Arcus Biosciences (RCUS) 10-K 25 Feb 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 12, 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	RCUS
Entity Registrant Name	Arcus Biosciences, Inc.
Entity Central Index Key	0001724521
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity File Number	001-38419
Entity Tax Identification Number	47-3898435
Entity Address, Address Line One	3928 Point Eden Way
Entity Address, City or Town	Hayward
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94545
City Area Code	510
Local Phone Number	694-6200
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, Par Value $0.0001 Per Share
Security Exchange Name	NYSE
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Entity Common Stock, Shares Outstanding		70,876,222
Entity Public Float			$ 1,250,372,984
ICFR Auditor Attestation Flag	true
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the Registrant’s Definitive Proxy Statement relating to the 2021 Annual Meeting of Shareholders are incorporated by reference into Part III of this Report. The Definitive Proxy Statement will be filed within 120 days of the Registrant’s fiscal year ended December 31, 2020.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 173,415	$ 57,937
Short-term investments	555,231	130,333
Receivable from collaboration partners ($943 and $0 from a related party)	1,049	132
Accrued interest receivable	649	251
Prepaid expenses and other current assets	5,471	4,052
Total current assets	735,815	192,705
Long-term investments	6,440
Property and equipment, net	10,807	9,330
Right-of-use assets	12,781
Restricted cash	203	203
Other long-term assets	6,246	872
Total assets	772,292	203,110
Current liabilities:
Accounts payable	15,682	4,704
Accrued research and development expenses	18,307	4,572
Other accrued liabilities	9,543	4,950
Deferred revenue, current ($67,571 and $0 to a related party)	74,571	7,000
Other current liabilities	3,566	1,480
Total current liabilities	121,669	22,706
Deferred revenue, noncurrent ($117,808 and $0 to a related party)	122,830	12,022
Operating lease liabilities, noncurrent	15,243
Deferred rent, non-current		3,734
Other long-term liabilities ($9,703 and $0 to a related party)	10,246	806
Total liabilities	269,988	39,268
Commitments (Note 12)
Stockholders’ equity:
Preferred stock, $0.0001 par value, 10,000,000 shares authorized as of December 31, 2020 and 2019; no shares issued and outstanding as of December 31, 2020 and 2019	0	0
Common stock, $0.0001 par value, 400,000,000 shares authorized as of December 31, 2020 and 2019; 65,114,685 and 45,925,004 shares issued and outstanding as of December 31, 2020 and 2019, respectively	6	4
Additional paid-in capital	830,438	369,100
Accumulated deficit	(328,184)	(205,326)
Accumulated other comprehensive income	44	64
Total stockholders’ equity	502,304	163,842
Total liabilities and stockholders’ equity	$ 772,292	$ 203,110

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Related party, receivable from collaboration partners	$ 943	$ 0
Related party, deferred revenue - current	67,571	0
Related party, deferred revenue - noncurrent	117,808	0
Related party, other long-term liabilities	$ 9,703	$ 0
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	65,114,685	45,925,004
Common stock, shares outstanding	65,114,685	45,925,004

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Total collaboration and license revenues	$ 77,517	$ 15,000	$ 8,353
Operating expenses:
Research and development (($3,446), $0 and $0 from a related party)	159,348	78,481	49,646
General and administrative	42,404	25,228	13,566
Total operating expenses	201,752	103,709	63,212
Loss from operations	(124,235)	(88,709)	(54,859)
Non-operating income (expense):
Interest and other income, net	1,377	5,201	4,922
Gain on deemed sale from equity method investee	613		1,229
Share of loss from equity method investee	(613)	(1,202)	(886)
Total non-operating income, net	1,377	3,999	5,265
Net loss	(122,858)	(84,710)	(49,594)
Other comprehensive income (loss)	(20)	171	(65)
Comprehensive loss	$ (122,878)	$ (84,539)	$ (49,659)
Net loss per share, basic and diluted	$ (2.24)	$ (1.93)	$ (1.43)
Weighted-average number of shares used to compute basic and diluted net loss per share	54,787,118	43,825,991	34,618,237
License Revenue
Revenues:
Total collaboration and license revenues	$ 55,096	$ 8,000	$ 3,000
Collaboration Revenue
Revenues:
Total collaboration and license revenues	$ 22,421	$ 7,000	$ 5,353

Consolidated Statements of Op_2

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
License Revenue
Revenue from related parties	$ 55,096	$ 0	$ 0
Collaboration Revenue
Revenue from related parties	15,421	0	0
Research and Development
Reimbursement from related party for shared costs	$ (3,446)	$ 0	$ 0

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Purchase AgreementGilead	Cumulative Effect, Period of Adoption, Adjustment	Convertible Preferred Stock	Common Stock	Common StockPurchase AgreementGilead	Additional Paid-In Capital	Additional Paid-In CapitalPurchase AgreementGilead	Accumulated Deficit	Accumulated DeficitCumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2017	$ (72,328)						$ 948		$ (73,234)		$ (42)
Balance, shares at Dec. 31, 2017				30,459,574
Balance at Dec. 31, 2017				$ 226,196
Balance, shares at Dec. 31, 2017					3,278,129
Conversion of preferred stock to common stock	226,198				$ 3		226,195
Conversion of preferred stock to common stock, shares				(30,459,574)
Conversion of preferred stock to common stock				$ (226,196)
Conversion of preferred stock to common stock, shares					30,459,574
Issuance of common stock	124,735				$ 1		124,734
Issuance of common stock, shares					9,200,000
Issuance of common stock upon exercise of stock options	95						95
Issuance of common stock upon exercise of stock options, shares					67,349
Vesting of early exercised stock options and restricted stock	1,276						1,276
Vesting of early exercised stock options and restricted stock, shares					528,374
Issuance of common stock under Employee Stock Purchase Plan	751						751
Issuance of common stock under Employee Stock Purchase Plan, shares					77,397
Stock-based compensation	3,874						3,874
Other comprehensive income (loss)	(65)										(65)
Net loss	(49,594)								(49,594)
Balance at Dec. 31, 2018	234,942				$ 4		357,873		(122,828)		(107)
Balance, shares at Dec. 31, 2018					43,610,823
Issuance of common stock upon exercise of stock options	188						188
Issuance of common stock upon exercise of stock options, shares					34,780
Vesting of early exercised stock options and restricted stock	1,029						1,029
Vesting of early exercised stock options and restricted stock, shares					417,883
Issuance of common stock under Employee Stock Purchase Plan	1,029						1,029
Issuance of common stock under Employee Stock Purchase Plan, shares					148,709
Stock-based compensation	8,981						8,981
Other comprehensive income (loss)	171										171
Net loss	(84,710)								(84,710)
Balance at Dec. 31, 2019	$ 163,842				$ 4		369,100		(205,326)		64
Balance (ASC 606) at Dec. 31, 2019			$ 2,212							$ 2,212
Balance, shares at Dec. 31, 2019				0
Balance, shares at Dec. 31, 2019	45,925,004				44,212,195
Issuance of common stock	$ 326,246	$ 107,468			$ 2		326,244	$ 107,468
Issuance of common stock, shares					12,650,000	5,963,029
Issuance of common stock upon exercise of stock options, shares	392,523
Issuance of common stock upon exercise of stock options and vesting of restricted stock	$ 3,366						3,366
Issuance of common stock upon exercise of stock options and vesting of restricted stock, shares					405,752
Vesting of early exercised stock options and restricted stock	848						848
Vesting of early exercised stock options and restricted stock, shares					258,824
Issuance of common stock under Employee Stock Purchase Plan	1,587						1,587
Issuance of common stock under Employee Stock Purchase Plan, shares					202,101
Stock-based compensation	21,825						21,825
Other comprehensive income (loss)	(20)										(20)
Net loss	(122,858)								(122,858)
Balance at Dec. 31, 2020	$ 502,304				$ 6		$ 830,438		$ (328,184)		$ 44
Balance, shares at Dec. 31, 2020				0
Balance, shares at Dec. 31, 2020	65,114,685				63,691,901

Consolidated Statements of Co_2

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)shares
Offering costs	$ 21,629
Issuance of common stock	326,246
Offering cost from related party	$ 3,762
IPO
Issuance of common stock, shares | shares	2,200,000
Issuance of common stock	$ 56,738
Purchase Agreement | Gilead
Offering costs	1,931
Issuance of common stock	$ 107,468

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 flow from operating activities
Net loss	$ (122,858)	$ (84,710)	$ (49,594)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	21,825	8,981	3,874
Depreciation and amortization	3,149	3,578	3,664
Amortization of right-of-use assets	1,042
Share of loss (gain on deemed sale) from equity method investee, net		1,202	(343)
Amortization of premiums on investments	(46)	(2,638)	(1,752)
Other non-operating income			(177)
Changes in operating assets and liabilities:
Receivable from collaboration partners (($943), $0 and $0 from a related party)	(917)	(132)
Amounts owed by PACT Pharma		83	(58)
Prepaid expenses and other current assets	(838)	(1,982)	(1,180)
Other long-term assets	(5,374)	(588)	(80)
Accounts payable	9,272	1,726	(69)
Accrued research and development expenses	13,735	1,756	1,623
Other accrued liabilities	4,593	1,743	1,874
Other current liabilities		57	43
Deferred revenue ($185,379, $0 and $0 to a related party)	178,379	(2,000)	(353)
Operating lease liabilities	(993)
Deferred rent		(538)	(468)
Other long-term liabilities ($9,703, $0 and $0 to a related party)	10,201
Net cash provided by (used in) operating activities	111,170	(73,462)	(42,996)
Cash flow from investing activities
Purchases of short-term and long-term investments	(739,658)	(247,755)	(261,552)
Proceeds from maturities of short-term and long-term investments	307,343	308,892	151,855
Sales of short-term investments	1,003
Purchases of property and equipment	(3,055)	(1,925)	(3,743)
Net cash provided by (used in) investing activities	(434,367)	59,212	(113,440)
Cash flow from financing activities
Proceeds from initial public offering, net of issuance costs			125,111
Proceeds from issuance of common stock and rights to purchase additional shares ($164,207, $0 and $0 from a related party)	433,776
Proceeds from issuance of common stock pursuant to equity award plans	4,953	1,217	4,098
Repurchase of unvested shares of stock	(54)	(94)
Payment of preferred stock issuance costs			(135)
Net cash provided by financing activities	438,675	1,123	129,074
Net increase (decrease) in cash, cash equivalents and restricted cash	115,478	(13,127)	(27,362)
Cash, cash equivalents and restricted cash at beginning of period	58,140	71,267	98,629
Cash, cash equivalents and restricted cash at end of period	173,618	58,140	71,267
Supplemental disclosures:
Cash paid for amounts included in measurement of lease liabilities	2,105
Non-cash investing and financing activities:
Right-of-use assets obtained in exchange for new operating lease liabilities	8,019
Unpaid portion of financing costs included in accounts payable	61
Unpaid portion of property and equipment purchases included in accounts payable and accrued liabilities	1,583	12	136
Vesting of early exercised stock options and restricted stock	$ 848	$ 1,029	$ 1,276

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Cash Flows [Abstract]
Receivable from related party	$ 943	$ 0	$ 0
Deferred revenue from related party	185,379	0	0
Other long term liabilities from related party	$ 9,703	$ 0	$ 0

Organization

Organization	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	Note 1. Organization Description of Business Arcus Biosciences, Inc. (the Company) is a clinical-stage biopharmaceutical company focused on creating best-in-class cancer therapies. The Company’s initial focus has been on well-characterized biological pathways with significant scientific data supporting their importance. Since its inception in 2015, the Company has built a robust and highly efficient drug discovery capability to create highly differentiated small molecules, which the Company is developing in combination with its in-licensed monoclonal antibodies through rationally designed, indication-specific clinical trial designs. The Company currently has four investigational products in clinical development: domvanalimab (formerly referred to as AB154), etrumadenant (formerly referred to as AB928), AB680, and zimberelimab (formerly referred to as AB122).

