Ngm Biopharmaceuticals (NGM) 10-K 15 Mar 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Mar. 10, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	NGM
Entity Registrant Name	NGM BIOPHARMACEUTICALS INC
Entity Central Index Key	0001426332
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		76,692,401
Entity File Number	001-38853
Entity Tax Identification Number	26-1679911
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Address, Address Line One	333 Oyster Point Boulevard
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	243-5555
Entity Interactive Data Current	Yes
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Title of 12(b) Security	Common Stock, par value $0.001 per share
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Entity Public Float			$ 457
ICFR Auditor Attestation Flag	false
Documents Incorporated by Reference	Portions of the registrant’s definitive Proxy Statement for the 2021 Annual Meeting of Stockholders to be filed with the U.S. Securities and Exchange Commission pursuant to Regulation 14A not later than 120 days after the end of the fiscal year covered by this Annual Report on Form 10-K are incorporated by reference in Part III, Items 10-14 of this Annual Report on Form 10-K.

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 147,017	$ 245,598
Short-term marketable securities	148,139	98,913
Related party receivable from collaboration	333	5,206
Related party contract asset	6,100
Prepaid expenses and other current assets	6,837	5,531
Total current assets	308,426	355,248
Property and equipment, net	14,526	19,475
Restricted cash	1,499	1,874
Other non-current assets	4,592	3,806
Total assets	329,043	380,403
Current liabilities:
Accounts payable	9,663	9,026
Accrued liabilities	29,945	22,991
Deferred rent, current	2,975	2,829
Contract liabilities		4,872
Total current liabilities	42,583	39,718
Non-current liabilities:
Deferred rent, non-current	6,417	9,392
Early exercise stock option liability		574
Total liabilities	49,000	49,684
Commitments and contingencies (Note 6)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued or outstanding as of December 31, 2020 and 2019, respectively
Common stock, $0.001 par value; 400,000,000 shares authorized; 70,585,364 and 66,960,279 shares issued and outstanding as of December 31, 2020 and 2019, respectively	71	67
Additional paid-in capital	578,599	526,771
Accumulated other comprehensive gain	4	25
Accumulated deficit	(298,631)	(196,144)
Total stockholders' equity	280,043	330,719
Total liabilities and stockholders' equity	$ 329,043	$ 380,403

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
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	$ 0.001	$ 0.001
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	70,585,364	66,960,279
Common stock, shares outstanding	70,585,364	66,960,279

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Related party revenue	$ 87,368	$ 103,544	$ 108,665
Operating expenses:
Research and development	163,972	129,253	95,714
General and administrative	27,229	23,631	17,265
Total operating expenses	191,201	152,884	112,979
Loss from operations	(103,833)	(49,340)	(4,314)
Interest income	1,939	6,692	3,622
Other income (expense), net	(593)	(147)	199
Net loss	$ (102,487)	$ (42,795)	$ (493)
Net loss per share, basic and diluted	$ (1.50)	$ (0.85)	$ (0.08)
Weighted average shares used to compute net loss per share, basic and diluted	68,475,378	50,297,524	6,383,751

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (102,487)	$ (42,795)	$ (493)
Other comprehensive gain (loss), net of tax:
Net unrealized gain (loss) on available-for-sale marketable securities	(21)	292	164
Total comprehensive loss	$ (102,508)	$ (42,503)	$ (329)

CONSOLIDATED STATEMENTS OF CONV

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Cumulative Effect Period of Adoption Adjustment	Convertible Preferred Stock	Common Stock	Additional Paid-In Capital	Other Comprehensive Gain (Loss)	Accumulated Deficit	Accumulated DeficitCumulative Effect Period of Adoption Adjustment
Balance at Dec. 31, 2017	$ (120,978)		$ 294,874	$ 6	$ 26,147	$ (431)	$ (146,700)
Balance, shares at Dec. 31, 2017			47,267,000	6,105,000
Issuance of common stock to participants in 401(k) Plan	91				91
Issuance of common stock to participants in 401(k) Plan, shares				11,000
Issuance of common stock upon exercise of stock options	2,583			$ 1	2,582
Issuance of common stock upon exercise of stock options, shares				479,000
Vesting of common stock from early exercises	764				764
Vesting of common stock from early exercises, shares				161,000
Repurchase of common stock	(185)				(185)
Repurchase of common stock, shares				(23,000)
Stock-based compensation expense	9,859				9,859
Changes in unrealized gain on available-for-sale securities, net of tax	164					164
Net loss	(493)						(493)
Balance at Dec. 31, 2018	$ (108,195)	$ (6,156)	$ 294,874	$ 7	39,258	(267)	(147,193)	$ (6,156)
Balance, shares at Dec. 31, 2018			47,267,000	6,733,000
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201409Member
Net exercise of preferred stock warrant to Series A preferred stock			$ 198
Net exercise of preferred stock warrant to Series A preferred stock, shares			16,000
Conversion of Series A, B, C, D, E convertible preferred stock to common stock	$ 295,072		$ (295,072)	$ 47	295,025
Conversion of Series A, B, C, D, E convertible preferred stock to common stock, shares			(47,283,000)
Conversion of Series A, B, C, D, E convertible preferred stock to common stock, shares				47,283,000
Issuance of common stock upon initial public offering, net of issuance costs	107,756			$ 8	107,748
Issuance of common stock upon initial public offering, net of issuance costs, shares				7,521,000
Issuance of common stock upon private placement	65,947			$ 4	65,943
Issuance of common stock upon private placement, shares				4,122,000
Issuance of common stock to participants in 401(k) Plan	98				98
Issuance of common stock to participants in 401(k) Plan, shares				8,000
Issuance of common stock upon exercise of stock options	3,575			$ 1	3,574
Issuance of common stock upon exercise of stock options, shares				984,000
Issuance of common stock in connection with employee stock purchase plan	1,270				1,270
Issuance of common stock in connection with employee stock purchase plan, shares				103,000
Vesting of common stock from early exercises	993				993
Vesting of common stock from early exercises, shares				132,000
Stock-based compensation expense	12,862				12,862
Changes in unrealized gain on available-for-sale securities, net of tax	292					292
Net loss	(42,795)						(42,795)
Balance at Dec. 31, 2019	330,719			$ 67	526,771	25	(196,144)
Balance, shares at Dec. 31, 2019				66,886,000
Issuance of common stock to participants in 401(k) Plan	119				119
Issuance of common stock to participants in 401(k) Plan, shares				6,000
Issuance of common stock upon exercise of stock options	$ 11,838			$ 3	11,835
Issuance of common stock upon exercise of stock options, shares	2,614,842			2,616,000
Issuance of common stock under Open Market Agreement, net of issuance cost	$ 21,330			$ 1	21,329
Issuance of common stock shares, under Open Market Agreement, net of issuance cost				810,000
Issuance of common stock in connection with employee stock purchase plan	2,370				2,370
Issuance of common stock in connection with employee stock purchase plan, shares				197,000
Vesting of common stock from early exercises	524				524
Vesting of common stock from early exercises, shares				68,000
Stock-based compensation expense	15,651				15,651
Changes in unrealized gain on available-for-sale securities, net of tax	(21)					(21)
Net loss	(102,487)						(102,487)
Balance at Dec. 31, 2020	$ 280,043			$ 71	$ 578,599	$ 4	$ (298,631)
Balance, shares at Dec. 31, 2020				70,583,000

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net loss	$ (102,487)	$ (42,795)	$ (493)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	6,555	7,605	7,223
Amortization of discount on marketable securities	(128)	(1,123)	(876)
Stock-based compensation expense	15,651	12,862	9,859
Other non-cash expenses	613	217	271
Changes in operating assets and liabilities:
Related party receivable from collaboration	4,873	(1,537)	(3,669)
Related party contract asset	(6,100)
Prepaid expenses and other assets	(1,864)	(1,988)	(4,365)
Accounts payable	910	3,642	3,484
Accrued and other liabilities	6,182	8,877	4,059
Deferred rent	(2,829)	(2,683)	(1,957)
Contract liabilities	(4,872)	(24,251)	(21,133)
Net cash used in operating activities	(83,496)	(41,174)	(7,597)
Cash flows from investing activities
Purchase of marketable securities	(177,655)	(134,306)	(133,609)
Proceeds from sales and maturities of marketable securities	128,536	186,518	178,182
Purchase of property and equipment	(1,879)	(3,489)	(5,844)
Net cash provided by (used in) investing activities	(50,998)	48,723	38,729
Cash flows from financing activities
Proceeds from initial public offering, net of issuance costs		109,959
Proceeds from private placement of common stock		65,947
Proceeds from Open Market Agreement	21,943
Proceeds from exercise of stock options	11,838	3,575	2,583
Proceeds from employee stock purchase plan	2,370	1,270
Repurchase of common stock			(185)
Deferred offering costs paid	(613)		(2,200)
Net cash provided by financing activities	35,538	180,751	198
Net increase (decrease) in cash and cash equivalents	(98,956)	188,300	31,330
Cash, cash equivalents and restricted cash at beginning of period	247,472	59,172	27,842
Cash, cash equivalents and restricted cash at end of period	148,516	247,472	59,172
Supplemental disclosures of cash flow information
Net exercise of convertible preferred stock warrant to Series A preferred stock		198
Vesting of common stock from early exercises	524	993	764
Property and equipment purchases accrued and not yet paid	20	$ 305	607
Deferred offering costs accrued and not yet paid	$ 228		$ 92

