56
Total Current									716	61	56
Deferred
Total provision for income taxes	$ 743	$ (104)	$ 48	$ 29	$ (18)	$ 29	$ 33	$ 17	$ 716	$ 61	$ 56

Income Taxes - Summary of Incom

Income Taxes - Summary of Income Tax Expense Differed from Statutory Federal Tax Rate to the Loss Before Taxes (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal tax benefit at statutory rate	21.00%	21.00%	34.00%
State tax benefit, net of federal benefit	1.16%	0.82%	0.54%
Stock compensation	(0.85%)	(0.30%)	1.72%
Change in valuation allowance	(19.29%)	(19.29%)	(9.31%)
Research and development credits	1.26%	1.65%	1.70%
Foreign income taxed at different rates	(2.74%)	(3.48%)	(8.11%)
Impact related to 2017 Tax Act	0.00%	0.00%	(20.46%)
Other	(0.83%)	(0.43%)	(0.12%)
Income tax expense	(0.29%)	(0.03%)	(0.04%)

Income Taxes - Significant Comp

Income Taxes - Significant Components of the Company's Deferred Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets (liabilities):
Net operating loss carryforwards	$ 113,179	$ 70,831
Intangible asset	31,500
Start-up costs	625	683
Stock-based compensation	6,277	6,387
Tax credit carryforwards	17,264	11,693
Operating lease liability	2,734
Accruals	2,403	1,765
Other	828	482
Subtotal deferred tax assets	174,810	91,841
Less: valuation allowance	(170,839)	(91,520)
Total deferred tax assets	3,971	321
Basis differences in fixed assets	(1,492)	$ (321)
Operating lease right-of-use asset	$ (2,479)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Net change in valuation allowance	$ 79,300,000	$ 41,600,000
Interest and penalties related to unrecognized tax benefits	0	0
Federal
Operating Loss Carryforwards [Line Items]
Operating loss, Net	$ 522,300,000	326,400,000
Net operating loss carryforward expiration year	2031
Research credit carryforwards	$ 17,100,000	12,100,000
Research credit carryforward expiration year	2031
Other State
Operating Loss Carryforwards [Line Items]
Operating loss, Net	$ 63,900,000	30,200,000
Net operating loss carryforward expiration year	2030
California
Operating Loss Carryforwards [Line Items]
Operating loss, Net	$ 12,000,000	12,000,000
Net operating loss carryforward expiration year	2031
Research credit carryforwards	$ 5,700,000	$ 3,100,000

Income Taxes - Summary of Activ

Income Taxes - Summary of Activity Related to Unrecognized Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Beginning balance - unrecognized tax benefit, gross	$ 3,055	$ 1,657
Increases related to tax positions taken during the current year	4,750	1,398
Ending balance - unrecognized tax benefits, gross	$ 7,805	$ 3,055

Defined Contribution Plan - Add

Defined Contribution Plan - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Plan Disclosure [Line Items]
Total expenses incurred towards discretionary matching contribution by employer	$ 400,000	$ 200,000
Maximum
Defined Contribution Plan Disclosure [Line Items]
Discretionary matching contribution by employer	$ 2,000

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - MyHealth Teams - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Payments to service agreement	$ 100,000	$ 100,000	$ 200,000
Accrued liabilities due	$ 0	$ 100,000

Selected Quarterly Results of_3

Selected Quarterly Results of Operations (Unaudited) - Schedule of Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating expenses
Research and development	$ 30,125	$ 30,558	$ 31,988	$ 31,316	$ 33,029	$ 31,691	$ 35,254	$ 33,446	$ 123,987	$ 133,420	$ 89,325
General and administrative	36,861	34,044	31,200	23,712	25,404	21,285	18,559	16,673	125,817	81,921	43,949
Total operating expenses	66,986	64,602	63,188	55,028	58,433	52,976	53,813	50,119	249,804	215,341	133,274
Loss from operations	(66,986)	(64,602)	(63,188)	(55,028)	(58,433)	(52,976)	(53,813)	(50,119)	(249,804)	(215,341)	(133,274)
Interest income	925	1,315	1,710	1,901	1,482	1,394	1,400	708	5,851	4,984	2,190
Interest expense	(1,250)	(1,260)	(1,262)	(1,144)	(28)	(28)	(28)	(29)	(4,916)	(113)	(114)
Other income (expense), net	1,156	(12)	(90)	34	(37)	(63)	(78)	(43)	1,088	(221)	(71)
Loss before provision for income taxes	(66,155)	(64,559)	(62,830)	(54,237)	(57,016)	(51,673)	(52,519)	(49,483)	(247,781)	(210,691)	(131,269)
Provision (benefit) for income taxes	743	(104)	48	29	(18)	29	33	17	716	61	56
Net loss	$ (66,898)	$ (64,455)	$ (62,878)	$ (54,266)	$ (56,998)	$ (51,702)	$ (52,552)	$ (49,500)	$ (248,497)	$ (210,752)	$ (131,325)
Net loss per common share, basic and diluted	$ (1.06)	$ (1.03)	$ (1.01)	$ (0.87)	$ (0.95)	$ (0.89)	$ (0.91)	$ (0.92)	$ (3.97)	$ (3.67)	$ (2.61)