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Note 2. Summary of Significant Accounting Policies Basis of Presentation The consolidated financial statements and accompanying notes have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP) and include all adjustments necessary for the fair presentation of the Company’s financial position for the periods presented. Principles of Consolidation The accompanying consolidated financial statements are comprised of Arcus Biosciences, Inc. and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, as well as related disclosure of contingent assets and liabilities. Estimates were used to determine the standalone selling price of performance obligations and the timing of revenue recognition, the value of stock-based awards and other issuances, accruals for research and development costs, useful lives of long-lived assets, and uncertain tax positions. Actual results could differ materially from the Company’s estimates. Risk and Uncertainties The Company’s future results of operations involve a number of risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of clinical trial results and achievement of milestones, uncertainty of regulatory approval of the Company’s potential drug candidates, uncertainty of market acceptance of the Company’s product candidates, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals and sole source suppliers. The Company’s investigational products require approval from the U.S. Food and Drug Administration (FDA) and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any investigational products will receive the necessary approvals. If the Company does not obtain regulatory approval and does not successfully commercialize any of its investigational products, it would have a materially adverse impact on the Company. Segments The Company operates and manages its business as one reportable and operating segment, which is the business of developing and commercializing cancer therapies. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating and evaluating financial performance. All long-lived assets are maintained in the United States of America. Cash Equivalents and Investments Cash equivalents consist of marketable securities having an original maturity of three months or less at the time of purchase. Short-term investments have maturities of greater than three months and less than twelve months at the time of purchase. Long-term investments have maturities greater than 12 months at the time of purchase. Collectively, cash equivalents, short-term and long-term investments are considered available-for-sale and are recorded at fair value. Unrealized gains and losses are recorded in accumulated other comprehensive loss. Realized gains and losses are included in interest and other income, net in the consolidated statements of operations and comprehensive loss. The basis on which the cost of a security sold or amount reclassified out of accumulated other comprehensive income into earnings is determined using the specific identification method. Reconciliation of Cash, Cash Equivalents, and Restricted Cash as Reported in Consolidated Statements of Cash Flows Restricted cash at December 31, 2020 and 2019 represents cash balances held as security in connection with the Company’s facility lease agreements. The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the consolidated balance sheets to the total shown in the consolidated statements of cash flows (in thousands): December 31, 2020 December 31, 2019 Cash and cash equivalents $ 173,415 $ 57,937 Restricted cash 203 203 Cash, cash equivalents and restricted cash $ 173,618 $ 58,140 Fair Value Measurements Fair value accounting is applied for all financial assets and liabilities, including short-term and long-term investments, and non-financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including receivable from a related party, accounts payable and accrued expenses and other current liabilities approximate fair value due to their short-term maturities. Concentration of Credit Risk Cash equivalents, short-term and long-term investments are financial instruments that potentially subject the Company to concentrations of credit risk. The Company invests in money market funds, treasury bills and notes, government bonds, commercial paper and corporate notes. The Company limits its credit risk associated with cash equivalents, short-term and long-term investments by placing them with banks and institutions it believes are highly credit worthy and in highly rated investments. Property and Equipment Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from one to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. Upon retirement or sale, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statement of operations and comprehensive loss. Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment charge would be recorded when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. Impairment, if any, is assessed using discounted cash flows or other appropriate measures of fair value. The Company did not recognize any impairment charges for the years ended December 31, 2020, 2019 and 2018. Collaborative Arrangements and Contracts with Customers The Company assesses whether its collaboration agreements are subject to Accounting Standards Codification (ASC) Topic 808, Collaborative Arrangements and whether both parties have active participation in the arrangement and are exposed to significant risks and rewards. To the extent that the arrangement falls within the scope of ASC 808, the Company applies the unit of account guidance under ASC Topic 606, Revenue from Contracts with Customers (ASC 606) , to identify distinct performance obligations, and then determine whether a customer relationship exists for each distinct performance obligation. If the Company determines a performance obligation within the arrangement is with a customer, it applies the guidance in ASC 606. If a portion of a distinct bundle of goods or services within an arrangement is not with a customer, then the unit of account is not within the scope of ASC 606, and the recognition and measurement of that unit of account shall be based on analogy to authoritative accounting literature or, if there is no appropriate analogy, a reasonable, rational, and consistently applied accounting policy election. The Company recognizes revenue when its customer obtains control of promised goods or services in a contract for an amount that reflects the consideration the Company expects to receive in exchange for those goods or services. For contracts with customers, the Company performs The estimation of the stand-alone selling price may include such estimates as forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if they can be satisfied at a point in time or over time, and the Company measures the services delivered to the customer, which are periodically reviewed based on the progress of the related program. The effect of any change made to an estimated input component and, therefore revenue or expense recognized, would be recorded as a change in estimate. In addition, variable consideration (e.g. milestone payments) must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. The Company enters into collaborative arrangements that typically include one of more of the following: (i) license fees; (ii) milestone payments related to the achievement of developmental, regulatory, or commercial goals; (iii) royalties on net sales of licensed products; (iv) fees attributable to options to intellectual property; and (v) cost-sharing or research and development (R&D) funding arrangements. When a portion of non‑refundable upfront fees or other payments received are allocated to continuing performance obligations under the terms of a collaborative arrangement, they are recorded as deferred revenue and recognized as revenue when (or as) the underlying performance obligation is satisfied. Fees attributable to options are deferred until the option expires or is exercised. The Company classifies contract liabilities as current when it expects to satisfy its performance obligations within one year, and noncurrent when the Company expects to satisfy those performance obligations in greater than one year. When an option is exercised, the performance obligations associated with the option are identified, which will determine the accounting for the transaction price attributable to the option. As part of the accounting for these arrangements, the Company must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation which determines how the transaction price is allocated among the performance obligation. To determine the stand-alone selling price, the Company may consider items such as forecasted revenues, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if it can be satisfied at a point in time or over time. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. License Fees If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, upfront fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments and Variable Consideration At the inception of each arrangement that includes milestone payments or variable consideration, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated value is included in the transaction price. Milestone payments that are not within the control of the Company or the Company’s collaboration partner, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration or other revenues and earnings in the period of adjustment. Cost-Sharing or R&D Funding Arrangements Under certain collaborative arrangements, the Company has been reimbursed for a portion of its research and development expenses, including costs of drug supplies. When these R&D services are performed under a reimbursement or cost sharing model with a collaboration partner, the Company records these reimbursements as a reduction of R&D expense in its consolidated statements of operations. Royalties For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its collaborative arrangements. Research and Development Expenses Research and development costs are expensed as incurred. Research and development expenses consist primarily of personnel costs for the Company’s research and development employees, costs incurred to third-party service providers for the conduct of research, preclinical and clinical studies, laboratory supplies and equipment maintenance costs, consulting and other related expenses. Also included are payments under collaborative arrangements, including up-front and milestone payments, license and option fees and expense reimbursements to the collaboration partners, as well as non-personnel costs such as professional fees payable to third parties for preclinical and clinical studies and research services, laboratory supplies and equipment maintenance, product licenses, and other consulting costs. The Company estimates research, preclinical and clinical service organizations, based on services performed, pursuant to contracts with third-party research and development organizations that conduct and manage research, preclinical and clinical activities on its behalf. Most of the Company’s clinical studies are performed by third-party contract research organizations (CROs), and as a result clinical study costs are a significant component of research and development expenses. The Company estimates these expenses based on discussions with internal management personnel and external service providers as to the progress or stage of completion of services and the contracted fees to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. Payments associated with licensing agreements to acquire licenses to develop, use, manufacture and commercialize products that have not reached technological feasibility and do not have alternative future use are expensed as incurred. Payments made to third parties under these arrangements in advance of the performance of the related services by the third parties are recorded as prepaid expenses until the services are rendered. Leases and Rent Expense The Company leases laboratory and office space in an office park in Hayward, California under a non-cancelable operating lease with terms that expire from 2025 to 2029, subject to options for the Company to extend the lease term. The Company also leases space in Brisbane, California under a non-cancelable operating lease that is expected to commence in 2021 and extend through 2031. Prior to January 1, 2020, the Company recognized related rent expense on a straight-line basis over the term of the lease. Incentives granted under the Company’s facilities lease, including allowances for leasehold improvements and rent holidays, were recognized as reductions to rental expense on a straight-line basis over the term of the lease. Deferred rent consisted of the difference between cash payments and the rent expense recognized. Subsequent to the adoption of the new leasing standard on January 1, 2020, the Company recognizes a lease asset for its right to use the underlying asset and a lease liability for the corresponding lease obligation. The Company determines whether an arrangement is or contains a lease at contract inception. Operating leases are included in operating lease right-of-use assets, other accrued liabilities, and operating lease liabilities, noncurrent in our consolidated balance sheet at December 31, 2020. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the net present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date. The incremental borrowing rate represents the interest rate the Company would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of a lease. The Company considers a lease term to be the noncancelable period that it has the right to use the underlying asset, including any periods where it is reasonably assured the Company will exercise the option to extend the contract. Periods covered by an option to extend are included in the lease term if the lessor controls the exercise of that option. The Company elected to not apply the recognition requirements of the new leasing standard to short-term leases with terms of 12 months or less which do not include an option to purchase the underlying asset that the Company is reasonably certain to exercise. For short-term leases, lease payments are recognized as operating expenses on a straight-line basis over the lease term. Stock-Based Compensation The Company accounts for stock-based compensation arrangements in accordance with ASC 718, Stock Compensation Equity Based Payments to Non-Employees No. 2018-07 (Topic 718), Compensation – Stock Compensation, Stock-based awards granted include stock options and restricted stock units (RSUs). Accounting standards require the recognition of compensation expense, using a fair value-based method, for costs related to all stock-based payments. The Company’s determination of the fair value of stock options with time-based vesting on the date of grant utilizes the Black-Scholes option-pricing model, and is impacted by the Company’s common stock price as well as other variables including, but not limited to, expected term that options will remain outstanding, expected common stock price volatility over the term of the option awards, risk-free interest rates and expected dividends. Compensation expense associated with restricted stock units is based on the fair value of common stock on the date of the grant. The fair value of a stock-based award is recognized over the period during which an optionee is required to provide services in exchange for the option award, known as the requisite service period (usually the vesting period) on a straight-line basis. Stock-based compensation expense is recognized based on the fair value determined on the date of grant and is reduced for forfeitures as they occur. Estimating the fair value of equity-settled awards as of the grant date using valuation models, such as the Black-Scholes option pricing model, is affected by assumptions regarding a number of complex variables. Changes in the assumptions can materially affect the fair value and ultimately how much stock-based compensation expense is recognized. These inputs are subjective and generally require significant analysis and judgment to develop. Income Taxes The Company provides for income taxes under the asset and liability method. Current income tax expense or benefit represents the amount of income taxes expected to be payable or refundable for the current year. Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and tax bases of assets and liabilities and net operating loss and credit carryforwards, and are measured using the enacted tax rates and laws that will be in effect when such items are expected to reverse. Deferred income tax assets are reduced, as necessary, by a valuation allowance when management determines it is more likely than not that some or all of the tax benefits will not be realized. The Company accounts for uncertain tax positions in accordance with ASC 740-10, Accounting for Uncertainty in Income Taxes. The Company includes any penalties and interest expense related to income taxes as a component of other expense and interest income, net, as necessary. On March 18, 2020, the Families First Coronavirus Response act (FFCR Act), and on March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (CARES Act) were each enacted in response to the COVID-19 pandemic. The FFCR Act and the CARES Act contain numerous tax-related provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. On June 29, 2020 California State Assembly Bill 85 (the Trailer Bill) was enacted which suspends the use of California net operating loss (NOL) deductions and limits the use of certain tax credits, including research and development tax credits, for the 2020, 2021, and 2022 tax years. The FFCR Act, CARES Act and Trailer Bill did not have a material impact on the Company’s consolidated financial statements as of December 31, 2020; however, the Company continues to examine the impacts the FFCR Act, CARES Act and Trailer Bill may have on its business, results of operations, financial condition and liquidity. Comprehensive Loss Comprehensive loss includes net loss and net unrealized income and losses on available-for-sale securities, which are presented in a single continuous statement. Other comprehensive income (loss) is also disclosed in the consolidated balance sheets and statements of stockholders’ equity in accumulated other comprehensive income (loss), and is stated net of related tax effects, if any. Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. The Company excludes the weighted-average shares subject to repurchase from its calculation of weighted average of common shares outstanding. For purposes of the diluted net loss per share calculation, outstanding common stock options are considered to be potentially dilutive securities. Because the Company reported a net loss for the years ended December 31, 2020, 2019 and 2018, and the inclusion of the potentially dilutive securities would be antidilutive, diluted net loss per share is the same as basic net loss per share for all periods. Recently Adopted Accounting Standards In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes In November 2018, the FASB issued ASU No. 2018-18 (Topic 808), Collaborative Arrangements Revenue from Contracts with Customers (Topic 606) In August 2018, the FASB issued ASU No.2018-13 (Topic 820), Fair Value Measurement. In August 2018, the FASB issued ASU No.2018-15 (Subtopic 350-40), Intangibles – Goodwill and Other – Internal-Use Software. In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases No. 2018-10 Codification Improvements to Topic 842, Leases No. 2018-11, Leases (Topic 842): Targeted Improvements The Company adopted this standard on January 1, 2020 using the modified retrospective approach and elected the package of practical expedients permitted under transition guidance, which allowed the Company to carry forward its historical assessments of: 1) whether contracts are or contain leases, 2) lease classification and 3) initial direct costs. The Company did not elect the practical expedient allowing the use-of-hindsight which would require the Company to reassess the lease term of its leases based on all facts and circumstances through the effective date and did not elect the practical expedient pertaining to land easements as this is not applicable to the current contract portfolio. The Company elected the post-transition practical expedient to not separate lease components from nonlease components for all existing lease classes. The Company also elected a policy of not recording leases on its consolidated balance sheets when the leases have a term of 12 months or less and the Company is not reasonably certain to elect an option to purchase the leased asset. The adoption of this standard resulted in the recognition of a right-of-use (ROU) asset of $5.8 million and lease liabilities of $10.1 million, comprised of $1.2 million and $8.9 million of current and noncurrent liabilities, respectively. The adoption also resulted in the derecognition of the deferred rent balance of $4.3 million as of January 1, 2020. The adoption of the standard had no impact on the Company’s consolidated statements of operations and comprehensive loss or to its cash flows from or used in operating, financing, or investing activities on its consolidated statements of cash flows. No cumulative-effect adjustment within accumulated deficit was required to be recorded as a result of adopting this standard. In June 2016, the FASB issued ASU No. 2016 -13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments The Company adopted this standard on January 1, 2020 using the modified retrospective approach. The Company adopted this ASU as of January 1, 2020 with an immaterial impact on its financial statements.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 3. Fair Value Measurements Financial assets and liabilities are recorded at fair value. The accounting guidance for fair value provides a framework for measuring fair value, clarifies the definition of fair value and expands disclosures regarding fair value measurements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The accounting guidance establishes a three-tiered hierarchy, which prioritizes the inputs used in the valuation methodologies in measuring fair value as follows: Level 1—Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2—Inputs (other than quoted market prices included in Level 1) are either directly or indirectly observable for the asset or liability through correlation with market data at the measurement date and for the duration of the instrument’s anticipated life. Level 3—Inputs reflect management’s best estimate of what market participants would use in pricing the asset or liability at the measurement date. Consideration is given to the risk inherent in the valuation technique and the risk inherent in the inputs to the model. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. During the periods presented, the Company has not changed the manner in which it values assets and liabilities that are measured at fair value. The Company recognizes transfers between levels of the fair value hierarchy as of the end of the reporting period. There were no transfers within the hierarchy during the years ended December 31, 2020 and 2019. The following tables set forth the Company’s financial instruments (excluding restricted cash) that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): December 31, 2020 Total Level 1 Level 2 Level 3 Money market funds $ 146,468 $ 146,468 $ - $ - U.S. treasury securities 301,112 - 301,112 - U.S. government agency obligations 25,001 - 25,001 - Corporate securities and commercial paper 262,505 - 262,505 - Total assets measured at fair value $ 735,086 $ 146,468 $ 588,618 $ - December 31, 2019 Total Level 1 Level 2 Level 3 Money market funds $ 45,498 $ 45,498 $ - $ - U.S. treasury securities 74,854 - 74,854 - Corporate securities and commercial paper 67,918 - 67,918 - Total assets measured at fair value $ 188,270 $ 45,498 $ 142,772 $ - Classified as (with contractual maturities): Year Ended December 31, 2020 2019 Cash and cash equivalents $ 173,415 $ 57,937 Short-term investments (due within one year) 555,231 130,333 Long-term investments (due between one and two years) 6,440 - $ 735,086 $ 188,270 The investments are classified as available-for-sale marketable securities. At December 31, 2020 and 2019, the balance in the Company’s accumulated other comprehensive loss comprised activity related to the Company’s available-for-sale marketable securities. There were immaterial realized gains recognized on the sale of available-for-sale marketable securities during the year ended December 31, 2020 and none during the years ended December 31, 2019 and 2018, respectively. As a result, the Company did not reclassify any amounts out of accumulated other comprehensive loss for the periods then ended. The Company has a limited number of available-for-sale marketable securities in loss positions as of December 31, 2020, which the Company does not intend to sell and has concluded it will not be required to sell before recovery of the amortized cost for the investment at maturity. The fair value and amortized cost of investments in marketable securities by major security type as of December 31, 2020 and 2019 are presented in the tables that follow (in thousands): Amortized Cost Unrealized Gain Unrealized Loss Fair Value As of December 31, 2020: Money market funds $ 146,468 $ - $ - $ 146,468 U.S. treasury securities 301,075 38 (1 ) 301,112 U.S. government agency obligations 24,997 4 - 25,001 Corporate securities and commercial paper 262,502 15 (12 ) 262,505 Total $ 735,042 $ 57 $ (13 ) $ 735,086 Amortized Cost Unrealized Gain Unrealized Loss Fair Value As of December 31, 2019: Money market funds $ 45,498 $ - $ - $ 45,498 U.S. treasury securities 74,801 12 (1 ) 74,812 Corporate securities and commercial paper 67,907 55 (2 ) 67,960 Total $ 188,206 $ 67 $ (3 ) $ 188,270

Consolidated Balance Sheet Comp

Consolidated Balance Sheet Components	12 Months Ended
	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Consolidated Balance Sheet Components	Note 4. Consolidated Balance Sheet Components Property and Equipment Property and equipment, net consisted of the following (in thousands): As of December 31, 2020 2019 Scientific equipment $ 9,902 $ 8,168 Furniture and equipment 1,521 1,165 Capitalized software 225 146 Leasehold improvements 11,111 10,834 Construction in progress 2,336 238 Total 25,095 20,551 Less: Accumulated depreciation and amortization (14,288 ) (11,221 ) Property and equipment, net $ 10,807 $ 9,330 Other Accrued Liabilities Other accrued liabilities consisted of the following (in thousands): As of December 31, 2020 2019 Accrued personnel expenses 8,632 $ 4,571 Professional fees 295 183 Other 616 196 Total other accrued liabilities $ 9,543 $ 4,950

Equity Investment in PACT Pharm

Equity Investment in PACT Pharma	12 Months Ended
	Dec. 31, 2020
Equity Method Investment [Abstract]
Equity Investment in PACT Pharma	Note 5: Equity Investment in PACT Pharma The Company owns approximately 3.6 million shares of common stock, 1.0 million shares of Series A preferred stock, and warrants to purchase additional stock of PACT Pharma, Inc. (PACT Pharma), a privately funded, early-stage biopharmaceutical company focused on adoptive cell therapy. This interest in PACT Pharma is accounted for as an equity method investment, and as a result the Company records its share of PACT Pharma’s operating results in interest and other income, net, in its condensed consolidated statements of operations and comprehensive income (loss). The investment balance was zero at December 31, 2020 and December 31, 2019. Since the Company has no obligation to provide cash financing to PACT Pharma, the Company is not required to record losses beyond the carrying amount of the investment. In January and June 2020, PACT Pharma issued shares in its Series C and Series C-1 preferred stock financings. The Company did not participate in these financings. The decrease in the Company’s equity ownership percentage and an increase in PACT Pharma’s estimated fair value per share resulted in gains on dilution totaling $2.0 million during the year ended December 31, 2020. After applying $1.4 million in losses accumulated in prior periods when the equity investment balance was zero, the Company recorded a gain of $0.6 million for the year ended December 31, 2020. There were no gains recorded by the Company for the year ended December 31, 2019. The Company’s share of PACT Pharma’s losses for the year ended December 31, 2020 exceeded gains for the same period. The Company recorded $0.6 million and $1.2 million for its share of PACT Pharma’s operating losses for the years ended December 31, 2020 and 2019, respectively. The unrecognized equity method losses in excess of the Company’s investment was $1.3 million as of December 31, 2020. For the years ended December 31, 2020 and 2019, the Company determined the fair value of the warrants to be insignificant to the consolidated financial statements.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	Note 6. Leases The Company leases its corporate headquarters, which includes approximately 136,293 square feet of executive offices and research and development and business operations, in an office park in Hayward, California under a non-cancelable operating lease with terms that expire from 2025 to 2029, subject to options by the Company to extend the lease term. The Company also leases space in Brisbane, California under a non-cancelable operating lease that is expected to commence in 2021 and extend through 2031. In June 2020, the Company entered into a lease amendment for 36,303 square feet of additional space in Hayward, California, that is expected to commence during 2021 for an eight-year In December 2020, the Company entered into a lease agreement for 109,237 square feet of space in Brisbane, California, that is expected to commence in the second half of 2021 for a term of approximately ten years with undiscounted minimum lease payments totaling approximately $90.3 million. The lease is subject to two options to extend the lease term for a period of eight years each. The lease agreement includes an allowance of approximately $12.6 million for tenant improvements with an option to increase the allowance by $5.5 million. The space was under construction at December 31, 2020 and has not been delivered to the Company. At December 31, 2020 the Company’s lease portfolio had a weighted average remaining term of 6.2 years. The leases require monthly lease payments that are subject to annual increases throughout the lease term. The optional period has not been considered in the determination of the right-of-use assets or lease liabilities associated with this lease as the Company did not consider it reasonably certain it would exercise the option. The Company cannot determine the implicit rate in its leases, and therefore the Company uses its incremental borrowing rate as the discount rate when measuring operating lease liabilities. The incremental borrowing rate represents an estimate of the interest rate the Company would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of a lease within a particular currency environment. The Company used an incremental borrowing rate of 10% as of the date of adoption for leases that commenced prior to January 1, 2020. The weighted average discount rate for the Company’s lease portfolio at December 31, 2020 was 7.3%. For the year ended December 31, 2020, the Company incurred $2.7 million of lease costs included in operating expenses in the consolidated statements of income and comprehensive income in relation to its operating lease, a portion of which was variable rent expense and not included within the measurement of the Company’s operating ROU assets and lease liabilities. The variable rent expense consists primarily of the Company’s proportionate share of operating expenses, property taxes, and insurance and is classified as lease expense due to the Company’s election to not separate lease and non-lease components. Rent expense was $1.6 million for each of the years ended December 31, 2019 and 2018. As of December 31, 2020, the Company’s future minimum lease payments were as follows (in thousands): Year Ended December 31, 2020 (1) 2019 (2) 2020 - 2,105 2021 4,041 2,195 2022 3,409 2,265 2023 3,522 2,339 2024 3,640 2,415 2025 3,340 2,072 Thereafter 4,311 - Total undiscounted future minimum lease payments 22,263 13,391 Less: Imputed interest (4,153 ) N/A Total operating lease liabilities 18,110 N/A Less: Current portion of operating lease liabilities (included in other current liabilities) (2,867 ) N/A Operating lease liabilities, noncurrent 15,243 N/A (1) Presented in accordance with ASC 842. (2) Presented in accordance with ASC 840. N/A items not required under ASC 840. Total undiscounted future minimum lease payments do not include approximately $90.3 million related to the Company’s Brisbane lease that has not yet commenced. This lease is expected to commence during 2021 with a lease term of approximately 10 years. Total minimum lease payments have not been reduced by minimum sublease rent income of approximately $0.1 million under a noncancelable sublease. The Company has provided deposits for letters of credit totaling $0.2 million to secure its obligations under its lease, which have been classified as long-term assets on the Company’s consolidated balance sheet as of December 31, 2020.