Organization and Description of

Organization and Description of Business	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Description of Business	1. Organization and Description of Business NGM Biopharmaceuticals, Inc. and its wholly-owned subsidiary, collectively referred to as the Company, is focused on discovering and developing novel therapeutics based on scientific understanding of key biological pathways underlying liver and metabolic diseases, retinal diseases and cancer. The Company’s robust portfolio of product candidates range from early discovery to late-stage development and include aldafermin, MK-3655, NGM621, NGM120, NGM707 and NGM438. The Company has additional undisclosed programs that are in various stages of development ranging from functional validation to preclinical development. The Company was incorporated in Delaware in December 2007 and commenced operations in 2008. The Company’s headquarters are located at 333 Oyster Point Blvd., South San Francisco, California 94080. Stock Split On March 22, 2019, the Company filed an amendment to the Company’s amended and restated certificate of incorporation to effect a reverse split of shares of the Company’s common stock on a two-for-one basis, or the Reverse Stock Split. In connection with the Reverse Stock Split, the conversion ratio for the Company’s outstanding convertible preferred stock was proportionately adjusted such that the common stock issuable upon conversion of such preferred stock was decreased in proportion to the Reverse Stock Split. The par value of the common stock was not adjusted as a result of the Reverse Stock Split. All references to common stock, options to purchase common stock, early exercised options, share data, per share data, convertible preferred stock (to the extent presented on an as-converted to common stock basis) and related information contained in these consolidated financial statements have been retrospectively adjusted to reflect the effect of the Reverse Stock Split for all periods presented. Initial Public Offering On April 8, 2019, the Company closed the initial public offering, or IPO, of its common stock. In connection with the IPO, the Company sold an aggregate of 7,521,394 shares of common stock, including 854,727 shares sold pursuant to the underwriters’ exercise of their option to purchase additional shares, at a public offering price of $16.00 per share. The aggregate net proceeds received by the Company for shares sold in the offering was $107.8 million, after deducting underwriting discounts, commissions and offering expenses of $4.1 million, of which $2.2 million were paid in 2018. Upon the closing of the IPO, all shares of the Company’s outstanding convertible preferred stock were automatically converted to 47,283,839 shares of common stock and the related carrying amount of $295.1 million was reclassified to common stock and additional paid-in capital within stockholders’ equity (deficit). Concurrent with the closing of the IPO, the Company also issued 4,121,683 shares of its common stock to Merck Sharp & Dohme Corp., or Merck, in a private placement at a price of $16.00 per share for proceeds of $65.9 million, which resulted in Merck owning approximately 19.9% of the Company’s outstanding shares of common stock at that time.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation The consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or U.S. GAAP, and include the consolidated accounts of the Company and its wholly-owned subsidiary in Australia. All intercompany balances and transactions have been eliminated upon consolidation. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make judgments, assumptions and estimates that affect the amounts reported in the consolidated financial statements and accompanying notes. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. Actual results could differ materially from those estimates. Uses and Sources of Liquidity Since inception, the Company has incurred net losses and negative cash flow from operations. During the years ended December 31, 2020, 2019 and 2018, the Company incurred net losses of $102.5 million, $42.8 million and $0.5 million, respectively. As of December 31, 2020, the Company had an accumulated deficit of $298.6 million. The Company expects its accumulated deficit will increase significantly over time and does not expect to experience positive cash flows from operations in the near future. In December 2020, under an Open Market Sale Agreement SM As of December 31, 2020, the Company had $295.2 million of cash, cash equivalents and short-term marketable securities. In January 2021, the Company sold 5,324,074 shares of its common stock through an underwritten public offering at a price of $27.00 per share for aggregate net proceeds of approximately $134.7 million after deducting underwriting discounts and commissions and other estimated offering expenses payable by the Company. See Note 10 for additional information. The Company believes that the net proceeds from this offering, together with its existing cash, cash equivalents and short-term marketable securities, will be sufficient to fund its operations for a period of at least one year from the date these consolidated financial statements are issued. To fully implement the Company’s business plan and fund its operations, the Company will need to raise additional capital through public or private equity offerings (which may include potential net proceeds from future sales, if any, under the Sales Agreement), debt financings, government or other third-party funding, collaborations, strategic alliances and licensing arrangements or a combination of the foregoing. Fair Value of Financial Instruments The carrying amounts of cash and cash equivalents, the related party receivable from collaboration and other current assets and liabilities approximate their respective fair values due to their short-term nature. Cash and Cash Equivalents Cash and cash equivalents are stated at fair value. Cash equivalents are securities with an original maturity of three months or less at the time of purchase. The Company limits its credit risk associated with cash and cash equivalents by placing its investments with a bank it believes is highly creditworthy and with highly rated money market funds. As of December 31, 2020 and 2019, cash and cash equivalents consisted of bank deposits and investments in money market funds. Marketable Securities The appropriate classification of the Company’s marketable securities is determined at the time of purchase and such designations are re-evaluated at each balance sheet date. All of the Company’s securities are considered as available-for-sale and carried at estimated fair values and reported in cash equivalents and short-term marketable securities. Unrealized gains and losses on available-for-sale securities are excluded from net loss and reported in accumulated other comprehensive gain as a separate component of stockholders’ equity. Other income (expense), net, includes interest, amortization of purchase premiums and accretion of purchase discounts, realized gains and losses on sales of securities and other-than-temporary declines in the fair value of securities, if any. The cost of securities sold is based on the specific identification method. The Company’s investments are regularly reviewed for other-than-temporary declines in fair value. This review includes the consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. When the Company determines that the decline in fair value of an investment is below its carrying value and this decline is other-than-temporary, the Company reduces the carrying value of the security it holds and records a loss for the amount of such decline. As of December 31, 2020, the Company did not record any impairment related to other-than-temporary declines in the fair value of securities. Restricted Cash The Company’s restricted cash balance represents collateral required under the Company’s facility lease agreement and is classified as a non-current asset on the consolidated balance sheets, as the collateral will not be returned to the Company in 2021. Concentration of Credit and Other Risks Cash and cash equivalents and marketable securities from the Company’s available-for-sale and marketable security portfolio potentially subject the Company to concentrations of credit risk. The Company is invested in money market funds and marketable securities through custodial relationships with major U.S. and Australian banks. Under its investment policy, the Company limits amounts invested in such securities by credit rating, maturity, industry group, investment type and issuer, except for securities issued by the U.S. government. Related party receivables from collaborations are typically unsecured. Accordingly, the Company may be exposed to credit risk generally associated with its current collaboration agreement with Merck and any future collaboration agreements with other collaboration partners. To date, the Company has not experienced any losses related to these receivables. Amounts recognized as revenue prior to the Company having an unconditional right (other than a right that is conditioned only on the passage of time) to receipt are recorded as contract assets in the Company's consolidated balance sheets. Although the Company expects to have an unconditional right to receive such amounts, the Company may be exposed to the risk of not receiving the recorded amounts under its current collaboration agreement with Merck and any future collaboration agreements with other collaboration partners. To date, the Company has not experienced any losses related to contract assets. Merck accounted for 100% of the Company’s revenue for the years ended December 31, 2020, 2019 and 2018. Property and Equipment, Net Property and equipment is recorded at cost and consists of computer equipment, laboratory equipment and office furniture and leasehold improvements. Maintenance and repairs, and training on the use of equipment, are expensed as incurred. Costs that improve assets or extend their economic lives are capitalized. Depreciation is recognized using the straight-line method based on an estimated useful life of the asset, which is as follows: Computer equipment 3 years Laboratory equipment and office furniture 3 years Leasehold improvement Shorter of life of asset or lease term Leases The Company’s lease agreements for its laboratory and office facilities are classified as operating leases. Rent expense is recognized on a straight-line basis over the term of the lease. Incentives granted under the Company’s facilities leases, including allowances to fund leasehold improvements and rent holidays, are capitalized and are recognized as reductions to rental expense on a straight-line basis over the term of the lease. Impairment of Long-Lived Assets Long-lived assets, such as property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated undiscounted future cash flows, an impairment charge is recognized as the amount by which the carrying amount of the asset exceeds the estimated fair value of the asset. As of December 31, 2020 and 2019, no revision to the remaining useful lives or write-down of long-lived assets was required. Income Taxes Income taxes are accounted for under the liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to the differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and the operating loss and tax credit carryforwards. Valuation allowances are established when necessary to reduce deferred tax assets to the amount expected to be realized. Deferred tax assets and liabilities are measured at the balance sheet date using the enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the period such tax rate changes are enacted. Revenue Recognition On January 1, 2019, the Company adopted Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers (Topic 606), and subsequent amendments, using the modified retrospective transition method applied to those contracts that were not completed as of January 1, 2019. As a result, the Company recorded an increase of $6.2 million in each of its accumulated deficit and contract liabilities balances on January 1, 2019. Results for operating periods beginning after January 1, 2019 are presented under ASC 606, while amounts prior to 2019 have not been adjusted and may not be comparable. ASC 606 requires an entity to recognize revenue upon the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The Company applies the following five-step revenue recognition model outlined in ASC 606 to adhere to this core principle: (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when (or as) the Company satisfies a performance obligation. The most significant change to the Company’s policies upon the adoption of ASC 606 was the estimation of an arrangement’s total transaction price, which includes unconstrained All of the Company’s revenue to date has been generated from its collaboration agreements, primarily its collaboration agreement with Merck. The terms of these agreements generally require the Company to provide (i) license options for its compounds, (ii) research and development services and (iii) non-mandatory services in connection with participation in research or steering committees. Payments received under these arrangements may include non-refundable upfront license fees, partial or complete reimbursement of research and development costs, contingent consideration payments based on the achievement of defined collaboration objectives and royalties on sales of commercialized products. In some agreements, the collaboration partner is solely responsible for meeting defined objectives that trigger contingent or royalty payments. Often the partner only pursues such objectives subsequent to exercising an optional license on compounds identified as a result of the research and development services performed under the collaboration agreement. The Company assesses whether the promises in its arrangements, including any options provided to the partner, are considered distinct performance obligations that should be accounted for separately. Judgment is required to determine whether the license to a compound is distinct from research and development services or participation in research or steering committees, as well as whether options create material rights in the contract. The transaction price in each arrangement is generally comprised of a non-refundable upfront fee and unconstrained variable consideration related to the performance of research and development services. The Company typically submits a budget for the research and development services to the partner in advance of performing the services. The transaction price is allocated to the identified performance obligations based on the standalone selling price, or SSP, of each distinct performance obligation. Judgment is required to determine the SSP. In instances where the SSP is not directly observable, such as when a license or service is not sold separately, SSP is determined using information that may include market conditions and other observable inputs. The Company utilizes judgment to assess the nature of its performance obligations to determine whether they are satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress toward completion. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The Company’s collaboration agreements may include contingent payments related to specified development and regulatory milestones or contingent payments for royalties based on sales of a commercialized product. Milestones can be achieved for such activities in connection with progress in clinical trials, regulatory filings in various geographical markets and marketing approvals from regulatory authorities. Sales-based royalties are generally related to the volume of annual sales of a commercialized product. At the inception of each agreement that includes such payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price by using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s or its partner’s control, such as those related to regulatory approvals, are not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation based on a relative SSP basis. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of each such milestone and any related constraint and, if necessary, adjusts its estimate of the overall transaction price. Pursuant to the guidance in ASC 606, sales-based royalties are not included in the transaction price. Instead, royalties are recognized at the later of when the performance obligation is satisfied or partially satisfied, or when the sale that gives rise to the royalty occurs. Research and Development Research and development costs are expensed as incurred. Research and development expenses primarily include salaries and benefits for medical, clinical, quality, preclinical, manufacturing and research personnel, costs related to research activities, preclinical studies, clinical trials, drug manufacturing expenses and allocated overhead and facility occupancy costs. The Company accounts for non-refundable advance payments for goods or services that will be used in future research and development activities as expenses when the goods have been received or when the service has been performed rather than when the payment is made. Clinical trial costs are a component of research and development expenses. The Company expenses costs for its clinical trial activities performed by third parties, including clinical research organizations, or CROs, and other service providers, as they are incurred, based upon estimates of the work completed over the life of the individual study in accordance with associated agreements. The Company uses assessments by internal personnel and information it receives from outside service providers to estimate the clinical trial costs incurred. Stock-Based Compensation The Company’s stock-based compensation programs include stock option grants, as well as shares issued under its 2019 Employee Stock Purchase Plan, or ESPP. Grants are awarded to employees, directors and nonemployees. The Company measures employee and director stock-based compensation expense for all stock-based awards at the grant date based on the fair value measurement of the award. Subsequent to the adoption of ASU No. 2018-07, Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting on January 1, 2019, stock-based compensation expense for non-employee awards is measured based on the fair value on the date of adoption. The expense is recorded on a straight-line basis over the requisite service period, which is generally the vesting period, for the entire award. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures materially differ from estimates. The Company calculates the fair value measurement of stock options using the Black-Scholes option-pricing model. Foreign Currency Transactions The functional currency of NGM Biopharmaceuticals Australia Pty Ltd., the Company’s wholly-owned subsidiary, is the U.S. dollar. Accordingly, all monetary assets and liabilities of the subsidiary are remeasured into U.S. dollars at the current period-end exchange rates and non-monetary assets are remeasured using historical exchange rates. Income and expense elements are remeasured to U.S. dollars using the average exchange rates in effect during the period. Remeasurement gains and losses are recorded as other income (expense), net on the consolidated statements of operations. The Company is subject to foreign currency risk with respect to its clinical and manufacturing contracts denominated in currencies other than the U.S. dollar, primarily British Pounds, Swiss Francs, Australian dollars and the Euro. Payments on contracts denominated in foreign currencies are made at the spot rate on the day of payment. Changes in the exchange rate between billing dates and payment dates are recorded within other income (expense), net, on the consolidated statements of operations. Comprehensive Loss Comprehensive loss is composed of net loss and certain changes in stockholders’ equity (deficit) that are excluded from net loss, primarily unrealized gains or losses, net of taxes, on the Company’s marketable securities. Net Loss per Share Basic net loss per share is calculated by dividing net loss by the weighted average number of shares outstanding during the period, less shares subject to repurchase and excludes any dilutive effects of stock-based options and awards. Diluted net income per ordinary share is computed by giving effect to all potentially dilutive shares, including common stock issuable upon exercise of stock options. However, where there is a diluted net loss per ordinary share, no adjustment is made for potentially issuable shares since their effect would be anti-dilutive. In this case, diluted net loss per share is equal to basic net loss per share. Net loss per share were computed as follows (in thousands, except share and per share amounts): Year Ended December 31, 2020 2019 2018 Numerator: Net loss $ (102,487 ) $ (42,795 ) $ (493 ) Denominator: Weighted average number of shares used in calculating net loss per share—basic and diluted 68,475,378 50,297,524 6,383,751 Net loss per share—basic and diluted $ (1.50 ) $ (0.85 ) $ (0.08 ) Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: Year Ended December 31, 2020 2019 2018 Convertible preferred stock — — 47,267,466 Options to purchase common stock 10,017,918 10,824,780 9,806,689 Shares committed under ESPP 291,992 396,682 - Warrants to purchase convertible preferred stock — — 19,637 Total 10,309,910 11,221,462 57,093,792 Segment and Geographical Information The Company operates in one segment. Substantially all of the Company’s long-lived assets, primarily comprised of property and equipment, are based in the U.S. For the years ended December 31, 2020, 2019 and 2018, the Company’s revenues were entirely within the U.S. Recent Accounting Pronouncements New accounting pronouncements are issued by the Financial Accounting Standards Board, or FASB, or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s results of operations and financial position upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended, the JOBS Act, the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. Recently Adopted Accounting Pronouncements In August 2018, the FASB issued ASU 2018-13, Fair Value Measurements (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, as part of the FASB’s disclosure framework project. ASU 2018-13 modifies the disclosure requirements on fair value measurements in Topic 820, Fair Value Measurements by removing the requirement to disclose amounts of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, the policy for timing of transfers between levels and the valuation process for Level 3 fair value measurements. ASU 2018-13 also modifies existing disclosure requirements by clarifying that the measurement uncertainty disclosure is to communicate information about the uncertainty in measurement as of the reporting date, and adds required disclosures for the changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. The Company adopted ASU 2018-13 effective January 1, 2020, noting no material impact on the Company’s results of operations and financial position. Recent Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which increases lease transparency and comparability among organizations. Under the new standard, lessees will be required to recognize right-of-use, or ROU, assets and lease liabilities arising from lease arrangements on the consolidated balance sheets, with the exception of leases with a term of twelve months or less, which permits a lessee to make an accounting policy election by class of underlying asset not to recognize the ROU assets and lease liabilities. In March 2018, the FASB approved an alternative transition method to the modified retrospective approach, which eliminates the requirement to restate prior period financial statements and allows the cumulative effect of the retrospective allocation to be recorded as an adjustment to the opening balance of retained earnings at the date of adoption. In November 2019, the FASB issued ASU 2019-10, which deferred the effective date for certain ASUs including ASU 2016-02. In June 2020, due to the evolving impacts of the COVID-19 pandemic, the FASB issued ASU 2020-05, which further defers the effective date of ASU 2016-02 which is now effective for the Company’s fiscal year beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. The Company plans to adopt the new lease standard in the fiscal year beginning January 1, 2022, using the optional transition method, which allows the Company to recognize a cumulative-effect adjustment to the opening balance of accumulated deficit at the date of adoption and apply the new disclosure requirements beginning in the period of adoption. The Company also plans to elect the package of practical expedients permitted under the transition guidance within the new standard, which, among other things, allows the Company to carryforward the historical lease classification and make an accounting policy election whereby ROU assets and lease liabilities associated with lease arrangements with terms less than one year will not be recognized. The Company continues to evaluate the impact of this new lease standard to its results of operations and financial position. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (ASC 808): Clarifying the Interaction between ASC 808 and ASC 606, which clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all the guidance in ASC 606 should be applied, including recognition, measurement and presentation and disclosure requirements. ASU 2018-18 adds unit-of-account guidance in ASC 808 to align with the guidance in ASC 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of ASC 606, and requires that in a transaction with a collaborative arrangement participant that is not directly related to sales to third parties, presenting the transaction together with revenue recognized under ASC 606 is precluded if the collaborative arrangement participant is not a customer. ASU 2018-18 will be effective for the Company’s fiscal year beginning after December 15, 2020, and interim periods within fiscal years beginning after December 15, 2021. The Company is currently assessing the timing of adoption and the impact that the adoption of ASU 2018-18 will have on its results of operations and financial position. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The new guidance modifies ASC 740 to simplify several aspects of accounting for income taxes, including eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation. ASU 2019-12 will be effective for the Company for its fiscal year beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022, and is required to be adopted prospectively, with the exception of certain specific amendments. The Company is currently assessing the timing of adoption and the impact that the adoption of ASU 2019 ‑

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements Cash and cash equivalents and marketable securities, all of which are classified as available-for-sale securities, consisted of the following (in thousands): Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value As of December 31, 2020 Money market funds $ 137,658 $ — $ — $ 137,658 U.S. government agencies securities 98,647 9 (3 ) 98,653 Commercial paper 41,945 — — 41,945 Corporate and agency bonds 7,543 — (2 ) 7,541 Totals $ 285,793 $ 9 $ (5 ) $ 285,797 Classified as: Cash and cash equivalents $ 137,658 Short-term marketable securities (amortized cost of $148,135) 148,139 Total $ 285,797 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value As of December 31, 2019 Money market funds $ 244,973 $ — $ — $ 244,973 Corporate and agency bonds 66,063 28 (14 ) 66,077 Commercial paper 24,840 — — 24,840 U.S. government agencies securities 7,985 11 — 7,996 Totals $ 343,861 $ 39 $ (14 ) $ 343,886 Classified as: Cash and cash equivalents $ 244,973 Short-term marketable securities (amortized cost of $98,888) 98,913 Total $ 343,886 Cash and cash equivalents in the table above excludes cash on deposit with banks of $9.4 million and $0.6 million as of December 31, 2020 and 2019, respectively. To date, the Company has not recorded any impairment charges against the market value of its marketable securities. In determining whether a decline is other than temporary, the Company considers various factors including the length of time and extent to which the market value has been less than cost, the financial condition and near-term prospects of the issuer and the Company’s intent and ability to retain its investment in the issuer for a period of time sufficient to allow for any anticipated recovery in market value. As of December 31, 2020 and 2019, the Company’s marketable securities had remaining contractual maturities of less than one year. As of December 31, 2020, there was one marketable security in an unrealized loss position compared to four marketable securities in unrealized loss positions as of December 31, 2019. Marketable securities that had been in unrealized loss positions as of December 31, 2020 and 2019 had been in an unrealized loss position for less than 12 months. The Company does not intend to sell marketable securities that are in an unrealized loss position and it is highly unlikely that the Company will be required to sell the investments before recovery of their amortized cost basis, which may be maturity. Assets and Liabilities Measured at Fair Value on a Recurring Basis The following table summarizes, by major security type, our available-for-sale securities that were measured at fair value on a recurring basis and were categorized using the fair value hierarchy (in thousands): Fair Value Measurements As of December 31, 2020 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 137,658 $ — $ — $ 137,658 U.S. government agencies securities — 98,653 — 98,653 Commercial paper — 41,945 — 41,945 Corporate and agency bonds — 7,541 — 7,541 Totals $ 137,658 $ 148,139 $ — $ 285,797 Fair Value Measurements As of December 31, 2019 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 244,973 $ — $ — $ 244,973 Corporate and agency bonds — 66,077 — 66,077 Commercial paper — 24,840 — 24,840 U.S. government agencies securities — 7,996 — 7,996 Totals $ 244,973 $ 98,913 $ — $ 343,886 The carrying amounts of cash and cash equivalents, the related party receivable and contract asset from collaboration and other current assets and liabilities approximate their respective fair values due to their short-term nature. The Company estimates the fair values of investments in corporate agency bond securities, commercial paper and government agencies securities using Level 2 inputs by taking into consideration valuations obtained from third-party pricing services. There were no transfers of assets or liabilities between the fair value measurement levels during the years ended December 31, 2020 and 2019.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Balance Sheet Components	4. Balance Sheet Components Cash and Restricted Cash A reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets to the amount reported within the consolidated statements of cash flows is as follows (in thousands): December 31, 2020 2019 Cash and cash equivalents $ 147,017 $ 245,598 Restricted cash 1,499 1,874 Total cash, cash equivalents and restricted cash $ 148,516 $ 247,472 Property and Equipment Property and equipment consisted of the following (in thousands): December 31, 2020 2019 Leasehold improvements $ 25,880 $ 25,880 Laboratory equipment and office furniture 23,638 21,652 Computer equipment 1,271 1,201 Construction-in-progress 48 498 Total property and equipment, gross 50,837 49,231 Less: accumulated depreciation and amortization (36,311 ) (29,756 ) Total property and equipment, net $ 14,526 $ 19,475 Depreciation expense for the years ended December 31, 2020, 2019 and 2018 was approximately $6.6 million, $7.6 million and $7.2 million, respectively. Accrued Liabilities Accrued liabilities consisted of the following (in thousands): December 31, 2020 2019 Clinical trials and research and development costs $ 9,316 $ 11,051 Manufacturing costs 8,297 2,593 Personnel-related costs 8,921 6,446 Accrued expenses 3,411 2,901 Total accrued liabilities $ 29,945 $ 22,991 The Company currently uses third-party contract development and manufacturing organizations or contract manufacturing organizations, which the Company refers to collectively as CMOs, to manufacture and supply all of the raw materials, drug substances and drug products for the Company’s research and development programs, including all the clinical trial materials used in the clinical trials of our clinical-stage product candidates. To date, aldafermin and the Company’s other product candidates have been manufactured by third-party manufacturers solely for preclinical studies and relatively small clinical trials.