License and Collaboration Agree

License and Collaboration Agreements	12 Months Ended
	Dec. 31, 2020
License And Collaboration Agreements [Abstract]
License and Collaboration Agreements	Note 7. License and Collaboration Agreements The following table summarizes the revenues received as a result of the Company’s collaboration agreements with Gilead Sciences, Inc. (Gilead) and Taiho Pharmaceutical Co., Ltd. (Taiho): Year Ended December 31, 2020 2019 2018 License revenue $ 55,096 $ 8,000 $ 3,000 Collaboration revenue 22,421 7,000 5,353 Collaboration and license revenue $ 77,517 $ 15,000 $ 8,353 The following table summarizes details of revenues by collaboration and by category of revenue: Year Ended December 31, Revenues recognized: Over time Point in time 2020 2019 2018 Gilead license to zimberelimab * $ 55,096 $ - $ - Gilead access rights related to the Company's research and development pipeline * 15,421 - - Taiho license to zimberelimab * - 8,000 - Taiho license to etrumadenant * - - 3,000 Taiho collaboration agreement * 7,000 7,000 5,353 Total collaboration and license revenue $ 77,517 $ 15,000 $ 8,353 The Company recognized the following revenue as a result of changes in the deferred revenue balance during the period below (in thousands): Year Ended December 31, Revenue recognized in the period from: 2020 2019 2018 Amounts included in deferred revenue at the beginning of the period $ 7,000 $ 7,000 $ 5,353 Performance obligations satisfied in previous period - - - The Company received $175 million in upfront payments from Gilead in connection with the Option, License and Collaboration Agreement and identified $100 million in unconstrained consideration to be received in 2022. In addition, the Company received $200 million from Gilead in connection with the Stock Purchase Agreement, of which approximately $109.4 million represented the fair value of stock purchased at the transaction closing date in July 2020 with the remaining premium of $90.6 million allocated to the transaction price. At the transaction closing date, these payments were allocated to the performance obligations identified as follows: Amount Allocation of transaction price Upfront cash consideration $ 175,000 Payment for access rights related to the Company's research and development pipeline 100,000 Premium from Stock Purchase Agreement 90,600 Total transaction price allocated to revenue $ 365,600 Allocation to performance obligations Zimberelimab license $ 55,096 Etrumadenant option 126,960 Domvanalimab option 36,728 Access rights related to the Company's research and development pipeline 137,113 Development and commercialization services for zimberelimab 9,703 Total $ 365,600 Gilead Sciences, Inc. On May 27, 2020, the Company entered into an Option, License and Collaboration Agreement (Gilead Collaboration Agreement), Common Stock Purchase Agreement (the Stock Purchase Agreement), and Investor Rights Agreement, (collectively, the Gilead Agreements), each with Gilead Sciences, Inc. (Gilead). The transaction closed on July 13, 2020 following expiration of the antitrust waiting period. Upon closing, Gilead made an upfront payment of $175 million pursuant to the Gilead Collaboration Agreement, and made an equity investment of approximately $200 million in the Company by purchasing 5,963,029 shares of Arcus common stock at a per share price of $33.54 pursuant to the Stock Purchase Agreement, and the Company appointed Gilead’s designee, Merdad Parsey, M.D., Ph.D. and Michael Quigley, Ph.D., to the Company’s Board of Directors pursuant to the Investor Rights Agreement. Pursuant to the terms of the Gilead Collaboration Agreement, Gilead has an exclusive license to develop and commercialize zimberelimab in certain markets and obtained exclusive options to acquire an exclusive license to develop and commercialize all of the Company’s current and future clinical programs during the 10-year collaboration term, contingent upon Gilead’s access rights payments of up to $400 million and, for those programs that enter clinical development prior to the end of the collaboration term, for up to an additional three years thereafter. Gilead may exercise its option, on a program-by-program basis, upon payment of an option fee that ranges from $200 million to $275 million per program for the Company’s clinical programs in existence at the date of the agreement, and $150 million per program for all other programs that enter clinical development thereafter should Gilead elect to exercise its options. Upon Gilead’s exercise of its option to a program, the two companies will co-develop and equally share global development costs, subject to certain opt-out rights of the Company, and expense caps on the Company’s spending and related subsequent adjustments. For each optioned program, provided the Company has not exercised its opt-out rights, the Company has an option to co-promote in the United States with equal sharing of related profits and losses. Gilead has the right to exclusively commercialize any optioned programs outside of the U.S., subject to the rights of the Company’s existing partners to any territories, and Gilead will pay to the Company tiered royalties as a percentage of revenues ranging from the high teens to the low twenties. Gilead will further provide ongoing research and development support in the form of research and development pipeline access rights payments of up to $400 million over the collaboration term. Pursuant to the Stock Purchase Agreement and the Investor Rights Agreement, Gilead has the right, at its option, to purchase additional shares from the Company, up to a maximum of 35% of the Company’s then-outstanding voting common stock, from time to time over the next five years, at a purchase price equal to the greater of a 20% premium to market (based on a trailing five-day The Company’s assessment of the transaction price included an analysis of amounts it expected to receive, which at contract inception consisted of the upfront cash payment of $175.0 million due upon contract closing in July 2020, the $100.0 million payment related to the research and development access rights due in 2022, and the $90.6 million premium resulting from Gilead’s purchase of common stock. All payments to date have been made by Gilead as they became due and payable so given this successful collection history, the Company considers the entire $365.6 million outlined above to be the initial transaction price. The Company evaluated the Gilead Agreements under ASC 606 and determined that the performance obligations at the contract inception consisted of the following: Zimberelimab license Effective on closing, Gilead obtained an exclusive license to zimberelimab. The standalone selling price of this license was determined using a discounted cash flow method. The Company recognized the full revenues associated with this performance obligation on the date the transaction closed. Etrumadenant option Gilead has the right to exercise an option for exclusive rights to etrumadenant, the Company’s adenosine receptor program, in exchange for an option payment of $250.0 million, that expires after a proscribed period following the Company’s achievement of certain development milestones. The Company calculated the standalone selling price of this program using a discounted cash flow method and concluded that it exceeded the price of the option, creating a material right and a distinct performance obligation. If the option is exercised, the performance obligations associated with the option will be identified and will determine the accounting for the option’s transaction price. If the option is allowed to lapse after development milestones trigger the start of the opt-in period, the Company will recognize any deferred revenue allocated to the option at the time of the lapse. At December 31, 2020, the Company had $127.0 million of deferred revenue on its consolidated balance sheets related to this performance obligation. The Company has evaluated the program’s status as of the balance sheet date and believes that some or all of the revenue associated with the opt-in will be recognized within the minimum four-year Domvanalimab option Gilead has the right to exercise an option for exclusive rights to domvanalimab, the Company’s anti-TIGIT monoclonal antibody, in exchange for an option payment of $275.0 million, that expires after a proscribed period following the Company’s achievement of certain development milestones. The Company calculated the standalone selling price of this program using a discounted cash flow method and concluded that it exceeded the price of the option, creating a material right and a distinct performance obligation. If the option is exercised, the performance obligations associated with the option will be identified and will determine the accounting for the option’s transaction price. If the option is allowed to lapse after development milestones trigger the start of the opt-in period, the Company will recognize any deferred revenue allocated to the option at the time of the lapse. At December 31, 2020, the Company had $36.7 million of deferred revenue on its consolidated balance sheets related to this performance obligation. The Company has evaluated the program’s status and believes that revenue associated with the opt-in will be recognized within one year. Access rights related to the Company’s research and development pipeline Gilead receives exclusive access to the Company’s current programs as well as the future programs for a period of ten years, contingent upon Gilead’s payment of $400 million, with the first payment of $100.0 million in 2022, and an additional $100 million payment due at Gilead’s option on each of the fourth, sixth, and eighth anniversaries of the agreement. The standalone selling price of this ongoing research and development pipeline access was determined using an expected cost-plus margin approach. The Company evaluated its rights and obligations in the Gilead Collaboration Agreement and determined that Gilead is contractually obligated to make the $100.0 million payment due in 2022 resulting in a minimum term of four years for this performance obligation. As a result, the amount was included in the transaction price. The Company uses a time-elapsed input method to measure progress toward satisfying this obligation, which is the method the Company believes most faithfully depicts the Company’s performance in transferring the promised services during the time period in which Gilead has access to the Company’s research and development pipeline. Accordingly, the revenue allocated to the performance obligation is being recognized using this input method over the minimum four-year At December 31, 2020 the Company had $121.7 million of deferred revenue on its consolidated balance sheets related to this performance obligation, classified between current and noncurrent based on the amortization of the revenue. Development and commercialization services for zimberelimab In conjunction with the license, the Company determined there existed a separate obligation to perform further development and commercialization services for Gilead. The standalone selling price of this obligation was determined using an expected cost-plus margin approach. This obligation includes a 50/50 share of the costs associated with all future development and commercialization of zimberelimab. The portion of the transaction price allocated to this performance obligation has been allocated in accordance with the total costs forecast for the development and commercialization of zimberelimab. The Company will recognize the amounts allocated to these services as the performance obligation is satisfied . Any additional payments received from or payments made to Gilead for the 50/50 cost share will be recognized as a reduction or an increase to R&D expense, respectively. Gilead was also granted option rights to programs not yet in development. These programs were not determined to be performance obligations at contract inception, as there are no identified programs, revenues, or costs to compare against the option price. At December 31, 2020 the Company had $9.7 million of contract liabilities on its consolidated balance sheets related to this performance obligation. The Company has evaluated the program’s status and believes that revenue associated with these services will be recognized over the full term of the contract, beginning in 2021. Prepaid expenses and contract liabilities The Company incurred $7.3 million in expenses to obtain the contract, which consisted of consultant and legal fees that were directly connected to the successful completion of the Gilead Agreements. The Company determined that $1.9 million of these expenses were related to the Stock Purchase Agreement and recorded them as offering costs. The Company allocated the remaining expenses between the various performance obligations, to be recognized when the underlying revenue is recognized. The portion allocated to the delivery of zimberelimab was recognized immediately, and the portion allocated to the remaining performance obligations will be recognized with timing consistent with the associated performance obligation. During the year ended December 31, 2020, the Company recognized $0.2 million in expense from the amortization of these assets. As of December 31, 2020, the Company had $4.2 million in prepaid expenses from costs to obtain the Gilead Agreements, of which $1.0 million was recorded in prepaid expenses and other current assets and $3.2 million was recorded in other long-term assets. The Company also recognized $9.7 million in contract liabilities for future development and commercialization services which Gilead prepaid, recorded in other non-current liabilities on the consolidated balance sheets. Taiho Pharmaceutical Co., Ltd In September 2017, the Company and Taiho entered into an option and license agreement (the Taiho Agreement) to collaborate on the potential development and commercialization of certain investigational products from the Company’s portfolio in Japan and certain other territories in Asia (excluding China) (the Taiho Territory). The Taiho Agreement provides Taiho with exclusive options, over a five-year In consideration for the exclusive options and other rights contained in the Taiho Agreement, Taiho agreed to make non-refundable, non-creditable cash payments to the Company totaling $35.0 million, of which the Company received $25.0 million during 2017. An additional $5.0 million was received in 2018 and the remaining $5.0 million was received in 2019. In the event that the Company has not initiated IND enabling studies for at least five Arcus Programs prior to the expiration of the Option Period, Taiho may elect to extend the Option Period, up to a maximum of seven years, subject to an extension fee. For each option that Taiho elects to exercise, they will be obligated to make an option exercise payment of between $3.0 million to $15.0 million, depending on the development stage of the applicable Arcus Program for which the option is exercised. In addition, the Taiho Agreement provides that the Company is eligible to receive additional clinical and regulatory milestones totaling up to $130.0 million per Arcus Program, and it will be eligible to receive contingent payments of up to $145.0 million per Arcus Program associated with the achievement of specified levels of Taiho net sales in the Taiho Territory. In addition, the Company will receive royalties ranging from high single-digits to mid-teens on net sales of licensed products in the Taiho Territory. Royalties will be payable on a licensed product-by-licensed product and country-by-country basis during the period of time commencing on the first commercial sale of a licensed product in a country and ending upon the later of: (a) ten (10) years from the date of first commercial sale of such licensed product in such country; and (b) expiration of the last-to-expire valid claim of the Company’s patents covering the manufacture, use or sale or exploitation of such licensed product in such country (the Royalty Term). The Company evaluated the Taiho Agreement under ASC 606 and determined that the current performance obligations consist of (1) the research and development services, in which the Company will use commercially reasonable efforts to initiate IND enabling studies for at least five Arcus Programs, as well as further develop such Arcus Programs during the term of the Agreement, and (2) the obligation to participate on the joint steering committee. These deliverables are non-contingent in nature. The Company determined that the obligation to participate in the joint steering committee does not have stand-alone value to Taiho because the committee’s primary purpose is to monitor and govern the research and development activities and, hence, it is inseparable from the research and development services. The Company’s assessment of the transaction price included an analysis of amounts it expected to receive, which at contract inception consisted of the upfront cash payment of $20.0 million due upon contract execution in September 2017, a $5.0 million payment due within 30 days of contract execution, an anniversary payment of $5.0 million due in 2018, and a final anniversary payment of $5.0 million due in 2019. All payments were made by Taiho as they became due and payable so given this successful collection history, the Company considers the entire $35.0 million in non-refundable fees to be the initial transaction price. The Company determined that the combined performance obligation of the research and development services and the obligation to participate on the joint steering committee are satisfied over time. The Company uses a time-elapsed input method to measure progress toward satisfying its performance obligation, which is the method the Company believes most faithfully depicts the Company’s performance in transferring the promised services during the time period in which Taiho has access to the Company’s research and development activities. Accordingly, the transaction price of $35.0 million is being recognized using this input method over the estimated performance period of five years. The Company also concluded that, at the inception of the agreement, Taiho’s exclusive options are not considered material rights as the options do not contain a significant and incremental discount. The Company therefore excludes the exclusive options from the initial transaction price and accounts for them as separate contracts. In 2018, Taiho exercised its option to the Company’s adenosine receptor antagonist program, including etrumadenant, for a fee of $3.0 million, which was recognized by the Company as revenue during the year ended December 31, 2018 under Topic 605. The adoption of Topic 606 in 2019 had no effect on the revenue recognized for this fee. In 2019, Taiho exercised its option to the Company’s anti-PD-1 antibody program, including zimberelimab for a fee of $8.0 million. The Company identified one performance obligation comprised of the delivery of the license, which was completed in 2019. The transaction price was determined to be the payment of $8.0 million, which was recognized by the Company as licensing revenue during the year ended December 31, 2019 under Topic 606. Upon the option exercises, Taiho gained sole responsibility for the development and commercialization of the licensed products from within the programs in the Taiho Territory. The Company also determined that the clinical and regulatory milestone payments under the Taiho Agreement are variable consideration under Topic 606 which need to be added to the transaction price when it is probable that a significant revenue reversal will not occur. Based on the nature of the clinical and regulatory milestones, such as the regulatory approvals which are not within the Company’s control, the Company will not consider achievement of such milestones to be probable until the uncertainty associated with the milestones has been resolved. When it is probable that a significant reversal of revenue will not occur, the milestone payment will be added to the transaction price, which will then be allocated to each performance obligation, on a relative standalone selling price basis, for which the Company recognizes revenue. The Company also considers the contingent payments due from Taiho upon the achievement of specified sales volumes to be similar to royalty payments. The Company considers the license to be the predominant item to which the royalties relate. The Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). As of December 31, 2020, no sales milestone or royalty revenue has been recognized. The Taiho Agreement shall remain in effect until expiry of all Royalty Terms for the licensed products, in each case subject to certain exceptions. During the years ended December 31, 2020 and 2019, the Company recognized a total of $7.0 million and $15.0 million of revenue, respectively, under the Taiho Agreement in accordance with Topic 606. During the year ended December 31, 2018, the Company recognized a total of $8.3 million in revenue in accordance with Topic 605. Revenues for each of these years consisted of revenue recognized for the option exercised and the non-refundable upfront research and development fees. As of December 31, 2020, the Company recorded deferred revenue, current and deferred revenue, noncurrent of $7.0 million and $5.0 million, respectively, in its consolidated balance sheet. As of December 31, 20 19 , the Company recorded deferred revenue, current and deferred revenue, noncurrent of $ 7.0 million and $ 12.0 million, respectively, in its consolidated balance sheet. WuXi Biologics License Agreements The Company entered into a license agreement (the WuXi PD-1 Agreement) with WuXi Biologics in August 2017, as subsequently amended in June 2019, in which it obtained an exclusive license to develop, use, manufacture, and commercialize products including an anti-PD-1 antibody worldwide except for Greater China and Thailand. During the years ended December 31, 2020 and 2019, the Company made milestone payments of $5.0 million and $7.5 million, respectively, and incurred sub-license fees of $10.1 million and $1.2 million, respectively, under the WuXi PD-1 Agreement. These milestone payments and sub-license fees were recorded as research and development expense, as the products had not reached technological feasibility and did not have alternative future use. During the year ended December 31, 2018, the Company incurred zero expense for milestone payments and incurred zero expense for sub-license fees. The WuXi PD-1 Agreement also provides for clinical and regulatory milestone payments, commercialization milestone payments of up to $375.0 million and tiered royalty payments to be made to WuXi Biologics that range from the high single-digits to low teens of net sales by the Company of licensed products. In December 2020, the Company entered into a separate license agreement (the WuXi CD-39 Agreement) with WuXi to develop anti-CD39 antibodies. Under the agreement, the Company was granted exclusive worldwide rights to anti-CD39 antibodies discovered under the collaboration and will be responsible for the further development and commercialization of those antibodies. Upon signing the agreement, the Company incurred and paid a $0.5 million upfront payment which was recorded in R&D expense, as the products are still in research stage. The WuXi CD-39 Agreement provides for clinical and regulatory milestone payments totaling $16.5 million, and royalty payments in the low single digits of net sales by the Company of licensed products. Abmuno License Agreement In December 2016, the Company entered into a license agreement (the Abmuno Agreement) with Abmuno Therapeutics LLC (Abmuno) in which it obtained a worldwide exclusive license to develop, use, manufacture, and commercialize products that include an anti-TIGIT antibody. During the years ended December 31, 2020 and 2018, the Company made milestone payments of $3.0 million and $2.8 million, respectively. No expense was incurred during the year ended December 31, 2019. Milestone payments were recorded as research and development expense, as the products have not reached technological feasibility and do not have alternative future use. The Abmuno Agreement also provides for additional clinical, regulatory and commercialization milestone remaining payments of up to $98.0 million as of December 31, 2020. Genentech Collaboration Agreement In December 2019, the Company and Genentech, through F. Hoffmann-La Roche Ltd (collectively, Genentech) entered into a Master Clinical Collaboration Agreement (the Genentech Agreement) pursuant to which the parties may conduct combination clinical studies involving Genentech’s monoclonal antibody, atezolizumab and the Company’s investigational products. Pursuant to the Genentech Agreement, the parties entered into Trial Supplements for the evaluation of etrumadenant and atezolizumab utilizing the MORPHEUS platform in two separate study indications: second and third line metastatic colorectal cancer and first line metastatic pancreatic cancer. The Company and Genentech will each supply their respective investigational products for use in the collaboration studies and will share a portion of the development costs under specific terms as set forth in the agreement. For the years ended December 31, 2020 and 2019, the Company incurred $0.5 million and no expense, respectively, under the collaboration. Strata Collaboration Agreement On April 30, 2019, the Company and Strata Oncology, Inc. (Strata) entered into a Co-Development and Collaboration Agreement (the Co-Development and Collaboration Agreement) to pursue a clinical development collaboration utilizing Strata’s precision drug development platform and proprietary biomarkers to evaluate zimberelimab, the Company’s clinical-stage anti-PD-1 antibody, in patients in a tumor-agnostic fashion. Under the terms of the Co-Development and Collaboration Agreement, the parties will share a portion of development costs for the clinical collaboration under specified terms. Strata is eligible to receive $2.5 million upon the achievement of a development milestone, as well as regulatory and commercial milestones of up to $125.0 million and up to double-digit royalties on U.S. net sales of zimberelimab in the biomarker-identified indication. For the years ended December 31, 2020 and 2019, th e Company made milestone payment s to Strata of zero and $ 2.5 million , respectively, which w as recorded as a research and development expense. For the year ended December 31, 2020, the Company incurred expenses of $ 1.7 million, of which $ 0.3 million had been reimbursed by Strata as development cost sharing. For the year ended December 31, 2019, the Company incurred expenses of $ 1.0 million , of which $ 0.2 million had been reimbursed by Strata as development cost sharing. Net expenses related to this co-development agreement were recorded within research and development expenses. As further consideration in connection with the Co-Development and Collaboration Agreement, the Company issued to Strata 1,257,651 restricted shares of its common stock with an initial measured fair value of $ 15.0 million, which are subject to vesting based upon the achievement of specified regulatory milestones within certain timelines. Expense relating to the restricted shares subject to these milestones is recognized if it is considered probable that the associated shares will vest. The probability of achievement is assessed at the end of each quarterly period. As of December 31, 20 20 , the Company determined that none of the restricted shares were probable of vesting and, as a result, no compensation expense related to the restricted shares has been recognized to date . AstraZeneca Agreement On October 29, 2020 the Company announced a collaboration with AstraZeneca to evaluate domvanalimab, the Company’s investigational anti-TIGIT antibody, in combination with AstraZeneca’s Imfinzi (durvalumab) in a registrational Phase 3 clinical trial in patients with unresectable Stage III non-small cell lung cancer (NSCLC). Under the terms of the agreement, each company will retain existing rights to their respective molecules and any future commercial economics. AstraZeneca will conduct the trial, and each company will supply its respective anti-cancer agent to support the trial. Under the terms of the agreement and subject to the parties’ approval of a final budget for the clinical trial, the Company may be obligated to reimburse AstraZeneca for a portion of the costs incurred. Consistent with the terms of the recently completed Arcus-Gilead partnership, Gilead maintains an option to co-develop and co-commercialize domvanalimab. If Gilead exercises its option to domvanalimab, the trial from this AstraZeneca collaboration is expected to form part of the Arcus and Gilead joint development program and Arcus’s portion of the trial costs would be shared with Gilead.

Convertible Preferred Stock and

Convertible Preferred Stock and Stockholders' Equity (Deficit)	12 Months Ended
	Dec. 31, 2020
Stockholders Equity Note [Abstract]
Convertible Preferred Stock and Stockholders' Equity (Deficit)	Note 8: Convertible Preferred Stock and Stockholders’ Equity (Deficit) The Company’s Certificate of Incorporation, as amended and restated, authorizes the Company to issue 410,000,000 shares of capital stock consisting of 400,000,000 shares common stock and 10,000,000 shares of preferred stock, both par value of $0.0001. In June 2020, pursuant to a shelf registration statement on Form S-3 that was filed in May 2020, the Company issued 12,650,000 shares of its common stock at $27.50 per share in an underwritten public offering (the May 2020 Public Offering). The total number of shares sold consisted of 11,000,000 base shares and an additional 1,650,000 shares sold pursuant to the underwriters’ option exercise. Net proceeds from the May 2020 Public Offering were approximately $326.2 million after deducting underwriting discounts, commissions and other offering expenses. In July 2020, the Company closed the Gilead Collaboration Agreement, Common Stock Purchase Agreement, and the Investor Rights Agreement, each signed with Gilead in May 2020. The transaction closed on July 13, 2020 following expiration of the antitrust waiting period. Upon closing, Gilead made an equity investment of approximately $200 million in the Company by purchasing 5,963,029 shares of Arcus common stock at a per share price of $33.54 pursuant to the Stock Purchase Agreement. Of the $200 million equity investment, approximately $90.6 million was determined to be a premium on the purchase of common stock and allocated to the performance obligations created by the Gilead Collaboration Agreement. See Note 7 and Note 13 for further discussion of the agreements with Gilead. Net proceeds from Gilead’s equity investment were approximately $107.5 million after allocating the premium and deducting direct offering expenses of $1.9 million. As of December 31, 2020 and 2019, the Company had no outstanding convertible preferred stock.

Stock Plans and Stock-Based Com

Stock Plans and Stock-Based Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Plans and Stock-Based Compensation	Note 9: Stock Plans and Stock-Based Compensation Stock Plans The Company grants awards to employees and nonemployees under a series of equity incentive plans, (collectively, the Stock Plans). In May 2015, the Company adopted the 2015 Stock Plan, which was amended and restated in November 2015 (as amended from time to time, the 2015 Plan). The terms of the 2015 Plan permitted option holders to exercise stock options before they vest, subject to certain limitations. Such unvested shares are subject to repurchase by the Company at the original exercise price in the event the option holder’s service to the Company is terminated either voluntarily or involuntarily. As a result of early exercises under the 2015 Plan, approximately 165,133 and 455,158 shares had not vested and were subject to repurchase as of December 31, 2020 and 2019, respectively. The Company treats cash received from the exercise of unvested options as a refundable deposit and classifies such amounts as a liability in its consolidated balance sheets. As of December 31, 2020 and 2019, the Company included cash received for the early exercise of unvested options of $0.7 million and $1.7 million, respectively, allocated to other current and long-term liabilities based on the timing of their expected vesting. Amounts included in liabilities are transferred into common stock and additional paid-in capital as the shares vest, which is generally over a period of 48 months. In March 2018, the Company adopted the 2018 Equity Incentive Plan (2018 Plan), which replaced the 2015 Plan upon completion of the IPO. 3,570,000 shares were reserved under the 2018 Plan plus 709,558 shares remaining available for issuance under the Company’s 2015 Plan and outstanding awards under its 2015 Plan that subsequently expire, lapse unexercised or are forfeited to or repurchased by the Company. In addition, the number of shares reserved for issuance under our 2018 Plan will automatically increase on January 1 of each year beginning January 1, 2019 by a number equal to the smallest of (i) 3,570,000 shares, (ii) 4% of the shares of common stock outstanding on the last business day of the prior fiscal year or (iii) the number of shares determined by our board of directors. As of December 31, 2020, there were 1,106,209 shares available for grant under the 2018 plan. In accordance with the provisions of the 2018 Plan, the number of shares available for issuance under the Plan automatically increased by 2,604,587 shares on January 1, 2021. In January 2020, the Company’s Board of Directors adopted the 2020 Inducement Plan (2020 Plan), pursuant to which it reserved and authorized 3,000,000 shares of the Company’s common stock in order to award non-statutory stock options and other equity-based awards as a material inducement to eligible individuals to enter into employment with the Company. In November 2020, the Company’s Board of Directors authorized an increase of 1,000,000 shares reserved for issuance under the 2020 Plan. As of December 31, 2020 there were 784,975 shares available for grant under the 2020 Plan. The following table, which includes options granted under the Company’s Stock Plans, summarizes option activity: Shares Subject to Outstanding Options Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2019 4,738,004 $ 9.00 Options granted 5,784,550 $ 17.36 Options exercised (392,523 ) $ 8.54 Options forfeited or canceled (237,334 ) $ 10.38 Outstanding at December 31, 2020 9,892,697 $ 13.88 8.81 $ 122,232 Options vested and expected to vest as of December 31, 2020 9,892,697 $ 13.88 8.81 $ 122,232 Options exercisable as of December 31, 2020 2,793,050 $ 10.28 8.12 $ 44,012 During the years ended December 31, 2020, 2019 and 2018, the intrinsic value of shares exercised was $6.8 million, $0.2 million and $0.6 million, respectively, and the fair value of shares vested during the same period was $16.8 million, $7.8 million and $3.0 million, respectively. Restricted Stock Units and Restricted Stock Awards In 2015, in conjunction with the incorporation of the Company, the Company issued a total of 2,777,776 shares of common stock at $0.0004 per share to its two founders, the Chief Executive Officer and the President, under restricted stock agreements. At the date of grant, the shares had an estimated fair value of $0.0004 per share. Under the terms of the restricted stock agreements, shares vested monthly over four years. There were no shares granted under restricted stock agreements during the years ended December 31, 2020, 2019, and 2018. The total grant date fair value of shares vested during the same periods was immaterial. All shares were vested as of December 31, 2020. The Company granted restricted stock units (RSUs) to its employees and directors under the 2018 Plan. The shares subject to the RSUs vest annually or quarterly over four years for employees and annually for directors. Total Restricted Stock Units Weighted Average Grant Date Fair Value Nonvested at December 31, 2019 - $ - RSUs granted 758,950 27.77 RSUs vested (6,250 ) 17.00 RSUs forfeited or canceled (14,050 ) 29.05 Nonvested at December 31, 2020 738,650 $ 27.84 During the year ended December 31, 2020, the total grant date fair value of shares granted under RSUs was $21.1 million . Employee Stock Purchase Plan In March 2018, the Company adopted the 2018 Employee Stock Purchase Plan (2018 ESPP). The 2018 ESPP provides eligible employees with the opportunity to purchase shares of common stock through payroll deductions at a price equal to 85% of the lower of the fair market value per share on the first trading day of the applicable 24-month offering period or the fair market value per share on the applicable purchase date, provided that no more than 3,000 shares of common stock may be purchased by an employee on any purchase date. Also, the value of the shares purchased in any calendar year may not exceed $25,000. The 2018 ESPP is intended to constitute an “employee stock purchase plan” under Section 423(b) of the Internal Revenue Code of 1986, as amended. The 2018 ESPP may be terminated by the Company’s board of directors at any time. A total of 714,000 shares of common stock were initially reserved for issuance under the 2018 ESPP, and the number of shares reserved for issuance under the 2018 ESPP will automatically increase on January 1 of each year beginning on January 1, 2019 by a number of shares equal to the least of (i) 1% of our outstanding shares of common stock on the last day of the prior fiscal year, (ii) 1,071,000 shares or (iii) a number of shares determined by our board of directors. As of December 31, 2020, there were 1,190,422 shares available for purchase under the 2018 ESPP. In accordance with the provisions of the 2018 ESPP, the number of shares available for purchase under the Plan automatically increased by 651,146 shares on January 1, 2021. Non-employee stock-based compensation As of December 31, 2020, 2019 and 2018, 31,986, 372,774 and 14,918 respectively, of vested stock options and 21,165, 308,596, and 31,388, respectively, of unvested stock options were held by non-employees. The amount of stock-based compensation expense related to non-employees recognized in the consolidated financial statements for the years ended December 31, 2020, 2019 and 2018 was $0.7 million, $0.9 million and $0.3 million, respectively. Stock-based compensation expense The following table summarizes employee and non-employee stock-based compensation expense for the years ended December 31, 2020, 2019 and 2018, and also the allocation within the consolidated statements of operations and comprehensive loss (in thousands): Year Ended December 31, 2020 2019 2018 Research and development $ 11,195 $ 4,152 $ 2,255 General and administrative 10,630 4,829 1,619 Total stock-based compensation $ 21,825 $ 8,981 $ 3,874 As of December 31, 2020, unrecognized employee and nonemployee compensation costs related to non-vested stock option awards and RSUs totaled $88.9 million, and is expected to be recognized over a weighted average period of 2.9 years Valuation Assumptions Prior to the Company’s IPO, the fair value of the shares of common stock underlying stock-based awards was determined by the board of directors, with input from management. Because there was no public market for the Company’s common stock, the board of directors determined the fair value of the common stock on the grant-date of the stock-based award by considering a number of objective and subjective factors, including enterprise valuations of the Company’s common stock performed by an unrelated third-party specialist, valuations of comparable companies, sales of the Company’s convertible preferred stock to unrelated third parties, operating and financial performance, the lack of liquidity of the Company’s capital stock, and general and industry-specific economic outlook. The board of directors intended all options granted to be exercisable at a price per share not less than the estimated per share fair value of common stock underlying those options on the date of grant. Following the Company’s IPO, the market traded price of the shares of common stock underlying the stock-based awards is the fair value of our stock as reported on the New York Stock Exchange on the grant date. Company estimates the fair value of options and ESPP shares utilizing the Black-Scholes option pricing model, which is dependent upon several variables, such as expected term, volatility, risk-free interest rate, and expected dividends. Each of these inputs is subjective and generally requires significant judgment to determine. The following assumptions were used to calculate the fair value of stock-based compensation for the years ended December 31, 2020, 2019, and 2018: Stock Options Year Ended December 31, 2020 2019 2018 Risk-free interest rate 0.4% - 0.5% 1.6% - 2.3% 1.2% - 3.1% Expected term (in years) 6.02 6.02 5.16-9.95 Volatility 76.5% - 78.5% 71.8% - 74.6% 58.7%-75.5% Dividend yield 0% 0% 0% ESPP Year Ended December 31, 2020 2019 2018 Risk-free interest rate 0.1% - 0.2% 1.6% - 2.3% 2.1% - 2.6% Expected term (in years) 0.5-2.0 0.5-2.0 0.5-2.0 Volatility 66.6% - 136.0% 64.8% - 77.1% 54.3% - 65.5% Dividend yield 0% 0% 0% Expected Term — The Company has opted to use the “simplified method” for estimating the expected term of options, whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option (generally 10 years). Expected Volatility — Due to the Company’s limited operating history and a lack of company specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The historical volatility data was computed using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. Risk-Free Interest Rate — The risk-free rate assumption is based on the U.S. treasury yield in effect at the time of grant for instruments with maturities similar to the expected term of the Company’s stock options. Expected Dividend — The Company has not issued any dividends in its history and does not expect to issue dividends over the life of the options and therefore has estimated the dividend yield to be zero.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Loss per Share	Note 10. Net Loss per Share The following table sets forth the computation of basic and diluted net loss per share (in thousands, except share and per share data): Year Ended December 31, 2020 2019 2018 Numerator: Net loss $ (122,858 ) $ (84,710 ) $ (49,594 ) Denominator: Weighted-average common shares outstanding 56,354,059 45,385,489 36,357,336 Less: weighted-average common shares subject to repurchase (1,566,941 ) (1,559,498 ) (1,739,099 ) Weighted-average common shares used to compute basic and diluted net loss per share 54,787,118 43,825,991 34,618,237 Net loss per share, basic and diluted $ (2.24 ) $ (1.93 ) $ (1.43 ) The following outstanding potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive: At December 31, 2020 2019 2018 Common stock options issued and outstanding 9,892,697 4,738,004 1,458,079 Unvested restricted stock issued as part of collaboration agreement 1,257,651 1,257,651 - Unvested early exercised common stock options 165,133 455,158 927,123 Unvested restricted stock units 738,650 - - Employee Stock Purchase Plan shares 18,219 - - Unvested restricted common stock - - 289,352 Total 12,072,350 6,450,813 2,674,554