Research Collaboration and Lice

Research Collaboration and License Agreements	12 Months Ended
	Dec. 31, 2020
Collaboration And License Agreement Disclosure [Abstract]
Research Collaboration and License Agreements	5. Research Collaboration and License Agreements Merck In 2015, the Company entered into a collaboration agreement with Merck, or the Collaboration Agreement, covering the discovery, development and commercialization of novel therapies across a range of therapeutic areas, including a broad, multi-year drug discovery and early development program financially supported by The Collaboration Agreement contemplated an initial five-year research term, and Merck was granted the unilateral right to extend the research phase of the collaboration for two additional two-year terms. Each extension is considered to be and is accounted for as a separate arrangement, if and when the option is exercised by Merck. Under the terms of the Collaboration Agreement, Merck is required to pay a $20.0 million extension fee each time it elects to exercise its unilateral right to extend the research phase of the collaboration for an additional two-year term. In March 2019, Merck exercised its first option to extend the research phase of the collaboration for two additional years through March 16, 2022. Under the Collaboration Agreement, if and when Merck elects to extend the research phase for an additional two years, the level of funding that Merck will provide to the Company during such extension will be negotiated at the time of the extension, subject to certain minimum and maximum funding limits based on a percentage of the then-existing funding. As part of the two-year extension through March 16, 2022, Merck agreed to continue to fund the Company’s research and development efforts up to $75.0 million each year consistent with the initial five-year term and, in lieu of a $20.0 million extension fee that would have otherwise been payable to the Company, Merck agreed to make additional payments totaling up to $20.0 million in support of the Company’s research and development program activities during 2021 and in the first quarter of 2022. Under the terms of the collaboration, Merck was required to notify the Company no later than March 17, 2021 of its unilateral decision whether to exercise its option to extend the research phase of the collaboration for an additional two-year term through March 16, 2024. In March 2021, Merck initiated discussions with the Company with respect to elements of the ongoing collaboration that might be optimized to better address the evolving interests and priorities of both the Company and Merck during the remainder of the current research phase through March 16, 2022 and during any extension of the current research phase and any tail period (which tail period is discussed below). In order to allow negotiations to proceed, the parties have agreed to extend the March 17, 2021 deadline for Merck to deliver its extension notification decision until June 30, 2021. See Note 10 for additional information. The Company has determined the scientific direction and areas of therapeutic interest, with input from Merck, and is primarily responsible for the conduct of all research, preclinical and early clinical development activities, through human proof-of-concept trials. The Company has made the final determinations as to which compounds to advance into and through initial clinical trials and which to progress into a human proof-of-concept trial and the design of any such trials, with input from Merck through various governance committees. Upon completion of a human proof-of-concept study for a particular product candidate, regardless of the results of such study, Merck has the one-time option to obtain an exclusive, worldwide license, on specified terms, to that product candidate, as well as to all other molecules that are directed against the same target and that result in the same effect on such target, collectively referred to as a Merck Licensed Program. For each program that Merck licenses, Merck must pay the Company a one-time fee of $20.0 million. If Merck exercises its license option, Merck is responsible, at its own cost, for any further development and any commercialization activities for compounds within the applicable Merck Licensed Program, subject to the Company’s options to cost and profit share worldwide, and to co-detail those compounds in the United States. Where the Company exercises such an option, the compound is referred to as an NGM Optioned Product. If the Company elects to enter into a cost and profit share on an NGM Optioned Product, Merck has agreed to advance to the Company and/or assume up to 25% of the Company’s share of the global development costs, subject to an aggregate cap over the course of the collaboration. All amounts advanced or assumed accrue interest and would be recouped by Merck in full out of the Company’s share of any profits resulting from sales of the NGM Optioned Product before the Company is entitled to receive any of those profits. If the Company does not elect to enter into a cost and profit-sharing arrangement for a compound it has licensed to Merck, the Company is eligible to receive an aggregate of up to $449.0 million in pre-commercial milestone payments upon the achievement of specific clinical development and regulatory events with respect to the licensed compound for the first three indications in the United States, European Union, or EU, and Japan. The Company is also eligible to receive commercial milestone payments of up to $125.0 million and to receive royalties at ascending low-double digit to mid-teen percentage rates, depending on the level of net sales Merck achieves worldwide for each licensed compound. Under the Collaboration Agreement, the Company also granted Merck a worldwide, exclusive right to conduct research and development on, and to manufacture, use and commercialize, small molecule compounds identified or developed by Merck that have specified activity against any target that the Company is researching or developing under the research phase of the collaboration and that, but for use of the Company’s confidential and proprietary information, Merck would not have discovered. If Merck ultimately does not exercise its license option to a collaboration compound the Company has taken through a human proof-of-concept study that is directed to any such target, Merck’s research license for its own small molecule program with respect to such target will become non-exclusive, but it will retain an exclusive license to any small molecule compounds that it has, as of that time, identified and developed. Merck has sole responsibility for research and development of any of these small molecule compounds, at its own cost. The Company is eligible to receive milestone and royalty payments on small molecule compounds that are developed by Merck under such a license from the Company, in some cases at the same rates as those the Company is eligible to receive from Merck for a Merck Licensed Program originating from the Company’s own research and development efforts, provided that, but for use of the Company’s confidential and proprietary information, Merck would not have discovered such small molecule compounds. However, the Company will not have the option to cost and profit share or the option to co-detail those small molecule products. During the three-month period before the end of the research phase, Merck has the right to review the Company’s then-existing programs and to elect to designate one or more such programs for which the Company will be required to continue to conduct research and development for up to three years, referred to as the tail period. Merck will pay all of the Company’s internal and external costs for its work on such Merck-designated programs, up to certain funding caps that decrease over the tail period and are each a specified percentage of certain funding actually provided to the Company by Merck during the last 12 months of the research phase. Merck also has the right to take over such Merck-designated programs and conduct such research and development activities itself or in partnership with a third party, at its own cost, or to terminate the tail period after a specified notice period. If Merck terminates the tail period, it has the right to elect to transition to itself or a third-party partner, at its own cost, any clinical trials that are then being conducted in such Merck-designated programs. If the Company completes a human proof-of-concept trial in one of such Merck-designated programs during the tail period or if Merck or its third-party partner completes a human proof-of-concept trial in one of such Merck-designated programs during or after the tail period, then Merck will have a one-time right to exercise its option to an exclusive, worldwide license for the collaboration product candidate tested in the proof-of-concept trial and certain related molecules in that program. Merck will lose its option rights at the end of the tail period with respect to all programs for which no collaboration product candidate has completed a human proof-of-concept trial by such time, except for Merck-designated programs that Merck is continuing to use commercially reasonable efforts to research and develop. The Company evaluated the Collaboration Agreement with Merck under ASC 606. The Company identified the following promised goods or services at the inception of the Collaboration Agreement: (i) license to GDF15 receptor agonist program; (ii) license to pursue research and development and commercialization of small molecule compounds; (iii) performance of research and development services for five years; (iv) two options to extend performance of the research and development services, each for two additional years; and (v) options to obtain licenses to additional compounds after proof-of-concept trials. The Company determined the GDF15 receptor agonist program license and small molecule program license are not distinct from the research and development services, resulting in these items being combined into a single performance obligation. The Company considered whether the options created material rights in the contract and concluded that the fee attached to the exercise of such options approximated the SSP of the promised goods or services included in the options. Therefore, the options do not give rise to material rights, are not performance obligations in the Collaboration Agreement and, if and when exercised, will be accounted for as separate arrangements under ASC 606. Additionally, if a separate arrangement is created by the exercise of an option, such amounts would then be contingent on events outside of either party’s control, such as products proving to be commercially viable and governmental agencies granting regulatory approval. Such contingencies and uncertainties result in the amounts being constrained and withheld from inclusion in the estimated transaction price of a separate arrangement. Consequently, the estimated transaction price related to the Collaboration Agreement is comprised of the up-front payment and the ongoing research and development reimbursements. Any fees associated with options, including upfront fees, funding fees and milestones, are not included in the transaction price as they are associated with options that are not material rights and, thus, are not performance obligations within the Collaboration Agreement. For example, in November 2018, Merck exercised its option for a license to further research and develop MK-3655 and other FGFR1c/KLB agonists and paid the Company a $20.0 million fee. The $20.0 million license fee for MK-3655 was not included in the transaction price and was instead recognized in the period of exercise in the fourth quarter of 2018 as the Company had no further obligation related to that license. The Phase 3 clinical study for MK-3655 has not begun, and the Company has not made an election as to whether it will participate in the cost and profit share or receive milestone and royalty payments. The amounts do not impact the estimated transaction price associated with the single performance obligation identified in the Collaboration Agreement. The transaction price associated with the initial five-year term of the Collaboration Agreement consisted of the $94.0 million upfront fee and the funding amounts of up to $75.0 million per year for each of the first five years of the Collaboration Agreement. No milestones or other forms of consideration were included in the transaction price as those amounts are contingent upon Merck exercising an option for licenses on additional compounds and would, therefore, be pursuant to separate arrangements and were not part of the Collaboration Agreement estimated transaction price. As there was only one performance obligation in the Collaboration Agreement, the transaction price was allocated entirely to that performance obligation. At the end of the initial five-year term of the Collaboration Agreement, the remaining contract liability amount of $4.9 million related to the upfront license fee included within the transaction price as of December 31, 2019 was fully earned and recognized during the three months ended March 31, 2020. The Company has fully recognized revenue of approximately $388.1 million related to the single performance obligation associated with the initial five-year term of the Collaboration Agreement. Upon Merck exercising its option to extend the research phase of the collaboration through March 16, 2022, the Company deemed that a separate arrangement containing a distinct two-year performance obligation to provide distinct research and development services was created on March 17, 2020 in accordance with ASC 606. The transaction price of $170.0 million for this two-year performance obligation consists of the potential funding amounts of up to $75.0 million per year plus the additional funding amount of $20.0 million to be made during 2021 and in the first quarter of 2022 if the Company exceeds the $75.0 million funding cap. The Company also uses a cost-based input method to calculate the corresponding amount of revenue to recognize. In applying the cost-based input measure of revenue recognition, the Company measures actual costs incurred relative to budgeted costs to fulfill this distinct two-year performance obligation. These costs consist of full-time equivalent hours plus allowable external (third-party) costs incurred. Revenue is recognized based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligation applied to the transaction price. The Company re-evaluates the estimate of expected costs to satisfy the performance obligation each reporting period and makes adjustments for any significant changes. In addition, the Company also considers any necessary adjustments in an effort to ensure that the transaction price is within the range of potential funding amounts as described above. As such, management applies considerable judgment in estimating expected costs as such costs are key inputs when applying the cost-based input method. As the Company’s estimated measure of progress is updated at each reporting period and revenue is recognized on a cumulative catch-up basis, a significant change in the estimate of expected costs for the remainder of the contract term could have a material impact on revenue recognized (including the possible reversal of previously recognized revenue) at each reporting period, as well as the related impact on contract assets and liabilities. Since the transaction price includes an additional funding amount of $20.0 million to be made during 2021 and in the first quarter of 2022, the timing of when the revenue is recognized for this additional funding amount for performance of the services and when this additional funding amount can be billed resulted in the recognition of a related party contract asset, at December 31, 2020, of $6.1 million. As of December 31, 2019, the Company reported contract liabilities related to the single performance obligation in the Collaboration Agreement of $4.9 million. Of the amount recognized for the adoption of ASC 606 in the reporting period ended December 31, 2019, $6.2 million was included in contract liabilities at the end of the prior reporting period. In connection with the Series E convertible preferred stock purchase agreement, the Company and Merck entered into an agreement whereby Merck agreed to purchase 4,121,683 shares of the Company’s common stock in a separate private placement concurrent with the completion of the Company’s IPO at a price per share equal to the public offering price of $16.00, resulting in Merck owning approximately 19.9% of the Company’s outstanding shares of common stock following the completion of the IPO. A breakout of the milestone payments in connection with the potential achievement of certain clinical development events is as follows (in thousands): First Indication Second Indication Third Indication Upon administration of an applicable product to the first patient in the first Phase 3 clinical trial for such product for the given indication $ 35,000 $ 25,250 $ 17,500 A breakout of the milestone payments in connection with the potential achievement of various regulatory events for each of the three indications, for each of the three geographic areas, is as follows (in thousands): First Indication Second Indication Third Indication Total United States $ 75,000 $ 56,250 $ 37,500 $ 168,750 European Union 60,000 45,000 30,000 135,000 Japan 30,000 22,500 15,000 67,500 $ 165,000 $ 123,750 $ 82,500 $ 371,250 Summary of Collaboration Revenue The Company recognized revenue from its collaboration and license agreements as follows (in thousands): Year Ended December 31, 2020 2019 2018 Related party revenue $ 87,368 $ 103,544 $ 108,665 For the year ended December 31, 2020, the Company recognized collaboration and license revenue under the Collaboration Agreement of $87.4 million primarily related to reimbursable research and development activities, including $61.8 million associated with the performance obligation for the two-year extension period, and $4.9 million related to collaboration and license revenue earned under the initial five-year term that ended in March 2020. Revenue recognized related to the reimbursable research and development activities were recognized using the cost-based input model related to research and development activities. For the year ended December 31, 2019, the Company recognized collaboration and license revenue under the Collaboration Agreement of $103.5 million, of which $24.0 million For the year ended December 31, 2018, the Company recognized collaboration and license revenue under the Collaboration Agreement of $108.7 million, which was comprised of $18.8 million of amortized upfront payments, $20.0 million related to the licensing of MK-3655 and the remaining balance related to research and develop activities reimbursed by Merck provided under the Collaboration Agreement. Related Party Contract Assets and Liabilities Amounts received prior to satisfying the revenue recognition criteria are recorded as contract liabilities in the Company’s consolidated balance sheets. If the related performance obligation is expected to be satisfied within the next twelve months, the contract liability will be classified in current liabilities. Amounts recognized as revenue prior to the Company having an unconditional right (other than a right that is conditioned only on the passage of time) to receipt are recorded as contract assets in the Company's consolidated balance sheets. If the Company expects to have an unconditional right to receive the consideration in the next twelve months, the contract asset will be classified in current assets. Changes in contract liabilities were as follows (in thousands): Amounts Balance at December 31, 2018 $ 22,967 Adoption of ASC 606 6,156 Balance at January 1, 2019 29,123 Revenue recognized included in the contract liability balance at the beginning of the period (24,251 ) Balance at December 31, 2019 4,872 Revenue recognized through March 16, 2020 (4,872 ) Balance at December 31, 2020 $ - As of December 31, 2020, the Company recorded a related party contract asset of $6.1 million related to the portion of revenue recognized prior to having an unconditional right to receipt under the Company’s Collaboration Agreement with Merck.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Operating Lease In December 2015, the Company entered into an operating lease for its corporate office space and laboratory facility at 333 Oyster Point Blvd, South San Francisco, California for approximately 122,000 square feet that expires in December 2023. The lease provided a tenant improvement allowance of $15.2 million that the Company used in 2016 towards $22.3 million in total leasehold improvements that are amortized over the lease term of seven years. The 333 Oyster Point lease agreement required a letter of credit in the amount of $2.3 million as a security deposit to the lease, which the Company has recorded as non-current restricted cash on the consolidated balance sheets. The Company has the right to reduce the letter of credit amount by $0.4 million on each of the third anniversary and fourth anniversary of the rent commencement date. For the year ended December 31, 2020, the Company reduced its letter of credit by $0.4 million and reclassified that amount from restricted cash to cash and cash equivalents on the consolidated balance sheets. In September 2009, the Company entered into an operating lease for a corporate office space and laboratory facility at 630 Gateway Blvd, in South San Francisco, California for approximately 50,000 square feet, as amended in June 2014. In July 2016, the Company assigned the operating lease of 630 Gateway to Merck, as part of the Company’s relocation to 333 Oyster Point. The operating lease expired in November 2020. Following expiration of the operating lease, the Company retains the obligation to indemnify the landlord and Merck under certain limited circumstances, but has no further payment obligations. The Company recognizes rent expense on a straight-line basis over the lease period with the difference recorded as deferred rent. In addition, tenant improvement allowances recorded are amortized as a reduction to rent expense on a straight-line basis over the lease term. Rent expense under these facility operating leases was approximately $2.2 million for the years ended December 31, 2020, 2019 and 2018, respectively. Future minimum payments under the unassigned lease obligations described above are as follows as of December 31, 2020 (in thousands): Year Ended December 31, 2021 $ 5,141 2022 5,294 2023 5,455 Total $ 15,890 Indemnification In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and may provide for indemnification of the counterparty. The Company’s exposure under these agreements is unknown because it involves claims that may be made against it in the future but have not yet been made. In accordance with the Company’s amended and restated certificate of incorporation and its amended and restated bylaws, the Company has indemnification obligations to its officers and directors, subject to some limits, with respect to their service in such capacities. The Company has also entered into indemnification agreements with its directors and certain of its officers. To date, the Company has not been subject to any claims, and it maintains director and officer insurance that may enable it to recover a portion of any amounts paid for future potential claims. The Company’s exposure under these agreements is unknown because it involves claims that may be made against it in the future but have not yet been made. The Company believes that the fair value of these indemnification obligations is minimal and, accordingly, it has not recognized any liabilities relating to these obligations for any period presented.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Stockholders' Equity	7. Stockholders’ Equity Preferred Stock The Company has 10,000,000 shares of preferred stock authorized, which may be issued at the discretion of the Company’s board of directors. The board of directors may issue shares of preferred stock in one or more series and to fix the number, rights, preferences, privileges and restrictions. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences and sinking fund terms. As of December 31, 2020, the Company does not have any shares of preferred stock issued or outstanding. Common Stock As of December 31, 2020 and 2019, the Company had 70,585,364 and 66,960,279 shares of common stock outstanding, respectively, which included shares subject to repurchase of 6,508 and 74,454, respectively, as a result of early exercise of stock options not yet vested. The Company had reserved the following shares of common stock for issuance: December 31, 2020 2019 Reserve balance for Sales Agreement 14,190,300 - Common stock options outstanding 10,017,918 10,824,780 Common stock options available for grant 6,186,497 5,316,066 ESPP shares available for purchase 700,074 897,255 401(k) matching plan 21,930 28,274 Total 31,116,719 17,066,375 Open Market Sale Agreement In June 2020, the Company entered into the Sales Agreement with Jefferies relating to the sale of shares of its common stock. In accordance with the terms of the Sales Agreement, the Company may offer and sell shares of its common stock having an aggregate offering price of up to $150.0 million from time to time through Jefferies acting as its sales agent. In December 2020, under the Sales Agreement, the Company sold 809,700 shares of its common stock at an average price of $27.94 per share for net proceeds of $21.9 million, after deducting $0.7 million in sales commissions. In with connection with the transaction, the Company reclassified $0.6 million in deferred offering cost from other assets to equity. As of December 31, 2020, $127.4 million of the Company’s common stock remained available to be sold under the Sales Agreement, subject to certain conditions as specified in the Sales Agreement. Stock Option Plan In 2018, the Company adopted the 2018 Equity Incentive Plan, or 2018 Plan, for eligible employees, officers, directors, advisors and consultants, which provides for the grant of incentive and non-statutory stock options, restricted stock awards and stock appreciation rights. The terms of the stock option agreements, including vesting requirements, are determined by the board of directors, subject to the provisions of the 2018 Plan. Options granted by the Company generally vest within four years and are exercisable from the grant date until ten years after the date of grant. Vesting of certain employee options may be accelerated in the event of a change in control of the Company. As of December 31, 2020, 17,874,624 shares of common stock had been authorized for issuance under the 2018 Plan. Pursuant to the terms of the 2018 Plan, the number of shares reserved and available to issue will automatically increase on January 1st of each year in an amount equal to 4% of the total number of common shares outstanding on the December 31st immediately preceding calendar year, unless the board of directors elects to forego or reduce such increase. The Company’s 2008 Equity Incentive Plan expired at the beginning of 2018. Stock options are governed by stock option agreements between the Company and recipients of stock options. Prior to the closing of the Company’s IPO, the board of directors exercised reasonable judgment and considered a number of objective and subjective factors to determine the best estimate of the fair value of the Company’s common stock, including the Company’s stage of development; progress of its research and development efforts; the rights, preferences and privileges of its convertible preferred stock relative to those of its common stock; equity market conditions affecting comparable companies; and the lack of marketability of the Company’s common stock. Subsequent to the IPO, the exercise price of each option may not be less than 100% of the fair market value of the common stock subject to the option on the date the option is granted. A 10% or greater stockholder may not be granted an incentive stock option unless the exercise price of such option is at least 110% of the fair value of the common stock on the date of grant and the option is not exercisable after the expiration of five years from the grant date. Options become exercisable and expire as determined by the Compensation Committee of the Company’s board of directors, provided that the term of incentive stock options may not exceed ten years from the date of grant for options granted to those other than 10% stockholders. 2019 Employee Stock Purchase Plan Stock Option Activity A summary of the outstanding stock options is as follows: Outstanding Options Options Available for Grant Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Life (in Years) Aggregate Intrinsic Value (in Thousands) Balances at December 31, 2019 5,316,066 10,824,780 $ 7.52 6.29 $ 118,770 Additional shares reserved 2,678,411 Options granted (2,576,501 ) 2,576,501 17.62 Options exercised — (2,614,842 ) 4.53 Options cancelled 768,521 (768,521 ) 12.43 Balances at December 31, 2020 6,186,497 10,017,918 $ 10.52 6.45 $ 198,097 Vested and expected to vest at December 31, 2020 9,872,681 $ 10.44 6.41 $ 196,065 Outstanding and exercisable at December 31, 2020 10,017,918 $ 10.52 6.45 $ 198,097 The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the estimated fair value of the Company’s common stock. Early Exercise of Stock Options The 2018 Plan allows for the granting of options that may be exercised before the options have vested. Shares issued as a result of early exercise that have not vested are subject to repurchase by the Company upon termination of the purchaser’s employment or services, at the price paid by the purchaser, and are not deemed to be issued for accounting purposes until those related shares vest. The amounts received in exchange for these shares have been recorded as a liability on the consolidated balance sheets and will be reclassified into common stock and additional paid-in-capital as the shares vest. The Company’s right to repurchase these shares generally lapses in equal installments over four years beginning from the original vesting commencement date. As of December 31, 2020, there were 6,508 shares of common stock outstanding subject to the Company’s right of repurchase at prices ranging from $7.70 to $8.14 per share. At December 31, 2019, there were 74,454 shares of common stock outstanding subject to the Company’s right of repurchase at prices ranging from $7.64 to $8.14 per share. As of December 31, 2020 and 2019, the Company recorded $0.1 million and $0.6 million, respectively, as early exercise stock option liabilities associated with shares issued with repurchase rights. Employee Stock-Based Compensation Expense Employee and director stock-based compensation expense was calculated based on awards ultimately expected to vest and has been reduced for estimated forfeitures. The Company estimates forfeiture rates based on historical stock option grants and cancellations. Stock-based compensation expense related to Year Ended December 31, 2020 2019 2018 Research and development $ 8,145 $ 7,145 $ 5,232 General and administrative 7,312 5,584 4,524 Total stock-based compensation expense $ 15,457 $ 12,729 $ 9,756 Valuation Assumptions The Company uses the Black-Scholes option-pricing model to estimate the fair value of stock options at the grant date. The Black-Scholes option-pricing model requires the Company to make certain estimates and assumptions, including assumptions related to the expected price volatility of the Company’s stock, the period during which the options will be outstanding, the rate of return on risk-free investments and the expected dividend yield for the Company’s stock. The expected volatility is based on the historical volatility of the stock of similar entities within the Company’s industry over periods commensurate with the Company’s expected term assumption. The expected term of stock option grants represents the weighted-average period the options are expected to remain outstanding and is based on the “simplified” method where the expected term is the midpoint between the vesting date and the end of the contractual term for each option. The Company bases the risk-free interest rate on the interest rate payable on U.S. Treasury securities in effect at the time of grant for a period that is commensurate with the assumed expected option term. In reference to the expected dividend yield assumption, the Company has not historically paid, and does not expect for the foreseeable future to pay, a dividend. The weighted average grant-date fair value of stock options granted during the years ended December 31, 2020, 2019 and 2018 was $10.86, $8.00 and $5.71 per share, respectively. The intrinsic value of stock options exercised was $40.9 million, $10.2 million and $1.9 million for the years ended December 31, 2020, 2019 and 2018, respectively. Due to the Company’s net operating losses, the Company did not realize any tax benefits from stock-based payment arrangements for the year ended December 31, 2020, 2019 and 2018. The fair value of stock option awards granted to employees and directors were estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted average valuation assumptions: Year Ended December 31, 2020 2019 2018 Volatility 68 % 65 % 65 % Expected term (years) 6.23 6.18 5.98 Risk-free interest rate 1.04 % 2.25 % 2.59 % Expected dividend yield — — — As of December 31, 2020, total compensation cost not yet recognized related to unvested stock options granted to employees and directors was $29.6 million, which is expected to be recognized over a weighted-average period of 2.75 years. Stock Options Granted to Certain Non-employees The Company grants stock options to certain non-employees in exchange for services performed for the Company. The Company granted 67,500 and 22,500 options to non-employees for the years ended December 31, 2020 and 2019, respectively. For the year ended December 31, 2018, the Company did not grant any options to non-employees. Stock-based compensation expense related to stock-based payment awards to non-employees for the years ended December 31, 2020, 2019 and 2018 was $194,000, $133,000 and $103,000, respectively. The fair value of stock option awards granted to non-employees was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted average valuation assumptions: Year Ended December 31, 2020 2019 2018 Volatility 70 % 66 % — Expected term (years) 6.02 6.00 — Risk-free interest rate 0.41 % 2.26 % — Expected dividend yield — — — The fair value of the rights granted to employees under the ESPP was estimated at the date of offer using a Black-Scholes option-pricing model with the following weighted average valuation assumptions: Year Ended December 31, 2020 2019 2018 Volatility 74 % 59 % — Expected term (years) 1.17 1.23 — Risk-free interest rate 0.15 % 1.97 % — Expected dividend yield — — —