Provision for Income Taxes

Provision for Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Provision for Income Taxes	Note 11: Provision for Income Taxes The provision for income taxes differs from the amount expected by applying the federal statutory rate to the loss before taxes as follows: Year Ended December 31, 2020 2019 2018 Federal statutory income tax rate 21.00 % 21.00 % 21.00 % Equity investment 4.15 % 0.00 % 0.00 % Research and development credits 3.10 % 0.00 % 0.00 % Change in valuation allowance (27.35 )% (19.65 )% (19.46 )% Non-deductible expenses and other (0.90 )% (1.35 )% (1.54 )% Total 0.00 % 0.00 % 0.00 % As of December 31, 2020 and 2019, the components of the Company’s deferred tax assets are as follows (in thousands): Year Ended December 31, 2020 2019 Deferred tax assets: Federal and state net operating loss carryforwards $ 54,526 $ 30,049 Research and development credits carryforwards 11,209 8,077 Depreciation 9,068 6,052 Deferred Revenue 2,407 3,277 Lease liability 3,831 - Other 5,890 2,965 Total deferred tax assets 86,931 50,420 Deferred tax liabilities: Right-of-use assets (2,704 ) - Total deferred tax liabilities (2,704 ) - Less valuation allowance (84,227 ) (50,420 ) Net deferred tax assets $ - $ - Deferred income taxes reflect the net tax effects of (a) temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes, and (b) operating losses and tax credit carryforwards. The Company’s accounting for deferred taxes involves the evaluation of a number of factors concerning the realizability of its net deferred tax assets. The Company considered factors such as its history of operating losses, the nature of the Company’s deferred tax assets, and the timing, likelihood and amount, if any, of future taxable income during the periods in which those temporary differences and carryforwards become deductible, including amounts that may arise under the collaboration agreement with Gilead entered into in 2020. As a result of the Company's evaluation of these factors, including the uncertainty that exists with respect to the option fees and milestone payments, the Company does not believe that it is more likely than not that the deferred tax assets will be realized. Accordingly, a full valuation allowance has been established and no deferred tax asset is shown in the accompanying consolidated balance sheets. The valuation allowance increased by approximately $33.8 million, $19.7 million and $12.2 million, respectively, for the years ended December 31, 2020, 2019 and 2018. At December 31, 2020, the Company has total net operating loss carryforwards (NOLs) of $253.3 million for federal income tax purposes, of which approximately $47.4 million begin to expire in 2035 and approximately $205.9 million that have no expiration date and federal research tax credits of approximately $9.9 million that begin to expire in 2035. The Company also has state NOLs of approximately $15.9 million that begin to expire in 2035, and state research tax credits of approximately $5.1 million that have no expiration date. Use of the NOLs and credit carryforwards may be subject to a substantial annual limitation due to the ownership change provisions of U.S. tax law, as defined in Section 382 and 383 of the Internal Revenue Code of 1986, as amended, and similar state provisions. The annual limitation may result in the expiration of NOLs and credits before use. The Company determined that an ownership change , as defined under IRC Section 382, occurred in the current and previous years. While the Company does not expect these ownership changes to result in the expiration of net operating loss and credit carryforwards prior to utilization, the Company is subject to an annual limitation on the use of its tax attributes. The limitation on the Company's use of net operating loss and credit carryforwards could reduce the Company's ability to use a portion of the tax attributes to offset future taxable income. The Company has not been audited by the Internal Revenue Service, any state or foreign tax authority. The Company is subject to taxation in the United States and also beginning in 2017, in Australia. Because of the net operating loss and research credit carryforwards, all of the Company’s tax years, from 2015 to 2019, remain open to U.S. federal and California state tax examinations. In addition, the Company’s tax years from 2017 to 2019 are open to examination in Australia. There were no interest or penalties accrued at December 31, 2020, 2019 or 2018. Uncertain Tax Positions The Company follows the provisions of FASB Accounting Standards Codification (ASC 740-10), Accounting for Uncertainty in Income Taxes Due to the full valuation allowance at December 31, 2020 and 2019, current adjustments to the unrecognized tax benefit will have no impact on the Company’s effective income tax rate; any adjustments made after the valuation allowance is released will have an impact on the tax rate. The following table summarizes the activity related to our unrecognized tax benefits (in thousands): Year Ended December 31, 2020 2019 2018 Beginning balance $ 2,165 $ 1,084 $ 622 Additions (decreases) for tax positions taken in a prior year (258 ) (7 ) 8 Additions for tax positions taken in current year 1,246 1,088 454 Ending balance $ 3,153 $ 2,165 $ 1,084 The Company does not anticipate material changes to its uncertain tax positions through the next 12 months.

Commitments

Commitments	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments	Note 12: Commitments Purchase Commitments The Company has contractual arrangements with research and development organizations and suppliers; however, these contracts are generally cancelable on 30 days’ notice and the obligations under these contracts are largely based on services performed. Indemnification As permitted under Delaware law and in accordance with the Company’s bylaws, the Company is required to indemnify its officers and directors for certain events or occurrences while the officer or director is or was serving in such capacity. The Company is also party to indemnification agreements with its directors and officers. The Company believes the fair value of the indemnification rights and agreements is minimal. Accordingly, the Company has not recorded any liabilities for these indemnification rights and agreements as of December 31, 2020 and 2019.

Related Parties

Related Parties	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Parties	Note 13. Related parties Relationship and transactions with Gilead Sciences, Inc. (Gilead) As of December 31, 2020, Gilead held approximately 13% of the Company’s outstanding common stock. These holdings resulted from Gilead’s investment in the Company of approximately $56.7 million, net of offering costs, by purchasing 2,200,000 shares of common stock at a per share price of $27.50 in the May 2020 Public Offering as well as Gilead’s acquisition of 5,963,029 shares under the Stock Purchase Agreement. Gilead has the right, at its option, to purchase up to a maximum of 35% of the Company’s then-outstanding voting common stock, from time to time over the next five years. Gilead also has the right under the Investor Rights Agreement to designate two individuals to be appointed to the Company’s board of directors. The Company appointed the first Gilead designee, Merdad Parsey, M.D., Ph.D. and Michael Quigley, Ph.D., to its board of directors pursuant to the Investor Rights Agreement. See Note 7 for further discussion of the agreements with Gilead. At December 31, 2020, the Company had a $0.9 million cost sharing receivable recorded on the consolidated balance sheets under receivable from collaboration partners, to be invoiced the following quarter. The Company also had $185.4 million in deferred revenue at December 31, 2020, of which $117.8 million represented the long-term portion of deferred revenue allocated to performance obligations not expected to be completed within one year of the balance sheet date, which was recorded in deferred revenue, noncurrent on the consolidated balance sheets. The Company also recognized $9.7 million in contract liabilities for future development and commercialization services which Gilead prepaid For the year ended December 31, 2020, the Company recognized $70.5 million in revenue under the Gilead Collaboration Agreement. The Company also recognized a $3.4 million reduction in research and development expense related to its cost-sharing provisions of the agreement. The Company received $175 million in upfront payments from Gilead in connection with the Option, License and Collaboration Agreement and identified $100 million in unconstrained consideration to be received in 2022. In addition, the Company received $200 million from Gilead in connection with the Stock Purchase Agreement, of which approximately $109.4 million represented the fair value of stock purchased at the transaction closing date in July 2020 with the remaining premium of $90.6 million allocated to the transaction price.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plan	Note 14: Employee Benefit Plan The Company sponsors a 401(k) defined contribution plan for its employees. This plan provides for tax-deferred salary deductions for all employees. Employee contributions are voluntary. Employees may contribute up to 100% of their annual compensation to this plan, as limited by an annual maximum amount as determined by the Internal Revenue Service. The Company may match employee contributions in amounts to be determined at the Company’s sole discretion. The Company made no contributions to the plan for the years ended December 31, 2020, 2019 and 2018.

Selected Unaudited Quarterly Fi

Selected Unaudited Quarterly Financial Data	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Unaudited Quarterly Financial Data	Note 15: Selected Unaudited Quarterly Financial Data The following table summarizes the Company’s unaudited quarterly financial data for the last two years (in thousands, except share and per share data): First Quarter Second Quarter Third Quarter Fourth Quarter 2020 Total revenues $ 1,750 $ 1,750 $ 64,530 $ 9,487 Total operating expenses $ 30,150 $ 47,125 $ 62,978 $ 61,499 Net income (loss) $ (27,753 ) $ (45,074 ) $ 1,822 $ (51,853 ) Net income (loss) per share — basic $ (0.63 ) $ (0.93 ) $ 0.03 $ (0.82 ) Net income (loss) per share — diluted $ (0.63 ) $ (0.93 ) $ 0.03 $ (0.82 ) Weighted average number of shares, basic 44,282,607 48,556,843 62,599,193 63,527,932 Weighted average number of shares, diluted 44,282,607 48,556,843 65,145,707 63,527,932 2019 Total revenues $ 1,750 $ 1,750 $ 1,750 $ 9,750 Total operating expenses $ 20,523 $ 30,910 $ 24,999 $ 27,277 Net loss $ (17,670 ) $ (28,090 ) $ (22,352 ) $ (16,598 ) Net loss per share — basic and diluted $ (0.41 ) $ (0.64 ) $ (0.51 ) $ (0.38 ) Weighted average number of shares, basic and diluted 43,508,592 43,797,718 43,939,281 44,056,407