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plan	8. Employee Benefit Plan The Company sponsors a 401(k) defined contribution plan for its employees. Employee contributions are voluntary. In December 2011, the Company adopted the 401(k) Matching Plan, under which the Company makes matching contributions in the form of common stock at a rate of $1.00 for each $2.00 of employee contributions up to a maximum $750 of common stock per employee per year. As of December 31, 2020 and 2019, the Company had reserved 21,930 and 28,274 shares of common stock for issuance pursuant to the 401(k) Matching Plan, respectively. Matching contributions of 6,344 and 8,477 shares, or $119,000 and $98,000, were issued for the years ended December 31, 2020 and 2019, respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The Company has reported pre-tax operating losses for all periods presented. The Company has not reflected any benefit for corresponding tax net operating loss carryforwards in the accompanying consolidated financial statements. The Company has established a full valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets. The components of the Company’s losses before income taxes were as follows (in thousands): Year Ended December 31, 2020 2019 2018 Domestic $ (102,209 ) $ (34,634 ) $ 5,502 Foreign (278 ) (8,161 ) (5,995 ) Total $ (102,487 ) $ (42,795 ) $ (493 ) A reconciliation of the statutory U.S. federal rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2020 2019 2018 U.S. federal tax at statutory rate 21.0 % 21.0 % 21.0 % Foreign tax rate differential 0.0 1.7 109.5 State, net of federal benefit (0.1 ) 0.0 (4.5 ) Stock-based compensation 3.8 0.2 (93.1 ) Change in valuation allowance (25.0 ) (23.2 ) 401.6 Other 0.3 0.2 (434.7 ) Total 0.0 % 0.0 % (0.2 ) % The components of the net deferred tax assets are as follows (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 60,879 $ 37,679 Stock-based compensation 4,580 3,478 Research and development credit 2,918 2,918 Contract liabilities — 1,026 Other temporary differences 2,079 1,217 Total gross deferred tax assets 70,456 46,318 Deferred tax liabilities: Depreciation and amortization (389 ) (570 ) Non-qualified stock options with 83(b) election (15 ) (15 ) Total gross deferred tax liabilities (404 ) (585 ) Net deferred tax assets before valuation allowance 70,052 45,733 Deferred tax asset valuation allowance (70,052 ) (45,733 ) Net deferred tax assets $ — $ — ASC 740 requires that the tax benefit of net operating losses, temporary differences and credit carryforwards be recorded as an asset to the extent that management assesses that realization is “more likely than not.” Realization of the future tax benefits is dependent on the Company’s ability to generate sufficient taxable income within the carryforward period. Because of the Company’s recent history of operating losses, management believes that recognition of the deferred tax assets arising from the above-mentioned future tax benefits is currently not more-likely-than-not to be realized and, accordingly, has provided a valuation allowance. Realization of deferred tax assets is dependent upon future earnings, if any, the timing and amount of which are uncertain. Accordingly, the net deferred tax assets have been fully offset by a valuation allowance. The valuation allowance increased by approximately $24.3 million and $9.5 million during the years ended December 31, 2020 and 2019, respectively. As of December 31, 2020, the Company had approximately $226.8 million in federal net operating loss carryforwards to reduce future taxable income. Of this amount, $161.4 million was generated after December 31, 2017 and does not expire per the Tax Cuts and JOBS Act, or the 2017 Tax Act, and can be carried forward indefinitely. The federal net operating loss carryforwards generated prior to January 1, 2018 are subject to a 20-year carryforward period and will begin to expire after 2032. Subsequent to the enactment of the 2017 Tax Act, the utilization of the federal net operating loss carryforwards generated in fiscal year 2018 and onwards is limited to 80% of the federal taxable income. The Company also had approximately $145.8 million in state net operating loss carryforwards to reduce future taxable income, which will begin to expire after 2028, if not utilized. The Company had approximately $3.1 million in federal research and development tax credits for each of the years ended December 31, 2020 and 2019. In addition, the Company had approximately $4.0 million in state research and development tax credits for each of the years ended December 31, 2020 and 2019. The federal research credits will begin to expire in the years 2028 through 2035, if not utilized. The state research and development credits have no expiration date and can be carried forward indefinitely. As of December 31, 2020 and 2019, the Company had foreign net operating loss carryforwards of approximately $35.8 million and $29.7 million, respectively, which have no expiration date. Utilization of the Company’s net operating losses and credits may be subject to a substantial annual limitation due to the “change in ownership” provisions of the Internal Revenue Code of 1986, as amended, and similar state provisions. The annual limitation may result in the expiration of net operating losses and credits before utilization. A reconciliation of the Company’s unrecognized tax benefits is as follows (in thousands): December 31, 2020 2019 2018 Balance at beginning of year $ 3,819 $ 3,819 $ 1,528 Additions based on tax positions related to prior year 314 — 2,291 Additions based on tax positions related to current year 6,213 — — Balance at end of year $ 10,346 $ 3,819 $ 3,819 The entire amount of the unrecognized tax benefits would not impact the Company’s effective tax rate if recognized. The Company has elected to include interest and penalties as a component of tax expense. During the years ended December 31, 2020 and 2019, the Company did not recognize accrued interest and penalties related to unrecognized tax benefits. The Company does not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease during the next 12 months. The Company files federal, state and foreign income tax returns with varying statutes of limitations. The tax years from inception in 2008 to December 31, 2019 remain subject to examination. On March 27, 2020, the Coronavirus Aid, Relief and Economic Security Act, or the CARES Act, was enacted. Under U.S. GAAP, the Company is required to recognize the tax effects of new legislation in the reporting period in which the legislation was enacted. The CARES Act included changes to current U.S. tax provisions that benefit business entities and modified certain tax provisions of the 2017 Tax Act. The tax relief measures included a five-year net operating loss carryback, suspension of the annual deduction limitation of 80% of taxable income from net operating losses generated in a tax year beginning after December 31, 2017, changes in the deductibility of interest, acceleration of alternative minimum tax credit refunds, payroll tax relief and a technical correction to allow accelerated deductions for qualified improvement properties. The CARES Act also provided other non-tax benefits to assist business entities impacted by the ongoing COVID-19 pandemic. The Company has evaluated the CARES Act and concluded that it did not result in any material adjustments to the Company’s income tax provision or net deferred tax assets for the year ended December 31, 2020.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Subsequent Events	10. Subsequent Events Public Offering of Common Stock On January 5, 2021, the Company entered into an underwriting agreement with representatives of several underwriters relating to the public offering, issuance and sale of 4,629,630 shares of its common stock. The price to the public in the offering was $27.00 per share. Under the terms of the underwriting agreement, the Company granted the underwriters an option exercisable for 30 days to purchase up to an additional 694,444 shares of common stock at the public offering price, less underwriting discounts and commissions. The underwriters exercised in full their option to purchase the additional shares. The net proceeds to the Company from the offering were approximately $134.7 million, after deducting underwriting discounts and commissions and other estimated offering expenses payable by the Company. The offering closed on January 8, 2021. Merck Collaboration Under the terms of the collaboration, Merck was required to notify the Company no later than March 17, 2021 of its unilateral decision whether to exercise its option to extend the research phase of the collaboration for an additional two-year term through March 16, 2024. The parties are negotiating in good faith certain modifications to the terms of the collaboration and in order to allow negotiations to proceed, the parties have agreed to extend the March 17, 2021 deadline for Merck to deliver its extension notification decision until June 30, 2021.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or U.S. GAAP, and include the consolidated accounts of the Company and its wholly-owned subsidiary in Australia. All intercompany balances and transactions have been eliminated upon consolidation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make judgments, assumptions and estimates that affect the amounts reported in the consolidated financial statements and accompanying notes. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. Actual results could differ materially from those estimates.
Uses and Sources of Liquidity	Uses and Sources of Liquidity Since inception, the Company has incurred net losses and negative cash flow from operations. During the years ended December 31, 2020, 2019 and 2018, the Company incurred net losses of $102.5 million, $42.8 million and $0.5 million, respectively. As of December 31, 2020, the Company had an accumulated deficit of $298.6 million. The Company expects its accumulated deficit will increase significantly over time and does not expect to experience positive cash flows from operations in the near future. In December 2020, under an Open Market Sale Agreement SM As of December 31, 2020, the Company had $295.2 million of cash, cash equivalents and short-term marketable securities. In January 2021, the Company sold 5,324,074 shares of its common stock through an underwritten public offering at a price of $27.00 per share for aggregate net proceeds of approximately $134.7 million after deducting underwriting discounts and commissions and other estimated offering expenses payable by the Company. See Note 10 for additional information. The Company believes that the net proceeds from this offering, together with its existing cash, cash equivalents and short-term marketable securities, will be sufficient to fund its operations for a period of at least one year from the date these consolidated financial statements are issued. To fully implement the Company’s business plan and fund its operations, the Company will need to raise additional capital through public or private equity offerings (which may include potential net proceeds from future sales, if any, under the Sales Agreement), debt financings, government or other third-party funding, collaborations, strategic alliances and licensing arrangements or a combination of the foregoing.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of cash and cash equivalents, the related party receivable from collaboration and other current assets and liabilities approximate their respective fair values due to their short-term nature.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents are stated at fair value. Cash equivalents are securities with an original maturity of three months or less at the time of purchase. The Company limits its credit risk associated with cash and cash equivalents by placing its investments with a bank it believes is highly creditworthy and with highly rated money market funds. As of December 31, 2020 and 2019, cash and cash equivalents consisted of bank deposits and investments in money market funds.
Marketable Securities	Marketable Securities The appropriate classification of the Company’s marketable securities is determined at the time of purchase and such designations are re-evaluated at each balance sheet date. All of the Company’s securities are considered as available-for-sale and carried at estimated fair values and reported in cash equivalents and short-term marketable securities. Unrealized gains and losses on available-for-sale securities are excluded from net loss and reported in accumulated other comprehensive gain as a separate component of stockholders’ equity. Other income (expense), net, includes interest, amortization of purchase premiums and accretion of purchase discounts, realized gains and losses on sales of securities and other-than-temporary declines in the fair value of securities, if any. The cost of securities sold is based on the specific identification method. The Company’s investments are regularly reviewed for other-than-temporary declines in fair value. This review includes the consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether the Company has the intent to sell the securities and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. When the Company determines that the decline in fair value of an investment is below its carrying value and this decline is other-than-temporary, the Company reduces the carrying value of the security it holds and records a loss for the amount of such decline. As of December 31, 2020, the Company did not record any impairment related to other-than-temporary declines in the fair value of securities.
Restricted Cash	Restricted Cash The Company’s restricted cash balance represents collateral required under the Company’s facility lease agreement and is classified as a non-current asset on the consolidated balance sheets, as the collateral will not be returned to the Company in 2021.
Concentration of Credit and Other Risks	Concentration of Credit and Other Risks Cash and cash equivalents and marketable securities from the Company’s available-for-sale and marketable security portfolio potentially subject the Company to concentrations of credit risk. The Company is invested in money market funds and marketable securities through custodial relationships with major U.S. and Australian banks. Under its investment policy, the Company limits amounts invested in such securities by credit rating, maturity, industry group, investment type and issuer, except for securities issued by the U.S. government. Related party receivables from collaborations are typically unsecured. Accordingly, the Company may be exposed to credit risk generally associated with its current collaboration agreement with Merck and any future collaboration agreements with other collaboration partners. To date, the Company has not experienced any losses related to these receivables. Amounts recognized as revenue prior to the Company having an unconditional right (other than a right that is conditioned only on the passage of time) to receipt are recorded as contract assets in the Company's consolidated balance sheets. Although the Company expects to have an unconditional right to receive such amounts, the Company may be exposed to the risk of not receiving the recorded amounts under its current collaboration agreement with Merck and any future collaboration agreements with other collaboration partners. To date, the Company has not experienced any losses related to contract assets. Merck accounted for 100% of the Company’s revenue for the years ended December 31, 2020, 2019 and 2018.
Property and Equipment, Net	Property and Equipment, Net Property and equipment is recorded at cost and consists of computer equipment, laboratory equipment and office furniture and leasehold improvements. Maintenance and repairs, and training on the use of equipment, are expensed as incurred. Costs that improve assets or extend their economic lives are capitalized. Depreciation is recognized using the straight-line method based on an estimated useful life of the asset, which is as follows: Computer equipment 3 years Laboratory equipment and office furniture 3 years Leasehold improvement Shorter of life of asset or lease term
Leases	Leases The Company’s lease agreements for its laboratory and office facilities are classified as operating leases. Rent expense is recognized on a straight-line basis over the term of the lease. Incentives granted under the Company’s facilities leases, including allowances to fund leasehold improvements and rent holidays, are capitalized and are recognized as reductions to rental expense on a straight-line basis over the term of the lease.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets, such as property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the estimated undiscounted future cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated undiscounted future cash flows, an impairment charge is recognized as the amount by which the carrying amount of the asset exceeds the estimated fair value of the asset. As of December 31, 2020 and 2019, no revision to the remaining useful lives or write-down of long-lived assets was required.
Income Taxes	Income Taxes Income taxes are accounted for under the liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to the differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and the operating loss and tax credit carryforwards. Valuation allowances are established when necessary to reduce deferred tax assets to the amount expected to be realized. Deferred tax assets and liabilities are measured at the balance sheet date using the enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the period such tax rate changes are enacted.
Revenue Recognition	Revenue Recognition On January 1, 2019, the Company adopted Accounting Standards Update, or ASU, 2014-09, Revenue from Contracts with Customers (Topic 606), and subsequent amendments, using the modified retrospective transition method applied to those contracts that were not completed as of January 1, 2019. As a result, the Company recorded an increase of $6.2 million in each of its accumulated deficit and contract liabilities balances on January 1, 2019. Results for operating periods beginning after January 1, 2019 are presented under ASC 606, while amounts prior to 2019 have not been adjusted and may not be comparable. ASC 606 requires an entity to recognize revenue upon the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The Company applies the following five-step revenue recognition model outlined in ASC 606 to adhere to this core principle: (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when (or as) the Company satisfies a performance obligation. The most significant change to the Company’s policies upon the adoption of ASC 606 was the estimation of an arrangement’s total transaction price, which includes unconstrained All of the Company’s revenue to date has been generated from its collaboration agreements, primarily its collaboration agreement with Merck. The terms of these agreements generally require the Company to provide (i) license options for its compounds, (ii) research and development services and (iii) non-mandatory services in connection with participation in research or steering committees. Payments received under these arrangements may include non-refundable upfront license fees, partial or complete reimbursement of research and development costs, contingent consideration payments based on the achievement of defined collaboration objectives and royalties on sales of commercialized products. In some agreements, the collaboration partner is solely responsible for meeting defined objectives that trigger contingent or royalty payments. Often the partner only pursues such objectives subsequent to exercising an optional license on compounds identified as a result of the research and development services performed under the collaboration agreement. The Company assesses whether the promises in its arrangements, including any options provided to the partner, are considered distinct performance obligations that should be accounted for separately. Judgment is required to determine whether the license to a compound is distinct from research and development services or participation in research or steering committees, as well as whether options create material rights in the contract. The transaction price in each arrangement is generally comprised of a non-refundable upfront fee and unconstrained variable consideration related to the performance of research and development services. The Company typically submits a budget for the research and development services to the partner in advance of performing the services. The transaction price is allocated to the identified performance obligations based on the standalone selling price, or SSP, of each distinct performance obligation. Judgment is required to determine the SSP. In instances where the SSP is not directly observable, such as when a license or service is not sold separately, SSP is determined using information that may include market conditions and other observable inputs. The Company utilizes judgment to assess the nature of its performance obligations to determine whether they are satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress toward completion. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The Company’s collaboration agreements may include contingent payments related to specified development and regulatory milestones or contingent payments for royalties based on sales of a commercialized product. Milestones can be achieved for such activities in connection with progress in clinical trials, regulatory filings in various geographical markets and marketing approvals from regulatory authorities. Sales-based royalties are generally related to the volume of annual sales of a commercialized product. At the inception of each agreement that includes such payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price by using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s or its partner’s control, such as those related to regulatory approvals, are not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation based on a relative SSP basis. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of each such milestone and any related constraint and, if necessary, adjusts its estimate of the overall transaction price. Pursuant to the guidance in ASC 606, sales-based royalties are not included in the transaction price. Instead, royalties are recognized at the later of when the performance obligation is satisfied or partially satisfied, or when the sale that gives rise to the royalty occurs.
Research and Development	Research and Development Research and development costs are expensed as incurred. Research and development expenses primarily include salaries and benefits for medical, clinical, quality, preclinical, manufacturing and research personnel, costs related to research activities, preclinical studies, clinical trials, drug manufacturing expenses and allocated overhead and facility occupancy costs. The Company accounts for non-refundable advance payments for goods or services that will be used in future research and development activities as expenses when the goods have been received or when the service has been performed rather than when the payment is made. Clinical trial costs are a component of research and development expenses. The Company expenses costs for its clinical trial activities performed by third parties, including clinical research organizations, or CROs, and other service providers, as they are incurred, based upon estimates of the work completed over the life of the individual study in accordance with associated agreements. The Company uses assessments by internal personnel and information it receives from outside service providers to estimate the clinical trial costs incurred.
Stock-Based Compensation	Stock-Based Compensation The Company’s stock-based compensation programs include stock option grants, as well as shares issued under its 2019 Employee Stock Purchase Plan, or ESPP. Grants are awarded to employees, directors and nonemployees. The Company measures employee and director stock-based compensation expense for all stock-based awards at the grant date based on the fair value measurement of the award. Subsequent to the adoption of ASU No. 2018-07, Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting on January 1, 2019, stock-based compensation expense for non-employee awards is measured based on the fair value on the date of adoption. The expense is recorded on a straight-line basis over the requisite service period, which is generally the vesting period, for the entire award. Forfeitures are estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures materially differ from estimates. The Company calculates the fair value measurement of stock options using the Black-Scholes option-pricing model.
Foreign Currency Transactions	Foreign Currency Transactions The functional currency of NGM Biopharmaceuticals Australia Pty Ltd., the Company’s wholly-owned subsidiary, is the U.S. dollar. Accordingly, all monetary assets and liabilities of the subsidiary are remeasured into U.S. dollars at the current period-end exchange rates and non-monetary assets are remeasured using historical exchange rates. Income and expense elements are remeasured to U.S. dollars using the average exchange rates in effect during the period. Remeasurement gains and losses are recorded as other income (expense), net on the consolidated statements of operations. The Company is subject to foreign currency risk with respect to its clinical and manufacturing contracts denominated in currencies other than the U.S. dollar, primarily British Pounds, Swiss Francs, Australian dollars and the Euro. Payments on contracts denominated in foreign currencies are made at the spot rate on the day of payment. Changes in the exchange rate between billing dates and payment dates are recorded within other income (expense), net, on the consolidated statements of operations.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is composed of net loss and certain changes in stockholders’ equity (deficit) that are excluded from net loss, primarily unrealized gains or losses, net of taxes, on the Company’s marketable securities.
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing net loss by the weighted average number of shares outstanding during the period, less shares subject to repurchase and excludes any dilutive effects of stock-based options and awards. Diluted net income per ordinary share is computed by giving effect to all potentially dilutive shares, including common stock issuable upon exercise of stock options. However, where there is a diluted net loss per ordinary share, no adjustment is made for potentially issuable shares since their effect would be anti-dilutive. In this case, diluted net loss per share is equal to basic net loss per share. Net loss per share were computed as follows (in thousands, except share and per share amounts): Year Ended December 31, 2020 2019 2018 Numerator: Net loss $ (102,487 ) $ (42,795 ) $ (493 ) Denominator: Weighted average number of shares used in calculating net loss per share—basic and diluted 68,475,378 50,297,524 6,383,751 Net loss per share—basic and diluted $ (1.50 ) $ (0.85 ) $ (0.08 ) Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: Year Ended December 31, 2020 2019 2018 Convertible preferred stock — — 47,267,466 Options to purchase common stock 10,017,918 10,824,780 9,806,689 Shares committed under ESPP 291,992 396,682 - Warrants to purchase convertible preferred stock — — 19,637 Total 10,309,910 11,221,462 57,093,792
Segment and Geographical Information	Segment and Geographical Information The Company operates in one segment. Substantially all of the Company’s long-lived assets, primarily comprised of property and equipment, are based in the U.S. For the years ended December 31, 2020, 2019 and 2018, the Company’s revenues were entirely within the U.S.
Recent Accounting Pronouncements	Recent Accounting Pronouncements New accounting pronouncements are issued by the Financial Accounting Standards Board, or FASB, or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company’s results of operations and financial position upon adoption. Under the Jumpstart Our Business Startups Act of 2012, as amended, the JOBS Act, the Company meets the definition of an emerging growth company and has elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act. Recently Adopted Accounting Pronouncements In August 2018, the FASB issued ASU 2018-13, Fair Value Measurements (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, as part of the FASB’s disclosure framework project. ASU 2018-13 modifies the disclosure requirements on fair value measurements in Topic 820, Fair Value Measurements by removing the requirement to disclose amounts of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, the policy for timing of transfers between levels and the valuation process for Level 3 fair value measurements. ASU 2018-13 also modifies existing disclosure requirements by clarifying that the measurement uncertainty disclosure is to communicate information about the uncertainty in measurement as of the reporting date, and adds required disclosures for the changes in unrealized gains and losses for the period included in other comprehensive income for recurring Level 3 fair value measurements held at the end of the reporting period and the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements. The Company adopted ASU 2018-13 effective January 1, 2020, noting no material impact on the Company’s results of operations and financial position. Recent Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which increases lease transparency and comparability among organizations. Under the new standard, lessees will be required to recognize right-of-use, or ROU, assets and lease liabilities arising from lease arrangements on the consolidated balance sheets, with the exception of leases with a term of twelve months or less, which permits a lessee to make an accounting policy election by class of underlying asset not to recognize the ROU assets and lease liabilities. In March 2018, the FASB approved an alternative transition method to the modified retrospective approach, which eliminates the requirement to restate prior period financial statements and allows the cumulative effect of the retrospective allocation to be recorded as an adjustment to the opening balance of retained earnings at the date of adoption. In November 2019, the FASB issued ASU 2019-10, which deferred the effective date for certain ASUs including ASU 2016-02. In June 2020, due to the evolving impacts of the COVID-19 pandemic, the FASB issued ASU 2020-05, which further defers the effective date of ASU 2016-02 which is now effective for the Company’s fiscal year beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. The Company plans to adopt the new lease standard in the fiscal year beginning January 1, 2022, using the optional transition method, which allows the Company to recognize a cumulative-effect adjustment to the opening balance of accumulated deficit at the date of adoption and apply the new disclosure requirements beginning in the period of adoption. The Company also plans to elect the package of practical expedients permitted under the transition guidance within the new standard, which, among other things, allows the Company to carryforward the historical lease classification and make an accounting policy election whereby ROU assets and lease liabilities associated with lease arrangements with terms less than one year will not be recognized. The Company continues to evaluate the impact of this new lease standard to its results of operations and financial position. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (ASC 808): Clarifying the Interaction between ASC 808 and ASC 606, which clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all the guidance in ASC 606 should be applied, including recognition, measurement and presentation and disclosure requirements. ASU 2018-18 adds unit-of-account guidance in ASC 808 to align with the guidance in ASC 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of ASC 606, and requires that in a transaction with a collaborative arrangement participant that is not directly related to sales to third parties, presenting the transaction together with revenue recognized under ASC 606 is precluded if the collaborative arrangement participant is not a customer. ASU 2018-18 will be effective for the Company’s fiscal year beginning after December 15, 2020, and interim periods within fiscal years beginning after December 15, 2021. The Company is currently assessing the timing of adoption and the impact that the adoption of ASU 2018-18 will have on its results of operations and financial position. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. The new guidance modifies ASC 740 to simplify several aspects of accounting for income taxes, including eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation. ASU 2019-12 will be effective for the Company for its fiscal year beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022, and is required to be adopted prospectively, with the exception of certain specific amendments. The Company is currently assessing the timing of adoption and the impact that the adoption of ASU 2019 ‑