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Event	Note 16: Subsequent Event In February 2021, Gilead increased its ownership in the Company by purchasing 5,650,000 additional shares of the Company’s common stock at a purchase price of $39.00 per share for total proceeds to the Company of $220.4 million. After the transaction, Gilead owned approximately $19.5% of the Company’s outstanding shares of common stock.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements and accompanying notes have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP) and include all adjustments necessary for the fair presentation of the Company’s financial position for the periods presented.
Principles of Consolidation	Principles of Consolidation The accompanying consolidated financial statements are comprised of Arcus Biosciences, Inc. and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses, as well as related disclosure of contingent assets and liabilities. Estimates were used to determine the standalone selling price of performance obligations and the timing of revenue recognition, the value of stock-based awards and other issuances, accruals for research and development costs, useful lives of long-lived assets, and uncertain tax positions. Actual results could differ materially from the Company’s estimates.
Risks and Uncertainties	Risk and Uncertainties The Company’s future results of operations involve a number of risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of clinical trial results and achievement of milestones, uncertainty of regulatory approval of the Company’s potential drug candidates, uncertainty of market acceptance of the Company’s product candidates, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals and sole source suppliers. The Company’s investigational products require approval from the U.S. Food and Drug Administration (FDA) and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any investigational products will receive the necessary approvals. If the Company does not obtain regulatory approval and does not successfully commercialize any of its investigational products, it would have a materially adverse impact on the Company.
Segments	Segments The Company operates and manages its business as one reportable and operating segment, which is the business of developing and commercializing cancer therapies. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating and evaluating financial performance. All long-lived assets are maintained in the United States of America.
Cash Equivalents and Investments	Cash Equivalents and Investments Cash equivalents consist of marketable securities having an original maturity of three months or less at the time of purchase. Short-term investments have maturities of greater than three months and less than twelve months at the time of purchase. Long-term investments have maturities greater than 12 months at the time of purchase. Collectively, cash equivalents, short-term and long-term investments are considered available-for-sale and are recorded at fair value. Unrealized gains and losses are recorded in accumulated other comprehensive loss. Realized gains and losses are included in interest and other income, net in the consolidated statements of operations and comprehensive loss. The basis on which the cost of a security sold or amount reclassified out of accumulated other comprehensive income into earnings is determined using the specific identification method.
Reconciliation of Cash, Cash Equivalents, and Restricted Cash as Reported in Consolidated Statements of Cash Flows	Reconciliation of Cash, Cash Equivalents, and Restricted Cash as Reported in Consolidated Statements of Cash Flows Restricted cash at December 31, 2020 and 2019 represents cash balances held as security in connection with the Company’s facility lease agreements. The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the consolidated balance sheets to the total shown in the consolidated statements of cash flows (in thousands): December 31, 2020 December 31, 2019 Cash and cash equivalents $ 173,415 $ 57,937 Restricted cash 203 203 Cash, cash equivalents and restricted cash $ 173,618 $ 58,140
Fair Value Measurements	Fair Value Measurements Fair value accounting is applied for all financial assets and liabilities, including short-term and long-term investments, and non-financial assets and liabilities that are recognized or disclosed at fair value in the consolidated financial statements on a recurring basis (at least annually). The carrying amount of the Company’s financial instruments, including receivable from a related party, accounts payable and accrued expenses and other current liabilities approximate fair value due to their short-term maturities.
Concentration of Credit Risk	Concentration of Credit Risk Cash equivalents, short-term and long-term investments are financial instruments that potentially subject the Company to concentrations of credit risk. The Company invests in money market funds, treasury bills and notes, government bonds, commercial paper and corporate notes. The Company limits its credit risk associated with cash equivalents, short-term and long-term investments by placing them with banks and institutions it believes are highly credit worthy and in highly rated investments.
Property and Equipment	Property and Equipment Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from one to five years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. Upon retirement or sale, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statement of operations and comprehensive loss.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment charge would be recorded when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. Impairment, if any, is assessed using discounted cash flows or other appropriate measures of fair value. The Company did not recognize any impairment charges for the years ended December 31, 2020, 2019 and 2018.
Collaborative Arrangements and Contracts with Customers	Collaborative Arrangements and Contracts with Customers The Company assesses whether its collaboration agreements are subject to Accounting Standards Codification (ASC) Topic 808, Collaborative Arrangements and whether both parties have active participation in the arrangement and are exposed to significant risks and rewards. To the extent that the arrangement falls within the scope of ASC 808, the Company applies the unit of account guidance under ASC Topic 606, Revenue from Contracts with Customers (ASC 606) , to identify distinct performance obligations, and then determine whether a customer relationship exists for each distinct performance obligation. If the Company determines a performance obligation within the arrangement is with a customer, it applies the guidance in ASC 606. If a portion of a distinct bundle of goods or services within an arrangement is not with a customer, then the unit of account is not within the scope of ASC 606, and the recognition and measurement of that unit of account shall be based on analogy to authoritative accounting literature or, if there is no appropriate analogy, a reasonable, rational, and consistently applied accounting policy election. The Company recognizes revenue when its customer obtains control of promised goods or services in a contract for an amount that reflects the consideration the Company expects to receive in exchange for those goods or services. For contracts with customers, the Company performs The estimation of the stand-alone selling price may include such estimates as forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if they can be satisfied at a point in time or over time, and the Company measures the services delivered to the customer, which are periodically reviewed based on the progress of the related program. The effect of any change made to an estimated input component and, therefore revenue or expense recognized, would be recorded as a change in estimate. In addition, variable consideration (e.g. milestone payments) must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. The Company enters into collaborative arrangements that typically include one of more of the following: (i) license fees; (ii) milestone payments related to the achievement of developmental, regulatory, or commercial goals; (iii) royalties on net sales of licensed products; (iv) fees attributable to options to intellectual property; and (v) cost-sharing or research and development (R&D) funding arrangements. When a portion of non‑refundable upfront fees or other payments received are allocated to continuing performance obligations under the terms of a collaborative arrangement, they are recorded as deferred revenue and recognized as revenue when (or as) the underlying performance obligation is satisfied. Fees attributable to options are deferred until the option expires or is exercised. The Company classifies contract liabilities as current when it expects to satisfy its performance obligations within one year, and noncurrent when the Company expects to satisfy those performance obligations in greater than one year. When an option is exercised, the performance obligations associated with the option are identified, which will determine the accounting for the transaction price attributable to the option. As part of the accounting for these arrangements, the Company must develop estimates and assumptions that require judgment to determine the underlying stand-alone selling price for each performance obligation which determines how the transaction price is allocated among the performance obligation. To determine the stand-alone selling price, the Company may consider items such as forecasted revenues, development timelines, discount rates, and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if it can be satisfied at a point in time or over time. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. License Fees If a license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, upfront fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments and Variable Consideration At the inception of each arrangement that includes milestone payments or variable consideration, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated value is included in the transaction price. Milestone payments that are not within the control of the Company or the Company’s collaboration partner, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration or other revenues and earnings in the period of adjustment. Cost-Sharing or R&D Funding Arrangements Under certain collaborative arrangements, the Company has been reimbursed for a portion of its research and development expenses, including costs of drug supplies. When these R&D services are performed under a reimbursement or cost sharing model with a collaboration partner, the Company records these reimbursements as a reduction of R&D expense in its consolidated statements of operations. Royalties For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its collaborative arrangements.
Research and Development Expenses	Research and Development Expenses Research and development costs are expensed as incurred. Research and development expenses consist primarily of personnel costs for the Company’s research and development employees, costs incurred to third-party service providers for the conduct of research, preclinical and clinical studies, laboratory supplies and equipment maintenance costs, consulting and other related expenses. Also included are payments under collaborative arrangements, including up-front and milestone payments, license and option fees and expense reimbursements to the collaboration partners, as well as non-personnel costs such as professional fees payable to third parties for preclinical and clinical studies and research services, laboratory supplies and equipment maintenance, product licenses, and other consulting costs. The Company estimates research, preclinical and clinical service organizations, based on services performed, pursuant to contracts with third-party research and development organizations that conduct and manage research, preclinical and clinical activities on its behalf. Most of the Company’s clinical studies are performed by third-party contract research organizations (CROs), and as a result clinical study costs are a significant component of research and development expenses. The Company estimates these expenses based on discussions with internal management personnel and external service providers as to the progress or stage of completion of services and the contracted fees to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. Payments associated with licensing agreements to acquire licenses to develop, use, manufacture and commercialize products that have not reached technological feasibility and do not have alternative future use are expensed as incurred. Payments made to third parties under these arrangements in advance of the performance of the related services by the third parties are recorded as prepaid expenses until the services are rendered.
Leases and Rent Expense	Leases and Rent Expense The Company leases laboratory and office space in an office park in Hayward, California under a non-cancelable operating lease with terms that expire from 2025 to 2029, subject to options for the Company to extend the lease term. The Company also leases space in Brisbane, California under a non-cancelable operating lease that is expected to commence in 2021 and extend through 2031. Prior to January 1, 2020, the Company recognized related rent expense on a straight-line basis over the term of the lease. Incentives granted under the Company’s facilities lease, including allowances for leasehold improvements and rent holidays, were recognized as reductions to rental expense on a straight-line basis over the term of the lease. Deferred rent consisted of the difference between cash payments and the rent expense recognized. Subsequent to the adoption of the new leasing standard on January 1, 2020, the Company recognizes a lease asset for its right to use the underlying asset and a lease liability for the corresponding lease obligation. The Company determines whether an arrangement is or contains a lease at contract inception. Operating leases are included in operating lease right-of-use assets, other accrued liabilities, and operating lease liabilities, noncurrent in our consolidated balance sheet at December 31, 2020. Operating lease right-of-use assets and liabilities are recognized at the lease commencement date based on the present value of lease payments over the lease term. In determining the net present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the lease commencement date. The incremental borrowing rate represents the interest rate the Company would incur at lease commencement to borrow an amount equal to the lease payments on a collateralized basis over the term of a lease. The Company considers a lease term to be the noncancelable period that it has the right to use the underlying asset, including any periods where it is reasonably assured the Company will exercise the option to extend the contract. Periods covered by an option to extend are included in the lease term if the lessor controls the exercise of that option. The Company elected to not apply the recognition requirements of the new leasing standard to short-term leases with terms of 12 months or less which do not include an option to purchase the underlying asset that the Company is reasonably certain to exercise. For short-term leases, lease payments are recognized as operating expenses on a straight-line basis over the lease term.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation arrangements in accordance with ASC 718, Stock Compensation Equity Based Payments to Non-Employees No. 2018-07 (Topic 718), Compensation – Stock Compensation, Stock-based awards granted include stock options and restricted stock units (RSUs). Accounting standards require the recognition of compensation expense, using a fair value-based method, for costs related to all stock-based payments. The Company’s determination of the fair value of stock options with time-based vesting on the date of grant utilizes the Black-Scholes option-pricing model, and is impacted by the Company’s common stock price as well as other variables including, but not limited to, expected term that options will remain outstanding, expected common stock price volatility over the term of the option awards, risk-free interest rates and expected dividends. Compensation expense associated with restricted stock units is based on the fair value of common stock on the date of the grant. The fair value of a stock-based award is recognized over the period during which an optionee is required to provide services in exchange for the option award, known as the requisite service period (usually the vesting period) on a straight-line basis. Stock-based compensation expense is recognized based on the fair value determined on the date of grant and is reduced for forfeitures as they occur. Estimating the fair value of equity-settled awards as of the grant date using valuation models, such as the Black-Scholes option pricing model, is affected by assumptions regarding a number of complex variables. Changes in the assumptions can materially affect the fair value and ultimately how much stock-based compensation expense is recognized. These inputs are subjective and generally require significant analysis and judgment to develop.
Income Taxes	Income Taxes The Company provides for income taxes under the asset and liability method. Current income tax expense or benefit represents the amount of income taxes expected to be payable or refundable for the current year. Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and tax bases of assets and liabilities and net operating loss and credit carryforwards, and are measured using the enacted tax rates and laws that will be in effect when such items are expected to reverse. Deferred income tax assets are reduced, as necessary, by a valuation allowance when management determines it is more likely than not that some or all of the tax benefits will not be realized. The Company accounts for uncertain tax positions in accordance with ASC 740-10, Accounting for Uncertainty in Income Taxes. The Company includes any penalties and interest expense related to income taxes as a component of other expense and interest income, net, as necessary. On March 18, 2020, the Families First Coronavirus Response act (FFCR Act), and on March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (CARES Act) were each enacted in response to the COVID-19 pandemic. The FFCR Act and the CARES Act contain numerous tax-related provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. On June 29, 2020 California State Assembly Bill 85 (the Trailer Bill) was enacted which suspends the use of California net operating loss (NOL) deductions and limits the use of certain tax credits, including research and development tax credits, for the 2020, 2021, and 2022 tax years. The FFCR Act, CARES Act and Trailer Bill did not have a material impact on the Company’s consolidated financial statements as of December 31, 2020; however, the Company continues to examine the impacts the FFCR Act, CARES Act and Trailer Bill may have on its business, results of operations, financial condition and liquidity.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss and net unrealized income and losses on available-for-sale securities, which are presented in a single continuous statement. Other comprehensive income (loss) is also disclosed in the consolidated balance sheets and statements of stockholders’ equity in accumulated other comprehensive income (loss), and is stated net of related tax effects, if any.
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. The Company excludes the weighted-average shares subject to repurchase from its calculation of weighted average of common shares outstanding. For purposes of the diluted net loss per share calculation, outstanding common stock options are considered to be potentially dilutive securities. Because the Company reported a net loss for the years ended December 31, 2020, 2019 and 2018, and the inclusion of the potentially dilutive securities would be antidilutive, diluted net loss per share is the same as basic net loss per share for all periods.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes In November 2018, the FASB issued ASU No. 2018-18 (Topic 808), Collaborative Arrangements Revenue from Contracts with Customers (Topic 606) In August 2018, the FASB issued ASU No.2018-13 (Topic 820), Fair Value Measurement. In August 2018, the FASB issued ASU No.2018-15 (Subtopic 350-40), Intangibles – Goodwill and Other – Internal-Use Software. In February 2016, the FASB issued ASU No. 2016-02 (Topic 842), Leases No. 2018-10 Codification Improvements to Topic 842, Leases No. 2018-11, Leases (Topic 842): Targeted Improvements The Company adopted this standard on January 1, 2020 using the modified retrospective approach and elected the package of practical expedients permitted under transition guidance, which allowed the Company to carry forward its historical assessments of: 1) whether contracts are or contain leases, 2) lease classification and 3) initial direct costs. The Company did not elect the practical expedient allowing the use-of-hindsight which would require the Company to reassess the lease term of its leases based on all facts and circumstances through the effective date and did not elect the practical expedient pertaining to land easements as this is not applicable to the current contract portfolio. The Company elected the post-transition practical expedient to not separate lease components from nonlease components for all existing lease classes. The Company also elected a policy of not recording leases on its consolidated balance sheets when the leases have a term of 12 months or less and the Company is not reasonably certain to elect an option to purchase the leased asset. The adoption of this standard resulted in the recognition of a right-of-use (ROU) asset of $5.8 million and lease liabilities of $10.1 million, comprised of $1.2 million and $8.9 million of current and noncurrent liabilities, respectively. The adoption also resulted in the derecognition of the deferred rent balance of $4.3 million as of January 1, 2020. The adoption of the standard had no impact on the Company’s consolidated statements of operations and comprehensive loss or to its cash flows from or used in operating, financing, or investing activities on its consolidated statements of cash flows. No cumulative-effect adjustment within accumulated deficit was required to be recorded as a result of adopting this standard. In June 2016, the FASB issued ASU No. 2016 -13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments The Company adopted this standard on January 1, 2020 using the modified retrospective approach. The Company adopted this ASU as of January 1, 2020 with an immaterial impact on its financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the consolidated balance sheets to the total shown in the consolidated statements of cash flows (in thousands): December 31, 2020 December 31, 2019 Cash and cash equivalents $ 173,415 $ 57,937 Restricted cash 203 203 Cash, cash equivalents and restricted cash $ 173,618 $ 58,140

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Schedule of Financial Instruments (Excluding Restricted Cash) Measured at Fair Value on Recurring Basis	The following tables set forth the Company’s financial instruments (excluding restricted cash) that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): December 31, 2020 Total Level 1 Level 2 Level 3 Money market funds $ 146,468 $ 146,468 $ - $ - U.S. treasury securities 301,112 - 301,112 - U.S. government agency obligations 25,001 - 25,001 - Corporate securities and commercial paper 262,505 - 262,505 - Total assets measured at fair value $ 735,086 $ 146,468 $ 588,618 $ - December 31, 2019 Total Level 1 Level 2 Level 3 Money market funds $ 45,498 $ 45,498 $ - $ - U.S. treasury securities 74,854 - 74,854 - Corporate securities and commercial paper 67,918 - 67,918 - Total assets measured at fair value $ 188,270 $ 45,498 $ 142,772 $ -
Schedule of Investments Classified as Available for Sale Securities with Contractual Maturities	Classified as (with contractual maturities): Year Ended December 31, 2020 2019 Cash and cash equivalents $ 173,415 $ 57,937 Short-term investments (due within one year) 555,231 130,333 Long-term investments (due between one and two years) 6,440 - $ 735,086 $ 188,270
Schedule of Fair Value and Amortized Cost of Investments in Marketable Securities by Major Security Type	The fair value and amortized cost of investments in marketable securities by major security type as of December 31, 2020 and 2019 are presented in the tables that follow (in thousands): Amortized Cost Unrealized Gain Unrealized Loss Fair Value As of December 31, 2020: Money market funds $ 146,468 $ - $ - $ 146,468 U.S. treasury securities 301,075 38 (1 ) 301,112 U.S. government agency obligations 24,997 4 - 25,001 Corporate securities and commercial paper 262,502 15 (12 ) 262,505 Total $ 735,042 $ 57 $ (13 ) $ 735,086 Amortized Cost Unrealized Gain Unrealized Loss Fair Value As of December 31, 2019: Money market funds $ 45,498 $ - $ - $ 45,498 U.S. treasury securities 74,801 12 (1 ) 74,812 Corporate securities and commercial paper 67,907 55 (2 ) 67,960 Total $ 188,206 $ 67 $ (3 ) $ 188,270

Consolidated Balance Sheet Co_2

Consolidated Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net consisted of the following (in thousands): As of December 31, 2020 2019 Scientific equipment $ 9,902 $ 8,168 Furniture and equipment 1,521 1,165 Capitalized software 225 146 Leasehold improvements 11,111 10,834 Construction in progress 2,336 238 Total 25,095 20,551 Less: Accumulated depreciation and amortization (14,288 ) (11,221 ) Property and equipment, net $ 10,807 $ 9,330
Summary of Other Accrued Liabilities	Other accrued liabilities consisted of the following (in thousands): As of December 31, 2020 2019 Accrued personnel expenses 8,632 $ 4,571 Professional fees 295 183 Other 616 196 Total other accrued liabilities $ 9,543 $ 4,950

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Schedule of Future Minimum Lease Payments	As of December 31, 2020, the Company’s future minimum lease payments were as follows (in thousands): Year Ended December 31, 2020 (1) 2019 (2) 2020 - 2,105 2021 4,041 2,195 2022 3,409 2,265 2023 3,522 2,339 2024 3,640 2,415 2025 3,340 2,072 Thereafter 4,311 - Total undiscounted future minimum lease payments 22,263 13,391 Less: Imputed interest (4,153 ) N/A Total operating lease liabilities 18,110 N/A Less: Current portion of operating lease liabilities (included in other current liabilities) (2,867 ) N/A Operating lease liabilities, noncurrent 15,243 N/A (1) Presented in accordance with ASC 842. (2) Presented in accordance with ASC 840. N/A items not required under ASC 840.

License and Collaboration Agr_2

License and Collaboration Agreements (Tables)	12 Months Ended
	Dec. 31, 2020
Summary of Revenues by Collaboration and by Category of Revenue	The following table summarizes details of revenues by collaboration and by category of revenue: Year Ended December 31, Revenues recognized: Over time Point in time 2020 2019 2018 Gilead license to zimberelimab * $ 55,096 $ - $ - Gilead access rights related to the Company's research and development pipeline * 15,421 - - Taiho license to zimberelimab * - 8,000 - Taiho license to etrumadenant * - - 3,000 Taiho collaboration agreement * 7,000 7,000 5,353 Total collaboration and license revenue $ 77,517 $ 15,000 $ 8,353
Summary of Revenue Recognized as a Result of Changes in Deferred Revenue	The Company recognized the following revenue as a result of changes in the deferred revenue balance during the period below (in thousands): Year Ended December 31, Revenue recognized in the period from: 2020 2019 2018 Amounts included in deferred revenue at the beginning of the period $ 7,000 $ 7,000 $ 5,353 Performance obligations satisfied in previous period - - -
Schedule of Payments Allocated to Performance Obligations	At the transaction closing date, these payments were allocated to the performance obligations identified as follows: Amount Allocation of transaction price Upfront cash consideration $ 175,000 Payment for access rights related to the Company's research and development pipeline 100,000 Premium from Stock Purchase Agreement 90,600 Total transaction price allocated to revenue $ 365,600 Allocation to performance obligations Zimberelimab license $ 55,096 Etrumadenant option 126,960 Domvanalimab option 36,728 Access rights related to the Company's research and development pipeline 137,113 Development and commercialization services for zimberelimab 9,703 Total $ 365,600
Gilead and Taiho
Summary of Revenues	The following table summarizes the revenues received as a result of the Company’s collaboration agreements with Gilead Sciences, Inc. (Gilead) and Taiho Pharmaceutical Co., Ltd. (Taiho): Year Ended December 31, 2020 2019 2018 License revenue $ 55,096 $ 8,000 $ 3,000 Collaboration revenue 22,421 7,000 5,353 Collaboration and license revenue $ 77,517 $ 15,000 $ 8,353

Stock Plans and Stock-Based C_2

Stock Plans and Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Option Activity Includes Options Granted	The following table, which includes options granted under the Company’s Stock Plans, summarizes option activity: Shares Subject to Outstanding Options Weighted Average Exercise Price Per Share Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2019 4,738,004 $ 9.00 Options granted 5,784,550 $ 17.36 Options exercised (392,523 ) $ 8.54 Options forfeited or canceled (237,334 ) $ 10.38 Outstanding at December 31, 2020 9,892,697 $ 13.88 8.81 $ 122,232 Options vested and expected to vest as of December 31, 2020 9,892,697 $ 13.88 8.81 $ 122,232 Options exercisable as of December 31, 2020 2,793,050 $ 10.28 8.12 $ 44,012
Summary of Restricted Stock Units Activity	The Company granted restricted stock units (RSUs) to its employees and directors under the 2018 Plan. The shares subject to the RSUs vest annually or quarterly over four years for employees and annually for directors. Total Restricted Stock Units Weighted Average Grant Date Fair Value Nonvested at December 31, 2019 - $ - RSUs granted 758,950 27.77 RSUs vested (6,250 ) 17.00 RSUs forfeited or canceled (14,050 ) 29.05 Nonvested at December 31, 2020 738,650 $ 27.84
Summary of Employee and Non-Employee Stock-based Compensation Expense	The following table summarizes employee and non-employee stock-based compensation expense for the years ended December 31, 2020, 2019 and 2018, and also the allocation within the consolidated statements of operations and comprehensive loss (in thousands): Year Ended December 31, 2020 2019 2018 Research and development $ 11,195 $ 4,152 $ 2,255 General and administrative 10,630 4,829 1,619 Total stock-based compensation $ 21,825 $ 8,981 $ 3,874
Schedule of Assumptions Used to Calculate Fair Value of Stock-Based Compensation	The following assumptions were used to calculate the fair value of stock-based compensation for the years ended December 31, 2020, 2019, and 2018: Stock Options Year Ended December 31, 2020 2019 2018 Risk-free interest rate 0.4% - 0.5% 1.6% - 2.3% 1.2% - 3.1% Expected term (in years) 6.02 6.02 5.16-9.95 Volatility 76.5% - 78.5% 71.8% - 74.6% 58.7%-75.5% Dividend yield 0% 0% 0% ESPP Year Ended December 31, 2020 2019 2018 Risk-free interest rate 0.1% - 0.2% 1.6% - 2.3% 2.1% - 2.6% Expected term (in years) 0.5-2.0 0.5-2.0 0.5-2.0 Volatility 66.6% - 136.0% 64.8% - 77.1% 54.3% - 65.5% Dividend yield 0% 0% 0%

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss Per Share	The following table sets forth the computation of basic and diluted net loss per share (in thousands, except share and per share data): Year Ended December 31, 2020 2019 2018 Numerator: Net loss $ (122,858 ) $ (84,710 ) $ (49,594 ) Denominator: Weighted-average common shares outstanding 56,354,059 45,385,489 36,357,336 Less: weighted-average common shares subject to repurchase (1,566,941 ) (1,559,498 ) (1,739,099 ) Weighted-average common shares used to compute basic and diluted net loss per share 54,787,118 43,825,991 34,618,237 Net loss per share, basic and diluted $ (2.24 ) $ (1.93 ) $ (1.43 )
Summary of Outstanding Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss per Share	The following outstanding potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive: At December 31, 2020 2019 2018 Common stock options issued and outstanding 9,892,697 4,738,004 1,458,079 Unvested restricted stock issued as part of collaboration agreement 1,257,651 1,257,651 - Unvested early exercised common stock options 165,133 455,158 927,123 Unvested restricted stock units 738,650 - - Employee Stock Purchase Plan shares 18,219 - - Unvested restricted common stock - - 289,352 Total 12,072,350 6,450,813 2,674,554