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Estimated Useful Life of Asset	Depreciation is recognized using the straight-line method based on an estimated useful life of the asset, which is as follows: Computer equipment 3 years Laboratory equipment and office furniture 3 years Leasehold improvement Shorter of life of asset or lease term
Computation of Net Loss Per Share	Net loss per share were computed as follows (in thousands, except share and per share amounts): Year Ended December 31, 2020 2019 2018 Numerator: Net loss $ (102,487 ) $ (42,795 ) $ (493 ) Denominator: Weighted average number of shares used in calculating net loss per share—basic and diluted 68,475,378 50,297,524 6,383,751 Net loss per share—basic and diluted $ (1.50 ) $ (0.85 ) $ (0.08 )
Potentially Dilutive Securities Not Included in Diluted Per Share Calculations	Potentially dilutive securities that were not included in the diluted per share calculations because they would be anti-dilutive were as follows: Year Ended December 31, 2020 2019 2018 Convertible preferred stock — — 47,267,466 Options to purchase common stock 10,017,918 10,824,780 9,806,689 Shares committed under ESPP 291,992 396,682 - Warrants to purchase convertible preferred stock — — 19,637 Total 10,309,910 11,221,462 57,093,792

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Cash and Cash Equivalents and Marketable Securities Classified as Available-for-sale Securities	Cash and cash equivalents and marketable securities, all of which are classified as available-for-sale securities, consisted of the following (in thousands): Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value As of December 31, 2020 Money market funds $ 137,658 $ — $ — $ 137,658 U.S. government agencies securities 98,647 9 (3 ) 98,653 Commercial paper 41,945 — — 41,945 Corporate and agency bonds 7,543 — (2 ) 7,541 Totals $ 285,793 $ 9 $ (5 ) $ 285,797 Classified as: Cash and cash equivalents $ 137,658 Short-term marketable securities (amortized cost of $148,135) 148,139 Total $ 285,797 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value As of December 31, 2019 Money market funds $ 244,973 $ — $ — $ 244,973 Corporate and agency bonds 66,063 28 (14 ) 66,077 Commercial paper 24,840 — — 24,840 U.S. government agencies securities 7,985 11 — 7,996 Totals $ 343,861 $ 39 $ (14 ) $ 343,886 Classified as: Cash and cash equivalents $ 244,973 Short-term marketable securities (amortized cost of $98,888) 98,913 Total $ 343,886
Summary of Available-for-sale Securities Measured at Fair Value on Recurring Basis	The following table summarizes, by major security type, our available-for-sale securities that were measured at fair value on a recurring basis and were categorized using the fair value hierarchy (in thousands): Fair Value Measurements As of December 31, 2020 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 137,658 $ — $ — $ 137,658 U.S. government agencies securities — 98,653 — 98,653 Commercial paper — 41,945 — 41,945 Corporate and agency bonds — 7,541 — 7,541 Totals $ 137,658 $ 148,139 $ — $ 285,797 Fair Value Measurements As of December 31, 2019 Level 1 Level 2 Level 3 Total Assets: Money market funds $ 244,973 $ — $ — $ 244,973 Corporate and agency bonds — 66,077 — 66,077 Commercial paper — 24,840 — 24,840 U.S. government agencies securities — 7,996 — 7,996 Totals $ 244,973 $ 98,913 $ — $ 343,886

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalent and Restricted Cash	A reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets to the amount reported within the consolidated statements of cash flows is as follows (in thousands): December 31, 2020 2019 Cash and cash equivalents $ 147,017 $ 245,598 Restricted cash 1,499 1,874 Total cash, cash equivalents and restricted cash $ 148,516 $ 247,472
Property and Equipment	Property and equipment consisted of the following (in thousands): December 31, 2020 2019 Leasehold improvements $ 25,880 $ 25,880 Laboratory equipment and office furniture 23,638 21,652 Computer equipment 1,271 1,201 Construction-in-progress 48 498 Total property and equipment, gross 50,837 49,231 Less: accumulated depreciation and amortization (36,311 ) (29,756 ) Total property and equipment, net $ 14,526 $ 19,475
Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): December 31, 2020 2019 Clinical trials and research and development costs $ 9,316 $ 11,051 Manufacturing costs 8,297 2,593 Personnel-related costs 8,921 6,446 Accrued expenses 3,411 2,901 Total accrued liabilities $ 29,945 $ 22,991

Research Collaboration and Li_2

Research Collaboration and License Agreements (Tables)	12 Months Ended
	Dec. 31, 2020
Collaboration And License Agreement Disclosure [Abstract]
Schedule of Milestone Payments by Indications	A breakout of the milestone payments in connection with the potential achievement of certain clinical development events is as follows (in thousands): First Indication Second Indication Third Indication Upon administration of an applicable product to the first patient in the first Phase 3 clinical trial for such product for the given indication $ 35,000 $ 25,250 $ 17,500 A breakout of the milestone payments in connection with the potential achievement of various regulatory events for each of the three indications, for each of the three geographic areas, is as follows (in thousands): First Indication Second Indication Third Indication Total United States $ 75,000 $ 56,250 $ 37,500 $ 168,750 European Union 60,000 45,000 30,000 135,000 Japan 30,000 22,500 15,000 67,500 $ 165,000 $ 123,750 $ 82,500 $ 371,250
Schedule of Recognized Revenue from Collaboration and License Agreements	The Company recognized revenue from its collaboration and license agreements as follows (in thousands): Year Ended December 31, 2020 2019 2018 Related party revenue $ 87,368 $ 103,544 $ 108,665
Schedule of Changes in Contract Liabilities	Changes in contract liabilities were as follows (in thousands): Amounts Balance at December 31, 2018 $ 22,967 Adoption of ASC 606 6,156 Balance at January 1, 2019 29,123 Revenue recognized included in the contract liability balance at the beginning of the period (24,251 ) Balance at December 31, 2019 4,872 Revenue recognized through March 16, 2020 (4,872 ) Balance at December 31, 2020 $ -

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Future Minimum Commitments under Unassigned Lease Obligations	Future minimum payments under the unassigned lease obligations described above are as follows as of December 31, 2020 (in thousands): Year Ended December 31, 2021 $ 5,141 2022 5,294 2023 5,455 Total $ 15,890

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2020
Schedule of Shares of Common Stock Reserved for Issuance	The Company had reserved the following shares of common stock for issuance: December 31, 2020 2019 Reserve balance for Sales Agreement 14,190,300 - Common stock options outstanding 10,017,918 10,824,780 Common stock options available for grant 6,186,497 5,316,066 ESPP shares available for purchase 700,074 897,255 401(k) matching plan 21,930 28,274 Total 31,116,719 17,066,375
Summary of Outstanding Stock Options	A summary of the outstanding stock options is as follows: Outstanding Options Options Available for Grant Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Life (in Years) Aggregate Intrinsic Value (in Thousands) Balances at December 31, 2019 5,316,066 10,824,780 $ 7.52 6.29 $ 118,770 Additional shares reserved 2,678,411 Options granted (2,576,501 ) 2,576,501 17.62 Options exercised — (2,614,842 ) 4.53 Options cancelled 768,521 (768,521 ) 12.43 Balances at December 31, 2020 6,186,497 10,017,918 $ 10.52 6.45 $ 198,097 Vested and expected to vest at December 31, 2020 9,872,681 $ 10.44 6.41 $ 196,065 Outstanding and exercisable at December 31, 2020 10,017,918 $ 10.52 6.45 $ 198,097
Summary of Stock Based Compensation Expense	Stock-based compensation expense related to Year Ended December 31, 2020 2019 2018 Research and development $ 8,145 $ 7,145 $ 5,232 General and administrative 7,312 5,584 4,524 Total stock-based compensation expense $ 15,457 $ 12,729 $ 9,756
Summary of Fair Value of Stock Option to Employees and Directors were Estimated at Date of Grant Using Black-Scholes Option-pricing Model	The fair value of stock option awards granted to employees and directors were estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted average valuation assumptions: Year Ended December 31, 2020 2019 2018 Volatility 68 % 65 % 65 % Expected term (years) 6.23 6.18 5.98 Risk-free interest rate 1.04 % 2.25 % 2.59 % Expected dividend yield — — —
2019 Employee Stock Purchase Plan
Summary of Fair Value of Stock Option to Employees and Directors were Estimated at Date of Grant Using Black-Scholes Option-pricing Model	The fair value of the rights granted to employees under the ESPP was estimated at the date of offer using a Black-Scholes option-pricing model with the following weighted average valuation assumptions: Year Ended December 31, 2020 2019 2018 Volatility 74 % 59 % — Expected term (years) 1.17 1.23 — Risk-free interest rate 0.15 % 1.97 % — Expected dividend yield — — —
Non-employees
Summary of Fair Value of Stock Option Granted to Non-Employees was Estimated at Date of Grant Using Black-Scholes Option-pricing Model	The fair value of stock option awards granted to non-employees was estimated at the date of grant using a Black-Scholes option-pricing model with the following weighted average valuation assumptions: Year Ended December 31, 2020 2019 2018 Volatility 70 % 66 % — Expected term (years) 6.02 6.00 — Risk-free interest rate 0.41 % 2.26 % — Expected dividend yield — — —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of Components of Losses Before Income Taxes	The components of the Company’s losses before income taxes were as follows (in thousands): Year Ended December 31, 2020 2019 2018 Domestic $ (102,209 ) $ (34,634 ) $ 5,502 Foreign (278 ) (8,161 ) (5,995 ) Total $ (102,487 ) $ (42,795 ) $ (493 )
Schedule of Reconciliation of Statutory U.S. Federal Rate to Effective Tax Rate	A reconciliation of the statutory U.S. federal rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2020 2019 2018 U.S. federal tax at statutory rate 21.0 % 21.0 % 21.0 % Foreign tax rate differential 0.0 1.7 109.5 State, net of federal benefit (0.1 ) 0.0 (4.5 ) Stock-based compensation 3.8 0.2 (93.1 ) Change in valuation allowance (25.0 ) (23.2 ) 401.6 Other 0.3 0.2 (434.7 ) Total 0.0 % 0.0 % (0.2 ) %
Schedule of Components of Net Deferred Tax Assets	The components of the net deferred tax assets are as follows (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 60,879 $ 37,679 Stock-based compensation 4,580 3,478 Research and development credit 2,918 2,918 Contract liabilities — 1,026 Other temporary differences 2,079 1,217 Total gross deferred tax assets 70,456 46,318 Deferred tax liabilities: Depreciation and amortization (389 ) (570 ) Non-qualified stock options with 83(b) election (15 ) (15 ) Total gross deferred tax liabilities (404 ) (585 ) Net deferred tax assets before valuation allowance 70,052 45,733 Deferred tax asset valuation allowance (70,052 ) (45,733 ) Net deferred tax assets $ — $ —
Schedule of Reconciliation of Unrecognized Tax Benefits	A reconciliation of the Company’s unrecognized tax benefits is as follows (in thousands): December 31, 2020 2019 2018 Balance at beginning of year $ 3,819 $ 3,819 $ 1,528 Additions based on tax positions related to prior year 314 — 2,291 Additions based on tax positions related to current year 6,213 — — Balance at end of year $ 10,346 $ 3,819 $ 3,819

Organization and Description _2

Organization and Description of Business - Additional Information (Details) $ / shares in Units, $ in Thousands	Apr. 08, 2019USD ($)$ / sharesshares	Mar. 22, 2019	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)
Subsidiary Sale Of Stock [Line Items]
Place of incorporation			DE
Date of incorporation			Dec. 31, 2007
Common stock reverse stock split ratio		2
Underwriting discounts and commissions as well as offering expenses			$ 613		$ 2,200
Reclassification to common stock and additional paid-in capital				$ 295,072
Proceeds from issuance of stock				$ 65,947
Merck Sharp & Dohme Corp
Subsidiary Sale Of Stock [Line Items]
Percentage of outstanding shares of common stock owned by related party	19.90%
IPO
Subsidiary Sale Of Stock [Line Items]
Common stock issued upon conversion of convertible preferred stock | shares	47,283,839
Common Stock
Subsidiary Sale Of Stock [Line Items]
Number of shares issued in transaction | shares	7,521,394			7,521,000
Common stock issued upon conversion of convertible preferred stock | shares				47,283,000
Reclassification to common stock and additional paid-in capital	$ 295,100			$ 47
Proceeds from issuance of stock	$ 65,900
Common Stock | Over-Allotment Option
Subsidiary Sale Of Stock [Line Items]
Number of shares issued in transaction | shares	854,727
Share price | $ / shares	$ 16
Common Stock | IPO
Subsidiary Sale Of Stock [Line Items]
Share price | $ / shares	$ 16
Proceeds from issuance of common stock, net of underwriters discount and commissions	$ 107,800
Underwriting discounts and commissions as well as offering expenses	$ 4,100				$ 2,200
Common Stock | Private Placement
Subsidiary Sale Of Stock [Line Items]
Number of shares issued in transaction | shares	4,121,683
Share price | $ / shares	$ 16

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	Jan. 05, 2021USD ($)	Jan. 31, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2020USD ($)Segment$ / shares	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Jan. 01, 2019USD ($)	Dec. 31, 2017USD ($)
Summary Of Significant Accounting Policies [Line Items]
Net losses				$ 102,487,000	$ 42,795,000	$ 493,000
Accumulated deficit			$ 298,631,000	298,631,000	196,144,000
Cash, cash equivalents and short-term marketable securities			295,200,000	295,200,000
Impairment related to other-than-temporary				0
Stockholders equity			$ (280,043,000)	$ (280,043,000)	$ (330,719,000)	108,195,000		$ 120,978,000
Number of operating segment | Segment				1
ASU 2018-13
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]			true	true
Change in accounting principle, accounting standards update, adoption date			Jan. 1, 2020	Jan. 1, 2020
Change in accounting principle, accounting standards update, immaterial effect [true false]			true	true
Cumulative Effect Period of Adoption Adjustment
Summary Of Significant Accounting Policies [Line Items]
Stockholders equity						$ 6,156,000	$ 6,200,000
Revenue | Customer Concentration Risk | Merck
Summary Of Significant Accounting Policies [Line Items]
Percentage of revenue				100.00%	100.00%	100.00%
Underwritten Public Offering | Subsequent Event
Summary Of Significant Accounting Policies [Line Items]
Common stock purchased by related party | shares		5,324,074
Public offering price of common stock | $ / shares		$ 27
Net proceeds from sale of common stock	$ 134,700,000	$ 134,700,000
Common Stock
Summary Of Significant Accounting Policies [Line Items]
Stockholders equity			$ (71,000)	$ (71,000)	$ (67,000)	$ (7,000)		(6,000)
Accumulated Deficit
Summary Of Significant Accounting Policies [Line Items]
Net losses				102,487,000	42,795,000	493,000
Stockholders equity			298,631,000	298,631,000	$ 196,144,000	147,193,000		$ 146,700,000
Accumulated Deficit | Cumulative Effect Period of Adoption Adjustment
Summary Of Significant Accounting Policies [Line Items]
Stockholders equity						$ 6,156,000	$ 6,200,000
Open Market Sale Agreement | Common Stock
Summary Of Significant Accounting Policies [Line Items]
Common stock available for sale			$ 127,400,000	$ 127,400,000
Open Market Sale Agreement | Jefferies LLC | Common Stock
Summary Of Significant Accounting Policies [Line Items]
Common stock purchased by related party | shares			809,700
Public offering price of common stock | $ / shares			$ 27.94	$ 27.94
Net proceeds from sale of common stock			$ 21,900,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Estimated Useful Life of Asset (Details)	12 Months Ended
	Dec. 31, 2020
Computer Equipment
Property Plant And Equipment [Line Items]
Estimated useful life of asset	3 years
Laboratory Equipment and Office Furniture
Property Plant And Equipment [Line Items]
Estimated useful life of asset	3 years
Leasehold Improvement
Property Plant And Equipment [Line Items]
Leasehold improvement	Shorter of life of asset or lease term

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Computation of Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss	$ (102,487)	$ (42,795)	$ (493)
Denominator:
Weighted average shares used to compute net loss per share, basic and diluted	68,475,378	50,297,524	6,383,751
Net loss per share—basic and diluted	$ (1.50)	$ (0.85)	$ (0.08)

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Potentially Dilutive Securities Not Included in Diluted Per Share Calculations (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in calculations of diluted per share	10,309,910	11,221,462	57,093,792
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in calculations of diluted per share			47,267,466
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in calculations of diluted per share	10,017,918	10,824,780	9,806,689
Warrants to Purchase Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in calculations of diluted per share			19,637
Shares Committed Under ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities not included in calculations of diluted per share	291,992	396,682

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Cash and Cash Equivalents and Marketable Securities Classified as Available-for-sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 285,793	$ 343,861
Gross Unrealized Gain	9	39
Gross Unrealized Loss	(5)	(14)
Fair Value	285,797	343,886
Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	137,658	244,973
Fair Value	137,658	244,973
Corporate and Agency Bonds
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	7,543	66,063
Gross Unrealized Gain		28
Gross Unrealized Loss	(2)	(14)
Fair Value	7,541	66,077
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	41,945	24,840
Fair Value	41,945	24,840
U.S. Government Agencies Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	98,647	7,985
Gross Unrealized Gain	9	11
Gross Unrealized Loss	(3)
Fair Value	98,653	7,996
Cash and Cash Equivalents
Schedule Of Available For Sale Securities [Line Items]
Fair Value	137,658	244,973
Short-term Marketable Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	148,135	98,888
Fair Value	$ 148,139	$ 98,913

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Cash and Cash Equivalents and Marketable Securities Classified as Available-for-sale Securities (Parenthetical) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 285,793	$ 343,861
Short-term Marketable Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 148,135	$ 98,888

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	Dec. 31, 2020USD ($)Security	Dec. 31, 2019USD ($)Security
Fair Value Disclosures [Abstract]
Cash on deposit with banks	$ 9,400,000	$ 600,000
Number of marketable securities in unrealized loss positions less than 12 months | Security	1	4
Fair value, assets, level 1 to level 2 transfers, amount	$ 0	$ 0
Fair value, assets, level 2 to level 1 transfers, amount	0	0
Fair value, liabilities, level 1 to level 2 transfers, amount	0	0
Fair value, liabilities, level 2 to level 1 transfers, amount	$ 0	$ 0

Fair Value Measurements - Sum_3

Fair Value Measurements - Summary of Available-for-sale Securities Measured at Fair Value on Recurring Basis (Details) - Fair Value Measurements, Recurring - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets:
Assets fair value	$ 285,797	$ 343,886
Money Market Funds
Assets:
Assets fair value	137,658	244,973
Corporate and Agency Bonds
Assets:
Assets fair value	7,541	66,077
Commercial Paper
Assets:
Assets fair value	41,945	24,840
U.S. Government Agencies Securities
Assets:
Assets fair value	98,653	7,996
Level 1
Assets:
Assets fair value	137,658	244,973
Level 1 | Money Market Funds
Assets:
Assets fair value	137,658	244,973
Level 2
Assets:
Assets fair value	148,139	98,913
Level 2 | Corporate and Agency Bonds
Assets:
Assets fair value	7,541	66,077
Level 2 | Commercial Paper
Assets:
Assets fair value	41,945	24,840
Level 2 | U.S. Government Agencies Securities
Assets:
Assets fair value	$ 98,653	$ 7,996

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Reconciliation of Cash, Cash Equivalent and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Cash and cash equivalents	$ 147,017	$ 245,598
Restricted cash	1,499	1,874
Total cash, cash equivalents and restricted cash	$ 148,516	$ 247,472	$ 59,172	$ 27,842

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 50,837	$ 49,231
Less: accumulated depreciation and amortization	(36,311)	(29,756)
Total property and equipment, net	14,526	19,475
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,271	1,201
Laboratory Equipment and Office Furniture
Property Plant And Equipment [Line Items]
Property and equipment, gross	23,638	21,652
Leasehold Improvement
Property Plant And Equipment [Line Items]
Property and equipment, gross	25,880	25,880
Construction In Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 48	$ 498

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Depreciation expense	$ 6,555	$ 7,605	$ 7,223

Balance Sheet Components - Sc_3

Balance Sheet Components - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Clinical trials and research and development costs	$ 9,316	$ 11,051
Manufacturing costs	8,297	2,593
Personnel-related costs	8,921	6,446
Accrued expenses	3,411	2,901
Total accrued liabilities	$ 29,945	$ 22,991

Research Collaboration and Li_3

Research Collaboration and License Agreements - Additional Information (Details)	Apr. 08, 2019	Nov. 30, 2018USD ($)	Apr. 30, 2015USD ($)	Dec. 31, 2020USD ($)Option$ / sharesshares	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2020USD ($)Option$ / shares	Mar. 31, 2020USD ($)	Nov. 29, 2018USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue					$ 4,872,000
Collaboration and license revenue				$ 87,368,000	103,544,000	$ 108,665,000
Contract assets				6,100,000			$ 6,100,000
Deferred revenue recognized				$ 4,872,000	24,251,000
Merck Sharp & Dohme Corp
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of outstanding shares of common stock owned by related party	19.90%
Collaboration Agreement | Merck Sharp & Dohme Corp
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash licensing fee			$ 94,000,000
Fair values of assets and services exchanged allocated to equity component			106,000,000
Fair values of assets and services exchanged allocated to revenue component			94,000,000
Term of agreement				5 years
Research and development services additional option extend term				2 years
Amount of fund received for research activities				$ 20,000,000
Amount of additional fund received for research activities				20,000,000	20,000,000
Research collaboration and license agreements extension fee				$ 20,000,000
Research and development collaboration agreement additional term description				As part of the two-year extension through March 16, 2022, Merck agreed to continue to fund the Company’s research and development efforts up to $75.0 million each year consistent with the initial five-year term and, in lieu of a $20.0 million extension fee that would have otherwise been payable to the Company, Merck agreed to make additional payments totaling up to $20.0 million in support of the Company’s research and development program activities during 2021 and in the first quarter of 2022.
Decision on extension for annual research support deadline date				Jun. 30, 2021
License fee				$ 20,000,000			$ 20,000,000		$ 20,000,000
Share of global development costs				25.00%
Performance of R&D services period				5 years
Number of options to extend performance of research program | Option				2			2
Received amount from options		$ 20,000,000
Upfront Fee				$ 94,000,000
Collaborative agreement milestone or other forms of consideration				0
Deferred revenue					4,900,000			$ 4,900,000
Collaboration and license revenue				87,400,000	103,500,000	108,700,000	$ 388,100,000
Revenue transaction price				170,000,000
Contract assets				6,100,000			6,100,000
Deferred revenue recognized					6,200,000
Upfront license fee					$ 24,000,000
Amortized of upfront payments						18,800,000
Remaining performance obligation				61,800,000			$ 61,800,000
Collaboration Agreement | Merck Sharp & Dohme Corp | MK-3655
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue				4,900,000		$ 20,000,000
Collaboration Agreement | Merck Sharp & Dohme Corp | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development and regulatory milestone payments eligible to receive				449,000,000
Commercial milestone payments received				125,000,000
Collaborative arrangement funding, amount				$ 75,000,000
Collaboration Agreement | Merck Sharp & Dohme Corp | Series E Convertible Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from issuance of preferred stock			$ 106,000,000
Small Molecule Compounds | Merck Sharp & Dohme Corp
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional term				3 years
Side Letter Agreement | Merck Sharp & Dohme Corp
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Public offering price of common stock | $ / shares				$ 16			$ 16
Percentage of outstanding shares of common stock owned by related party				19.90%
Side Letter Agreement | Merck Sharp & Dohme Corp | Private Placement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Common stock purchased by related party | shares				4,121,683