Provision for Income Taxes (Tab

Provision for Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of Provision for Income Taxes Differs from Amount Expected by Applying Federal Statutory Rate to Loss Before Taxes	The provision for income taxes differs from the amount expected by applying the federal statutory rate to the loss before taxes as follows: Year Ended December 31, 2020 2019 2018 Federal statutory income tax rate 21.00 % 21.00 % 21.00 % Equity investment 4.15 % 0.00 % 0.00 % Research and development credits 3.10 % 0.00 % 0.00 % Change in valuation allowance (27.35 )% (19.65 )% (19.46 )% Non-deductible expenses and other (0.90 )% (1.35 )% (1.54 )% Total 0.00 % 0.00 % 0.00 %
Schedule of Components of Deferred Tax Assets	As of December 31, 2020 and 2019, the components of the Company’s deferred tax assets are as follows (in thousands): Year Ended December 31, 2020 2019 Deferred tax assets: Federal and state net operating loss carryforwards $ 54,526 $ 30,049 Research and development credits carryforwards 11,209 8,077 Depreciation 9,068 6,052 Deferred Revenue 2,407 3,277 Lease liability 3,831 - Other 5,890 2,965 Total deferred tax assets 86,931 50,420 Deferred tax liabilities: Right-of-use assets (2,704 ) - Total deferred tax liabilities (2,704 ) - Less valuation allowance (84,227 ) (50,420 ) Net deferred tax assets $ - $ -
Summary of Activity Related to Unrecognized Tax Benefits	The following table summarizes the activity related to our unrecognized tax benefits (in thousands): Year Ended December 31, 2020 2019 2018 Beginning balance $ 2,165 $ 1,084 $ 622 Additions (decreases) for tax positions taken in a prior year (258 ) (7 ) 8 Additions for tax positions taken in current year 1,246 1,088 454 Ending balance $ 3,153 $ 2,165 $ 1,084

Selected Unaudited Quarterly _2

Selected Unaudited Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Summary of Unaudited Quarterly Financial Data	The following table summarizes the Company’s unaudited quarterly financial data for the last two years (in thousands, except share and per share data): First Quarter Second Quarter Third Quarter Fourth Quarter 2020 Total revenues $ 1,750 $ 1,750 $ 64,530 $ 9,487 Total operating expenses $ 30,150 $ 47,125 $ 62,978 $ 61,499 Net income (loss) $ (27,753 ) $ (45,074 ) $ 1,822 $ (51,853 ) Net income (loss) per share — basic $ (0.63 ) $ (0.93 ) $ 0.03 $ (0.82 ) Net income (loss) per share — diluted $ (0.63 ) $ (0.93 ) $ 0.03 $ (0.82 ) Weighted average number of shares, basic 44,282,607 48,556,843 62,599,193 63,527,932 Weighted average number of shares, diluted 44,282,607 48,556,843 65,145,707 63,527,932 2019 Total revenues $ 1,750 $ 1,750 $ 1,750 $ 9,750 Total operating expenses $ 20,523 $ 30,910 $ 24,999 $ 27,277 Net loss $ (17,670 ) $ (28,090 ) $ (22,352 ) $ (16,598 ) Net loss per share — basic and diluted $ (0.41 ) $ (0.64 ) $ (0.51 ) $ (0.38 ) Weighted average number of shares, basic and diluted 43,508,592 43,797,718 43,939,281 44,056,407

Organization - Additional Infor

Organization - Additional Information (Details)	12 Months Ended
	Dec. 31, 2020Product
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of investigational product	4

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2020USD ($)Segment	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Jan. 01, 2020USD ($)
Significant Accounting Policies [Line Items]
Number of operating segments | Segment	1
Number of reportable segments | Segment	1
Impairment charges	$ 0	$ 0	$ 0
Trailer bill	0
Right-of-use assets	12,781,000
Operating lease, liabilities	18,110,000
Operating lease, current liabilities	2,867,000
Operating lease liabilities, noncurrent	15,243,000
Deferred rent balance		3,734,000
Accumulated deficit	$ (328,184,000)	$ (205,326,000)
ASU 2016-02
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
Change in Accounting Principle, Accounting Standards Update, Early Adoption [true false]	true
ASU 2018-18
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2018-13
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2018-15
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
ASU 2016-02
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Right-of-use assets				$ 5,800,000
Operating lease, liabilities				10,100,000
Operating lease, current liabilities				1,200,000
Operating lease liabilities, noncurrent				8,900,000
Deferred rent balance				4,300,000
ASU 2016-02 | Cumulative Effect, Period of Adoption, Adjustment
Significant Accounting Policies [Line Items]
Accumulated deficit				$ 0
ASU 2016-13
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true
Brisbane, California
Significant Accounting Policies [Line Items]
Operating lease expiration year	2031
Operating lease commencement year	2021
Minimum
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives	1 year
Operating lease expiration year	2025
Maximum
Significant Accounting Policies [Line Items]
Property and equipment, estimated useful lives	5 years
Operating lease expiration year	2029

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 173,415	$ 57,937
Restricted cash	203	203
Cash, cash equivalents and restricted cash	$ 173,618	$ 58,140	$ 71,267	$ 98,629

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair value assets transferred from level 1 to level 2	$ 0	$ 0
Fair value assets transferred from level 2 to level 1	0	0
Fair value liabilities transferred from level 1 to level 2	0	0
Fair value liabilities transferred from level 2 to level 1	0	0
Fair value assets transferred into level 3	0	0
Fair value assets transferred out of level 3	0	0
Fair value liabilities transferred into level 3	0	0
Fair value liabilities transferred out of level 3	0	0
Realized gains (loss) on sale or maturity of available-for-sale marketable securities		0	$ 0
Reclassification out of accumulated other comprehensive loss	$ 0	$ 0	$ 0

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Financial Instruments (Excluding Restricted Cash) Measured at Fair Value on Recurring Basis (Details) - Fair Value On Recurring Basis - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value	$ 735,086	$ 188,270
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value	146,468	45,498
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value	301,112	74,854
U.S. Government Agency Obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value	25,001
Corporate Securities and Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value	262,505	67,918
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value	146,468	45,498
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value	146,468	45,498
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value	588,618	142,772
Level 2 | U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value	301,112	74,854
Level 2 | U.S. Government Agency Obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value	25,001
Level 2 | Corporate Securities and Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total assets measured at fair value	$ 262,505	$ 67,918

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Investments Classified as Available for Sale Securities with Contractual Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Cash and cash equivalents	$ 173,415	$ 57,937
Short-term investments (due within one year)	555,231	130,333
Long-term investments (due between one and two years)	6,440
Total cash, cash equivalents and investments in marketable securities	$ 735,086	$ 188,270

Fair Value Measurements - Sch_3

Fair Value Measurements - Schedule of Fair Value and Amortized Cost of Investments in Marketable Securities by Major Security Type (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 735,042	$ 188,206
Unrealized Gain	57	67
Unrealized Loss	(13)	(3)
Fair Value	735,086	188,270
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	146,468	45,498
Fair Value	146,468	45,498
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	301,075	74,801
Unrealized Gain	38	12
Unrealized Loss	(1)	(1)
Fair Value	301,112	74,812
U.S. Government Agency Obligations
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	24,997
Unrealized Gain	4
Fair Value	25,001
Corporate Securities and Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	262,502	67,907
Unrealized Gain	15	55
Unrealized Loss	(12)	(2)
Fair Value	$ 262,505	$ 67,960

Consolidated Balance Sheet Co_3

Consolidated Balance Sheet Components - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Total	$ 25,095	$ 20,551
Less: Accumulated depreciation and amortization	(14,288)	(11,221)
Property and equipment, net	10,807	9,330
Scientific Equipment
Property Plant And Equipment [Line Items]
Total	9,902	8,168
Furniture and Equipment
Property Plant And Equipment [Line Items]
Total	1,521	1,165
Capitalized Software
Property Plant And Equipment [Line Items]
Total	225	146
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total	11,111	10,834
Construction in Progress
Property Plant And Equipment [Line Items]
Total	$ 2,336	$ 238

Consolidated Balance Sheet Co_4

Consolidated Balance Sheet Components - Summary of Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accrued Liabilities Current [Abstract]
Accrued personnel expenses	$ 8,632	$ 4,571
Professional fees	295	183
Other	616	196
Total other accrued liabilities	$ 9,543	$ 4,950

Equity Investment in PACT Pha_2

Equity Investment in PACT Pharma - Additional Information (Details) - USD ($) $ in Thousands, shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Gains on dilution of equity investment	$ 613		$ 1,229
Share of loss from equity method investee	(613)	$ (1,202)	$ (886)
PACT Pharma
Schedule of Equity Method Investments [Line Items]
Investment balance	0	0
Gains on dilution of equity investment	2,000
Share of loss from equity method investee	600	0
Operating losses on equity method investments	600	$ 1,200
Unrealized loss on equity method investments	1,300
PACT Pharma | Previously Reported
Schedule of Equity Method Investments [Line Items]
Losses on accumulated in prior periods of equity investment	$ 1,400
PACT Pharma | Series A Preferred Stock
Schedule of Equity Method Investments [Line Items]
Purchase of common stock, shares				1
PACT Pharma | Common Stock
Schedule of Equity Method Investments [Line Items]
Purchase of common stock, shares				3.6

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Dec. 31, 2020USD ($)ft²	Jun. 30, 2020USD ($)ft²	Dec. 31, 2020USD ($)ft²	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Lessee Lease Description [Line Items]
Operating lease, term of contract	10 years	8 years	10 years
Operating leases, minimum lease payments	$ 90,300	$ 10,100	$ 90,300	$ 13,391
Operating lease, option to extend	The lease is subject to two options to extend the lease term for a period of eight years each.	eight years
Operating lease, existence of option to extend	true	true
Operating lease, allowance for tenant improvements	$ 12,600	$ 1,000	$ 12,600
Operating lease, space delivered month and year			2020-08
Operating lease, option to extend lease term	8 years
Operating lease, option to increase allowance for tenant improvements	$ 5,500		$ 5,500
Weighted average remaining term	6 years 2 months 12 days		6 years 2 months 12 days
Operating lease, incremental borrowing rate				10.00%
Weighted average discount rate	7.30%		7.30%
Lease cost			$ 2,700
Short-term lease costs			200
Right-of-use assets	$ 12,781		12,781
Operating lease, liabilities	18,110		18,110
Short-term portion of operating lease liability	$ 2,867		$ 2,867
Operating lease, liability, current, statement of financial position [extensible list]	us-gaap:OtherCurrentLiabilitiesMember		us-gaap:OtherCurrentLiabilitiesMember
Operating lease liabilities, noncurrent	$ 15,243		$ 15,243
Rent expense				$ 1,600	$ 1,600
Operating lease Undiscounted amount	4,153		$ 4,153
Operating lease, lease not yet commenced, description			Total undiscounted future minimum lease payments do not include approximately $90.3 million related to the Company’s Brisbane lease that has not yet commenced.
Operating lease, leases commence year			2021
Minimum sublease rent income			$ 100
Operating lease, lease not yet commenced, existence of option to terminate			false
Deposits for letters of credit	$ 200		$ 200
Hayward, California
Lessee Lease Description [Line Items]
Square feet of space leased | ft²		36,303
Hayward, California | Executive Offices Research and Development and Business Operations
Lessee Lease Description [Line Items]
Square feet of space leased | ft²	136,293		136,293
Brisbane, California
Lessee Lease Description [Line Items]
Square feet of space leased | ft²	109,237		109,237
Operating lease expiration year			2031
Operating lease commencement year			2021
Operating lease Undiscounted amount	$ 90,300		$ 90,300
Minimum
Lessee Lease Description [Line Items]
Operating lease expiration year			2025
Minimum | Hayward, California | Executive Offices Research and Development and Business Operations
Lessee Lease Description [Line Items]
Operating lease expiration year			2025
Maximum
Lessee Lease Description [Line Items]
Operating lease expiration year			2029
Operating lease, lease not yet commenced, term of contract	10 years		10 years
Maximum | Hayward, California | Executive Offices Research and Development and Business Operations
Lessee Lease Description [Line Items]
Operating lease expiration year			2029

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Lease Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Leases [Abstract]
2020			$ 2,105
2021			2,195
2022			2,265
2023			2,339
2024			2,415
2025			2,072
Total undiscounted future minimum lease payments	$ 90,300	$ 10,100	$ 13,391
2021	4,041
2022	3,409
2023	3,522
2024	3,640
2025	3,340
Thereafter	4,311
Total undiscounted future minimum lease payments	22,263
Less: Imputed interest	(4,153)
Total operating lease liabilities	18,110
Less: Current portion of operating lease liabilities (included in other current liabilities)	(2,867)
Operating lease liabilities, noncurrent	$ 15,243

License and Collaboration Agr_3

License and Collaboration Agreements - Summary of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
License And Collaboration Agreements [Line Items]
License revenue	$ 9,487	$ 64,530	$ 1,750	$ 1,750	$ 9,750	$ 1,750	$ 1,750	$ 1,750
Gilead and Taiho | License
License And Collaboration Agreements [Line Items]
License revenue									$ 55,096	$ 8,000	$ 3,000
Gilead and Taiho | Collaboration Revenue
License And Collaboration Agreements [Line Items]
License revenue									22,421	7,000	5,353
Gilead and Taiho | Collaboration and License
License And Collaboration Agreements [Line Items]
License revenue									$ 77,517	$ 15,000	$ 8,353

License and Collaboration Agr_4

License and Collaboration Agreements - Summary of Revenues by Collaboration and by Category of Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	$ 77,517	$ 15,000	$ 8,353
Gilead License To Zimberelimab
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	55,096
Gilead Access Rights
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	15,421
Taiho License to Zimberelimab
License And Collaboration Agreements [Line Items]
Collaboration and license revenue		8,000
Taiho License to Etrumadenant
License And Collaboration Agreements [Line Items]
Collaboration and license revenue			3,000
Taiho Collaboration Agreement
License And Collaboration Agreements [Line Items]
Collaboration and license revenue	$ 7,000	$ 7,000	$ 5,353

License and Collaboration Agr_5

License and Collaboration Agreements - Summary of Revenue Recognized as a Result of Changes in Deferred Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
License And Collaboration Agreements [Abstract]
Amounts included in deferred revenue at the beginning of the period	$ 7,000	$ 7,000	$ 5,353