Research Collaboration and Li_4

Research Collaboration and License Agreements - Schedule of Milestone Payments by Indications (Details) - Collaboration Agreement $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	$ 371,250
First Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	165,000
Second Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	123,750
Third Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	82,500
United States
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	168,750
United States | First Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	75,000
United States | Second Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	56,250
United States | Third Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	37,500
European Union
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	135,000
European Union | First Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	60,000
European Union | Second Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	45,000
European Union | Third Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	30,000
Japan
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	67,500
Japan | First Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	30,000
Japan | Second Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	22,500
Japan | Third Indication
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments in connection with potential achievement of certain regulatory events	15,000
First Indication | Clinical Trial to First Patient in First Phase 3
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upon administration of an applicable product to the first patient in the first Phase 3 clinical trial for such product for the given indication	35,000
Second Indication | Clinical Trial to First Patient in First Phase 3
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upon administration of an applicable product to the first patient in the first Phase 3 clinical trial for such product for the given indication	25,250
Third Indication | Clinical Trial to First Patient in First Phase 3
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upon administration of an applicable product to the first patient in the first Phase 3 clinical trial for such product for the given indication	$ 17,500

Research Collaboration and Li_5

Research Collaboration and License Agreements - Schedule of Recognized Revenue from Collaboration and License Agreements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Collaboration Agreement | Merck Sharp & Dohme Corp
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Related party revenue	$ 87,368	$ 103,544	$ 108,665

Research Collaboration and Li_6

Research Collaboration and License Agreements - Schedule of Changes in Contract Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Beginning Balance	$ 4,872
Revenue recognized	$ (4,872)	$ (24,251)
Ending Balance		4,872
Amount Under ASC 605
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Beginning Balance		22,967
Cumulative Effect Period of Adoption Adjustment | ASC 606
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Beginning Balance		6,156
Cumulative Effect, Period of Adoption, Adjusted Balance
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Beginning Balance		$ 29,123

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	1 Months Ended		12 Months Ended
	Dec. 31, 2015USD ($)ft²	Sep. 30, 2009USD ($)ft²	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Commitments And Contingencies Disclosure [Line Items]
Total Leasehold improvements			$ 14,526,000	$ 19,475,000
Corporate Office Space and Laboratory Facility
Commitments And Contingencies Disclosure [Line Items]
Area of leased property | ft²	122,000	50,000
Operating lease agreement, expiration period	2023-12	2020-11
Tenant improvement allowances	$ 15,200,000
Operating lease agreement, amended period		2014-06
Rent expense			2,200,000	$ 2,200,000	$ 2,200,000
Corporate Office Space and Laboratory Facility | Landlord and Merck
Commitments And Contingencies Disclosure [Line Items]
Operating lease payment obligations		$ 0
Corporate Office Space and Laboratory Facility | Letter of Credit
Commitments And Contingencies Disclosure [Line Items]
Letter of credit as a security deposit	2,300,000
Reduction in letter of credit on each of third anniversary and fourth anniversary	400,000
Corporate Office Space and Laboratory Facility | Letter of Credit | Cash and Cash Equivalents
Commitments And Contingencies Disclosure [Line Items]
Reduction in letter of credit			$ 400,000
Corporate Office Space and Laboratory Facility | Leasehold Improvement
Commitments And Contingencies Disclosure [Line Items]
Total Leasehold improvements	$ 22,300,000
Operating lease term	7 years

Commitments and Contingencies_2

Commitments and Contingencies - Future Minimum Commitments under Unassigned Lease Obligations (Details) $ in Thousands	Dec. 31, 2020USD ($)
Commitments And Contingencies Disclosure [Abstract]
2021	$ 5,141
2022	5,294
2023	5,455
Total	$ 15,890

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details)	1 Months Ended			12 Months Ended
	Dec. 31, 2020USD ($)$ / sharesshares	Jun. 30, 2020USD ($)	Mar. 31, 2019Periodshares	Dec. 31, 2020USD ($)$ / sharesshares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares
Class Of Stock [Line Items]
Preferred stock, shares authorized	10,000,000			10,000,000	10,000,000
Preferred stock, shares issued	0			0	0
Preferred stock, shares outstanding	0			0	0
Common stock, shares outstanding	70,585,364			70,585,364	66,960,279
Stock repurchase plan, authorized shares	6,508			6,508	74,454
Number of shares of common stock reserved for issuance	31,116,719			31,116,719	17,066,375
Common stock issued	70,585,364			70,585,364	66,960,279
Weighted-average grant date fair value of stock options ,Granted | $ / shares				$ 10.86	$ 8	$ 5.71
Intrinsic value of stock options exercised | $				$ 40,900,000	$ 10,200,000	$ 1,900,000
Tax benefits realized | $				$ 0	0	0
Options granted				2,576,501
Employees and Directors
Class Of Stock [Line Items]
Stock-based compensation expense | $				$ 15,457,000	12,729,000	9,756,000
Total compensation cost not yet recognized | $	$ 29,600,000			$ 29,600,000
Unrecognized compensation cost expected to be recognized over a weighted-average period				2 years 9 months
Non-employees
Class Of Stock [Line Items]
Stock-based compensation expense | $				$ 194,000	$ 133,000	$ 103,000
Options granted				67,500	22,500	0
Stock options to purchase shares, remain unvested	70,472			70,472	21,564
2018 Plan
Class Of Stock [Line Items]
Common stock, shares outstanding	6,508			6,508	74,454
Common stock authorized for issuance	17,874,624			17,874,624
Percentage of number of shares reserved and available to issue automatically increase outstanding on preceding calendar year				4.00%
Right to repurchase shares lapses over period				4 years
Early exercise stock option liabilities | $	$ 100,000			$ 100,000	$ 600,000
2019 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Number of shares of common stock reserved for issuance			1,000,000
Number of shares reserved and available for issuance, description				the number of shares reserved and available for issuance will automatically increase on January 1 of each calendar year, beginning January 1, 2020, by the lesser of (1) 1.0% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, (2) 1,000,000 shares or (3) a number determined by the Company’s board of directors that is less than (1) and (2).
Maximum percentage of payroll deductions of employee's compensation			15.00%
Maximum duration for purchase under employee stock purchase plan			24 months
Number of purchase periods | Period			4
Duration of each purchase period			6 months
Percentage of purchase of common stock fair market value			85.00%
Stock-based compensation expense | $				$ 1,200,000	$ 1,000,000
Common stock issued	299,926			299,926
Maximum | 2018 Plan
Class Of Stock [Line Items]
Stock options, vesting period				10 years
Share repurchase price per Share | $ / shares	$ 8.14			$ 8.14	$ 8.14
Maximum | 2018 Plan | IPO | 10% or Greater Stockholder
Class Of Stock [Line Items]
Stock option expiration period				10 years
Minimum | 2018 Plan
Class Of Stock [Line Items]
Stock options, vesting period				4 years
Share repurchase price per Share | $ / shares	$ 7.70			$ 7.70	$ 7.64
Minimum | 2018 Plan | IPO
Class Of Stock [Line Items]
Percentage of exercise price to fair market value common stock on grant date				100.00%
Minimum | 2018 Plan | IPO | 10% or Greater Stockholder
Class Of Stock [Line Items]
Percentage of exercise price to fair market value common stock on grant date				110.00%
Stock option expiration period				5 years
Jefferies LLC | Open Market Sale Agreement
Class Of Stock [Line Items]
Number of shares issued in transaction	809,700
Share price | $ / shares	$ 27.94			$ 27.94
Proceeds from issuance of common stock, net of underwriters discount and commissions | $	$ 21,900,000
Sales commissions | $	700,000
Deferred offering costs | $	600,000			$ 600,000
Common stock, available for issuance value | $	$ 127,400,000			$ 127,400,000
Jefferies LLC | Open Market Sale Agreement | Maximum
Class Of Stock [Line Items]
Sale of common stock, Aggregate price | $		$ 150,000,000

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Shares of Common Stock Reserved for Issuance (Details) - shares	Dec. 31, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Total	31,116,719	17,066,375
Common Stock Options Outstanding
Class Of Stock [Line Items]
Total	10,017,918	10,824,780
Common Stock Options Available for Grant
Class Of Stock [Line Items]
Total	6,186,497	5,316,066
Reserve balance for Sales Agreement
Class Of Stock [Line Items]
Total	14,190,300
401(k) Matching Plan
Class Of Stock [Line Items]
Total	21,930	28,274
Shares Committed Under ESPP
Class Of Stock [Line Items]
Total	700,074	897,255

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Outstanding Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Outstanding Options, Options Available for Grant, Beginning balance	5,316,066
Outstanding Options, Options Available for Grant, Additional Shares	2,678,411
Outstanding Options, Options Available for Grant, Granted	(2,576,501)
Outstanding Options, Options Available for Grant, Cancelled	768,521
Outstanding Options, Options Available for Grant, Ending balance	6,186,497	5,316,066
Outstanding Options, Number of Options, Beginning balance	10,824,780
Outstanding Options, Number of Options, Granted	2,576,501
Outstanding Options, Number of Options, Exercised	(2,614,842)
Outstanding Options, Number of Options, Cancelled	(768,521)
Outstanding Options, Number of Options, Ending balance	10,017,918	10,824,780
Outstanding Options, Number of Options, Options vested and expected to vest	9,872,681
Outstanding Options, Number of Options, Options exercisable	10,017,918
Outstanding Options, Weighted-Average Exercise Price, Beginning balance	$ 7.52
Outstanding Options, Weighted-Average Exercise Price, Granted	17.62
Outstanding Options, Weighted-Average Exercise Price, Exercised	4.53
Outstanding Options, Weighted-Average Exercise Price, Cancelled	12.43
Outstanding Options, Weighted-Average Exercise Price, Ending balance	10.52	$ 7.52
Outstanding Options, Weighted-Average Exercise Price, Options vested and expected to vest	10.44
Outstanding Options, Weighted-Average Exercise Price, Options exercisable	$ 10.52
Weighted Average Remaining Contractual Life (in Years)	6 years 5 months 12 days		6 years 3 months 14 days
Weighted Average Remaining Contractual Life (in Years), Vested and expected to vest	6 years 4 months 28 days
Weighted Average Remaining Contractual Life (in Years),Outstanding and Exercisable	6 years 5 months 12 days
Outstanding Options, Aggregate Intrinsic Value, Balance	$ 198,097	$ 118,770
Outstanding Options, Aggregate Intrinsic Value, Options vested and expected to vest-December 31, 2020	196,065
Options Outstanding, Aggregate Intrinsic Value, Options exercisable-December 31, 2020	$ 198,097

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Stock Based Compensation Expense (Details) - Employees and Directors - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 15,457	$ 12,729	$ 9,756
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	8,145	7,145	5,232
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 7,312	$ 5,584	$ 4,524

Stockholders' Equity - Summar_3

Stockholders' Equity - Summary of Fair Value of Stock Option Granted to Employees and Directors were Estimated at Date of Grant Using Black-Scholes Option-pricing Model (Details) - Employees and Directors	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility	68.00%	65.00%	65.00%
Expected term (years)	6 years 2 months 23 days	6 years 2 months 4 days	5 years 11 months 23 days
Risk-free interest rate	1.04%	2.25%	2.59%

Stockholders' Equity - Summar_4

Stockholders' Equity - Summary of Fair Value of Stock Option Granted to Non-Employees was Estimated at Date of Grant Using Black-Scholes Option-pricing Model (Details) - Non-employees	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility	70.00%	66.00%
Expected term (years)	6 years 7 days	6 years
Risk-free interest rate	0.41%	2.26%

Stockholders' Equity - Summar_5

Stockholders' Equity - Summary of Fair Value of the Rights Granted to Employees Under the 2019 ESPP was Estimated at the Date of Offer Using Black-Scholes Option-pricing Model (Details) - 2019 Employee Stock Purchase Plan	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility	74.00%	59.00%
Expected term (years)	1 year 2 months 1 day	1 year 2 months 23 days
Risk-free interest rate	0.15%	1.97%

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Issuance of common stock to participants in 401(k) Plan	$ 119,000	$ 98,000	$ 91,000
401(k)
Defined Benefit Plan Disclosure [Line Items]
Percentage of contribution matched by employer in common stock	50.00%
Maximum annual contributions of common stock per employee per year	$ 750
Common stock reserved for future issuance	21,930	28,274
Issuance of common stock to participants in 401(k) Plan, shares	6,344	8,477
Issuance of common stock to participants in 401(k) Plan	$ 119,000	$ 98,000

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Losses Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Domestic	$ (102,209)	$ (34,634)	$ 5,502
Foreign	(278)	(8,161)	(5,995)
Total	$ (102,487)	$ (42,795)	$ (493)

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Statutory U.S. Federal Rate to Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
U.S. federal tax at statutory rate	21.00%	21.00%	21.00%
Foreign tax rate differential	0.00%	1.70%	109.50%
State, net of federal benefit	(0.10%)	0.00%	(4.50%)
Stock-based compensation	3.80%	0.20%	(93.10%)
Change in valuation allowance	(25.00%)	(23.20%)	401.60%
Other	0.30%	0.20%	(434.70%)
Total	0.00%	0.00%	(0.20%)

Income Taxes - Schedule of Co_2

Income Taxes - Schedule of Components of Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 60,879	$ 37,679
Stock-based compensation	4,580	3,478
Research and development credit	2,918	2,918
Contract liabilities		1,026
Other temporary differences	2,079	1,217
Total gross deferred tax assets	70,456	46,318
Deferred tax liabilities:
Depreciation and amortization	(389)	(570)
Non-qualified stock options with 83(b) election	(15)	(15)
Total gross deferred tax liabilities	(404)	(585)
Net deferred tax assets before valuation allowance	70,052	45,733
Deferred tax asset valuation allowance	$ (70,052)	$ (45,733)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Valuation allowance, increase amount	$ 24,300,000	$ 9,500,000
Research and development tax credits	2,918,000	2,918,000
Unrecognized tax benefits, accrued interest and penalties	0	0
Federal [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 226,800,000			$ 161,400,000
Net operating loss carryforwards expiration period			20 years
Net operating loss carryforwards expiration year			2032
Operating loss carryforwards, limitations on use	Subsequent to the enactment of the 2017 Tax Act, the utilization of the federal net operating loss carryforwards generated in fiscal year 2018 and onwards is limited to 80% of the federal taxable income.
Percentage of net operating loss carryforwards utilization limit of taxable income subsequent to enactment of 2017 tax act	80.00%
Research and development tax credits	$ 3,100,000	3,100,000
Federal [Member] | Earliest Tax Year [Member]
Income Tax Disclosure [Line Items]
Research and development credits expiration year	2028
Federal [Member] | Latest Tax Year [Member]
Income Tax Disclosure [Line Items]
Research and development credits expiration year	2035
State [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 145,800,000
Net operating loss carryforwards expiration year	2028
Research and development tax credits	$ 4,000,000	4,000,000
Foreign [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 35,800,000	$ 29,700,000

Income Taxes - Schedule of Re_2

Income Taxes - Schedule of Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 3,819	$ 3,819	$ 1,528
Additions based on tax positions related to prior year	314		2,291
Additions based on tax positions related to current year	6,213
Balance at end of year	$ 10,346	$ 3,819	$ 3,819

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 05, 2021	Jan. 31, 2021	Dec. 31, 2020
Collaboration Agreement | Merck Sharp & Dohme Corp
Subsequent Event [Line Items]
Research and development services additional option extend term			2 years
Decision on extension for annual research support deadline date			Jun. 30, 2021
Subsequent Event | Underwritten Public Offering
Subsequent Event [Line Items]
Number of shares issued in transaction	4,629,630
Share price	$ 27
Additional common stock, option to purchase	694,444
Net proceeds from offering	$ 134.7	$ 134.7