License and Collaboration Agr_6

License and Collaboration Agreements - Additional Information (Details)	Jul. 13, 2020USD ($)$ / sharesshares	Apr. 30, 2019USD ($)shares	Dec. 31, 2020USD ($)shares	Oct. 31, 2017USD ($)	Sep. 30, 2017USD ($)Program	Aug. 31, 2017USD ($)	Dec. 31, 2020USD ($)shares	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
License And Collaboration Agreements [Line Items]
Upfront cash payment							$ 175,000,000
Issuance of common stock							326,246,000		$ 124,735,000
Cost sharing receivable, current			$ 1,049,000				1,049,000	$ 132,000
Total collaboration and license revenues							77,517,000	15,000,000	8,353,000
Deferred revenue recognized							7,000,000	7,000,000	5,353,000
Deferred revenue, current			74,571,000				74,571,000	7,000,000
Deferred revenue, noncurrent			$ 122,830,000				122,830,000	12,022,000
Development expense							$ 159,348,000	78,481,000	49,646,000
Shares probable of vesting | shares			9,892,697				9,892,697
Stock Purchase Agreement
License And Collaboration Agreements [Line Items]
Direct offering cost	$ 1,900,000
Gilead | Gilead Collaboration Agreement
License And Collaboration Agreements [Line Items]
Upfront cash payment	175,000,000						$ 175,000,000
Unconstrained consideration to be received			$ 100,000,000				100,000,000
Premium on stock purchased	$ 90,600,000
Collaboration term for current and future clinical programs	10 years
Contingent milestone payments receivable	$ 400,000,000
Additional collaboration term for programs entering clinical development prior to end of collaboration term	3 years
Option fee per program for all other programs entering clinical development to exercise option	$ 150,000,000
Ongoing research and development support	400,000,000
Research and development information access rights payment related to year 2022	100,000,000
Initial transaction price	365,600,000
Option payment upon achievement of certain development milestones	250,000,000
Deferred revenue related to etrumadenant option			127,000,000				$ 127,000,000
Etrumadenant option initial term of agreement							4 years
Option payment upon achievement of certain development milestones	$ 275,000,000
Deferred revenue related to domvanalimab option			36,700,000				$ 36,700,000
Domvanalimab option recognized term							1 year
Current and future programs exclusive access period	10 years
Additional payment due at each of the fourth, sixth, and eighth anniversaries of the agreement	$ 100,000,000
Contingent milestone payment start period	2022
Contractual obligation for first payment	$ 100,000,000
Performance obligation period	4 years
Contractual obligation remaining amount not obligated to pay	$ 300,000,000
Deferred revenue related to research and development pipeline			121,700,000				$ 121,700,000
Future development and promotion costs contract liability			9,700,000				9,700,000
Consultant and legal fees	7,300,000
Amortization expense							200,000
Cost sharing receivable			4,200,000				4,200,000
Gilead | Gilead Collaboration Agreement | Prepaid Expenses and Other Current Assets
License And Collaboration Agreements [Line Items]
Cost sharing receivable, current			1,000,000				1,000,000
Gilead | Gilead Collaboration Agreement | Other Noncurrent Assets
License And Collaboration Agreements [Line Items]
Cost sharing receivable, noncurrent			3,200,000				3,200,000
Gilead | Gilead Collaboration Agreement | Maximum
License And Collaboration Agreements [Line Items]
Contingent milestone payments receivable	400,000,000
Option fee per program for current clinical programs to exercise option	275,000,000
Gilead | Gilead Collaboration Agreement | Minimum
License And Collaboration Agreements [Line Items]
Option fee per program for current clinical programs to exercise option	200,000,000
Gilead | Stock Purchase Agreement
License And Collaboration Agreements [Line Items]
Funds received for purchase of common stock							200,000,000
Fair value of stock purchased							109,400,000
Premium on stock purchased							90,600,000
Issuance of common stock	$ 200,000,000						$ 107,468,000
Issuance of common stock, shares | shares	5,963,029
Shares issued, price per share | $ / shares	$ 33.54
Percentage of option to purchase maximum shares of common stock	35.00%
Period over common stock to be purchased	5 years
Percentage of premium purchase price of common stock	20.00%
Trailing days average closing price	5 days
Share Price | $ / shares	$ 33.54
Taiho Pharmaceutical Co., Ltd | Taiho Agreement
License And Collaboration Agreements [Line Items]
Upfront cash payment					$ 20,000,000
Option period					5 years
Non refundable and non creditable cash payments										$ 35,000,000
Payment received for license agreement				$ 5,000,000				5,000,000	5,000,000	$ 25,000,000
Range of royalties receivable on net sales							high single-digits to mid-teens
Royalties payable description							Royalties will be payable on a licensed product-by-licensed product and country-by-country basis during the period of time commencing on the first commercial sale of a licensed product in a country and ending upon the later of: (a) ten (10) years from the date of first commercial sale of such licensed product in such country; and (b) expiration of the last-to-expire valid claim of the Company’s patents covering the manufacture, use or sale or exploitation of such licensed product in such country (the Royalty Term).
Non-refundable, non-creditable upfront cash payments							$ 35,000,000
Estimated performance period							5 years
Payment for first option exercise								8,000,000	3,000,000
Licensing revenue recognized								8,000,000
Clinical and regulatory milestones achieved							$ 0
Sales milestone or royalty revenue recognized							0
Total collaboration and license revenues							7,000,000	15,000,000
Deferred revenue recognized									8,300,000
Deferred revenue, current			7,000,000				7,000,000	7,000,000
Deferred revenue, noncurrent			5,000,000				$ 5,000,000	12,000,000
Taiho Pharmaceutical Co., Ltd | Taiho Agreement | Maximum
License And Collaboration Agreements [Line Items]
Contingent milestone payments receivable					$ 145,000,000
Extended option agreement period					7 years
Payment for option exercise					$ 15,000,000
Additional clinical and regulatory milestone payments receivable					$ 130,000,000
Taiho Pharmaceutical Co., Ltd | Taiho Agreement | Minimum
License And Collaboration Agreements [Line Items]
Number of programs, IND enabling studies not initiated | Program					5
Payment for option exercise					$ 3,000,000
WuXi Biologics License Agreement
License And Collaboration Agreements [Line Items]
Clinical and regulatory milestones achieved			16,500,000
Range of tiered royalty payments on net sales							high single-digits to low teens
WuXi Biologics License Agreement | Research and Development
License And Collaboration Agreements [Line Items]
Upfront cash payment			$ 500,000
Milestone payments							$ 5,000,000	7,500,000	0
Sub-license fees incurred							10,100,000	1,200,000	0
WuXi Biologics License Agreement | Maximum
License And Collaboration Agreements [Line Items]
Clinical, regulatory and commercialization milestone payments						$ 375,000,000
Abmuno License Agreement
License And Collaboration Agreements [Line Items]
Development expense								0
Abmuno License Agreement | Research and Development
License And Collaboration Agreements [Line Items]
Milestone payments							3		$ 2,800,000
Abmuno License Agreement | Maximum
License And Collaboration Agreements [Line Items]
Clinical, regulatory and commercialization remaining milestone payments							98,000,000
Genentech
License And Collaboration Agreements [Line Items]
Development expense							500,000	0
Strata Oncology Inc | Co-Development and Collaboration Agreement
License And Collaboration Agreements [Line Items]
Development milestone payable		$ 2,500,000
Development cost recorded within research and development expenses							1,700,000	1,000,000
Development cost reimbursed							$ 300,000	200,000
Number of restricted shares of common stock issued | shares		1,257,651
Fair value of restricted shares of common stock issued		$ 15,000,000
Strata Oncology Inc | Co-Development and Collaboration Agreement | Non-vested Restricted Stock
License And Collaboration Agreements [Line Items]
Shares probable of vesting | shares			0				0
Compensation expense recognized							$ 0
Strata Oncology Inc | Co-Development and Collaboration Agreement | Research and Development
License And Collaboration Agreements [Line Items]
Milestone payments							$ 0	$ 2,500,000
Strata Oncology Inc | Co-Development and Collaboration Agreement | Maximum
License And Collaboration Agreements [Line Items]
Regulatory and commercial milestone payable		$ 125,000,000

License and Collaboration Agr_7

License and Collaboration Agreements - Schedule of Payments Allocated to Performance Obligations (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Allocation of transaction price
Upfront cash consideration	$ 175,000
Payment for access rights related to the Company's research and development pipeline	100,000
Premium from Stock Purchase Agreement	90,600
Total transaction price allocated to revenue	365,600
Allocation to performance obligations
Zimberelimab license	55,096
Etrumadenant option	126,960
Domvanalimab option	36,728
Access rights related to the Company's research and development pipeline	137,113
Development and commercialization services for zimberelimab	9,703
Total	$ 365,600

Convertible Preferred Stock a_2

Convertible Preferred Stock and Stockholders' Equity (Deficit) - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 13, 2020	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2017
Class Of Stock [Line Items]
Capital stock shares authorized			410,000,000
Common stock, shares authorized			400,000,000		400,000,000
Preferred stock, shares authorized			10,000,000		10,000,000
Common stock, par value			$ 0.0001		$ 0.0001
Preferred stock, par value			$ 0.0001		$ 0.0001
Net proceeds from public offering after deducting underwriting discounts, commissions and other offering expenses			$ 433,776
Common stock share value			$ 326,246	$ 124,735
Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares outstanding			0		0	30,459,574
Stock Purchase Agreement | Gilead
Class Of Stock [Line Items]
Common stock shares issued	5,963,029
Shares issued, price per share	$ 33.54
Net proceeds from public offering after deducting underwriting discounts, commissions and other offering expenses	$ 107,500
Common stock share value	200,000		$ 107,468
Purchase price of common stock allocation to performance obligation	90,600
Deferred offering expenses	$ 1,900
May 2020 Public Offering
Class Of Stock [Line Items]
Common stock shares issued		12,650,000
Shares issued, price per share		$ 27.50
Net proceeds from public offering after deducting underwriting discounts, commissions and other offering expenses		$ 326,200
Base Shares
Class Of Stock [Line Items]
Common stock shares issued		11,000,000
Underwriters Option Exercise
Class Of Stock [Line Items]
Common stock shares issued		1,650,000

Stock Plans and Stock-Based C_3

Stock Plans and Stock-Based Compensation - Additional Information (Details) - USD ($)	Jan. 01, 2021	Jan. 01, 2019	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2015	Nov. 30, 2020	Jan. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Intrinsic value of shares exercised				$ 6,800,000	$ 200,000	$ 600,000
Fair value of shares vested				$ 16,800,000	$ 7,800,000	$ 3,000,000
Options granted				5,784,550
Common stock, shares outstanding				65,114,685	45,925,004
Share-based compensation, vested stock options				31,986	372,774	14,918
Description of expected term simplified method				The Company has opted to use the “simplified method” for estimating the expected term of options, whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the option (generally 10 years).
Expected term				10 years
Expected dividend yield				0.00%
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period							4 years
Estimated fair value, price per share							$ 0.0004
Vesting interval period							monthly
Options granted				0	0	0
Total grant date fair value of shares granted				$ 21,100,000	$ 0	$ 0
Total grant date fair value of shares vested				100,000	$ 0	$ 0
Unrecognized employee compensation costs				$ 88,900,000
Non-vested stock option recognized weighted average period				2 years 10 months 24 days
Restricted Stock Units | Chief Executive Officer and President
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued							2,777,776
Price per share							$ 0.0004
Non-Employee Stock-Based Compensation
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares not vested and subject to repurchase				21,165	308,596	31,388
Stock based compensation expense				$ 700,000	$ 900,000	$ 300,000
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized employee compensation costs				$ 88,900,000
Non-vested stock option recognized weighted average period				2 years 10 months 24 days
Expected term				6 years 7 days	6 years 7 days
Expected dividend yield				0.00%	0.00%	0.00%
Maximum | Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term						9 years 11 months 12 days
Minimum | Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term						5 years 1 month 28 days
2015 Stock Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares not vested and subject to repurchase				165,133	455,158
Cash received from early exercise of unvested options				$ 700,000	$ 1,700,000
Award vesting period				48 months
Total shares of authorized common stock reserved for future issuance			709,558
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued or transferred			3,570,000
Total shares of authorized common stock reserved for future issuance				1,106,209
2018 Equity Incentive Plan | Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares not vested and subject to repurchase				738,650
2018 Equity Incentive Plan | Restricted Stock Units | Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period				4 years
Vesting interval period				annually or quarterly
2018 Equity Incentive Plan | Restricted Stock Units | Directors
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting interval period				annually
2018 Equity Incentive Plan | Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock reserved for issuance under evergreen provision	2,604,587
2018 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock reserved for issuance under evergreen provision		3,570,000
Percentage of common stock outstanding		4.00%
2020 Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares issued or transferred								1,000,000	3,000,000
Total shares of authorized common stock reserved for future issuance				784,975
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase date of fair market value trading days			24 months
Total shares of authorized common stock reserved for future issuance			714,000	1,190,422
2018 Employee Stock Purchase Plan | Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock reserved for issuance under evergreen provision	651,146
2018 Employee Stock Purchase Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of common stock as percentage of market value			85.00%
Number of shares of common stock that may be purchased by an employee on any purchase date			3,000
Number of shares that may be purchased in any calendar year			$ 25,000
Percentage of common stock shares outstanding		1.00%
Common stock, shares outstanding		1,071,000

Stock Plans and Stock-Based C_4

Stock Plans and Stock-Based Compensation - Summary of Option Activity Includes Options Granted (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)$ / sharesshares
Shares Subject to Outstanding Options
Beginning balance | shares	4,738,004
Options granted | shares	5,784,550
Options exercised | shares	(392,523)
Options forfeited or canceled | shares	(237,334)
Ending balance | shares	9,892,697
Options vested and expected to vest as of December 31, 2020 | shares	9,892,697
Options exercisable as of December 31, 2020 | shares	2,793,050
Weighted Average Exercise Price Per Share
Beginning balance | $ / shares	$ 9
Options granted | $ / shares	17.36
Options exercised | $ / shares	8.54
Options forfeited or canceled | $ / shares	10.38
Ending balance | $ / shares	13.88
Options vested and expected to vest as of December 31, 2020 | $ / shares	13.88
Options exercisable as of December 31, 2020 | $ / shares	$ 10.28
Weighted Average Remaining Contractual Term (in years)	8 years 9 months 21 days
Options vested and expected to vest, Weighted Average Remaining Contractual Term (in years)	8 years 9 months 21 days
Options exercisable, Weighted Average Remaining Contractual Term (in years)	8 years 1 month 13 days
Aggregate Intrinsic Value | $	$ 122,232
Options vested and expected to vest, Aggregate Intrinsic Value | $	122,232
Options exercisable, Aggregate Intrinsic Value | $	$ 44,012

Stock Plans and Stock-Based C_5

Stock Plans and Stock-Based Compensation - Summary of Restricted Stock Units Activity (Details) - 2018 Equity Incentive Plan - Restricted Stock Units	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Total Restricted Stock Units
RSUs granted | shares	758,950
RSUs vested | shares	(6,250)
RSUs forfeited or canceled | shares	(14,050)
Nonvested at December 31, 2020 | shares	738,650
Weighted Average Grant Date Fair Value
RSUs granted | $ / shares	$ 27.77
RSUs vested | $ / shares	17
RSUs forfeited or canceled | $ / shares	29.05
Nonvested at December 31, 2020 | $ / shares	$ 27.84

Stock Plans and Stock-Based C_6

Stock Plans and Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - Employee And Non Employee - 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]
Total stock-based compensation	$ 21,825	$ 8,981	$ 3,874
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	11,195	4,152	2,255
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 10,630	$ 4,829	$ 1,619

Stock Plans and Stock-Based C_7

Stock Plans and Stock-Based Compensation - Assumptions used to Calculate Fair Value of Stock-Based Compensation (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Expected term (in years)	10 years
Dividend yield	0.00%
Employee Stock Option
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Risk-free interest rate, minimum	0.40%	1.60%	1.20%
Risk-free interest rate, maximum	0.50%	2.30%	3.10%
Expected term (in years)	6 years 7 days	6 years 7 days
Volatility, minimum	76.50%	71.80%	58.70%
Volatility, maximum	78.50%	74.60%	75.50%
Dividend yield	0.00%	0.00%	0.00%
ESPP
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Risk-free interest rate, minimum	0.10%	1.60%	2.10%
Risk-free interest rate, maximum	0.20%	2.30%	2.60%
Volatility, minimum	66.60%	64.80%	54.30%
Volatility, maximum	136.00%	77.10%	65.50%
Dividend yield	0.00%	0.00%	0.00%
Minimum | Employee Stock Option
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Expected term (in years)			5 years 1 month 28 days
Minimum | ESPP
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Expected term (in years)	6 months	6 months	6 months
Maximum | Employee Stock Option
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Expected term (in years)			9 years 11 months 12 days
Maximum | ESPP
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Expected term (in years)	2 years	2 years	2 years

Net Loss per Share - Computatio

Net Loss per Share - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss	$ (51,853)	$ 1,822	$ (45,074)	$ (27,753)	$ (16,598)	$ (22,352)	$ (28,090)	$ (17,670)	$ (122,858)	$ (84,710)	$ (49,594)
Denominator:
Weighted-average common shares outstanding									56,354,059	45,385,489	36,357,336
Less: weighted-average common shares subject to repurchase									(1,566,941)	(1,559,498)	(1,739,099)
Weighted-average common shares used to compute basic and diluted net loss per share					44,056,407	43,939,281	43,797,718	43,508,592	54,787,118	43,825,991	34,618,237
Net loss per share, basic and diluted									$ (2.24)	$ (1.93)	$ (1.43)

Net Loss per Share - Summary of

Net Loss per Share - Summary of Outstanding Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss per Share (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]
Antidilutive securities excluded from computation of diluted net loss per share	12,072,350	6,450,813	2,674,554
Common Stock Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	9,892,697	4,738,004	1,458,079
Unvested Restricted Stock Issued as Part of Collaboration Agreement
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	1,257,651	1,257,651
Unvested Early Exercised Common Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	165,133	455,158	927,123
Unvested Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	738,650
Employee Stock Purchase Plan Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	18,219
Unvested Restricted Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share			289,352

Provision for Income Taxes - Sc

Provision for Income Taxes - Schedule of Provision for Income Taxes Differs from Amount Expected by Applying Federal Statutory Rate to Loss Before Taxes (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	21.00%	21.00%
Equity investment	4.15%	0.00%	0.00%
Research and development credits	3.10%	0.00%	0.00%
Change in valuation allowance	(27.35%)	(19.65%)	(19.46%)
Non-deductible expenses and other	(0.90%)	(1.35%)	(1.54%)
Total	0.00%	0.00%	0.00%

Provision for Income Taxes - _2

Provision for Income Taxes - Schedule of Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Federal and state net operating loss carryforwards	$ 54,526	$ 30,049
Research and development credits carryforwards	11,209	8,077
Depreciation	9,068	6,052
Deferred Revenue	2,407	3,277
Lease liability	3,831
Other	5,890	2,965
Total deferred tax assets	86,931	50,420
Deferred tax liabilities:
Right-of-use assets	(2,704)
Total deferred tax liabilities	(2,704)
Less valuation allowance	$ (84,227)	$ (50,420)

Provision for Income Taxes - Ad

Provision for Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Valuation allowance increased value	$ 33,800,000	$ 19,700,000	$ 12,200,000
Net operating loss carryforwards	253,300,000
Interest or penalties accrued	0	0	0
Liability related to uncertain tax positions	0
Reserve for unrecognized tax benefits	3,153,000	$ 2,165,000	$ 1,084,000	$ 622,000
Federal
Income Taxes [Line Items]
Net operating loss carryforwards	$ 47,400,000
Net operating loss carryforwards, expiration year	2035
Net operating loss carryforwards amount with no expiration date	$ 205,900,000
Federal | Earliest Tax Year | U.S.
Income Taxes [Line Items]
Open tax year	2015
Federal | Latest Tax Year | U.S.
Income Taxes [Line Items]
Open tax year	2019
Federal | Research
Income Taxes [Line Items]
Research tax credits	$ 9,900,000
Research tax credits, expiration year	2035
State
Income Taxes [Line Items]
Net operating loss carryforwards	$ 15,900,000
Net operating loss carryforwards, expiration year	2035
State | Earliest Tax Year | California
Income Taxes [Line Items]
Open tax year	2015
State | Latest Tax Year | California
Income Taxes [Line Items]
Open tax year	2019
State | Research
Income Taxes [Line Items]
Research tax credits	$ 5,100,000
Foreign Tax Authority | Earliest Tax Year | Australian Taxation Office
Income Taxes [Line Items]
Open tax year	2017
Foreign Tax Authority | Latest Tax Year | Australian Taxation Office
Income Taxes [Line Items]
Open tax year	2019

Provision for Income Taxes - Su

Provision for Income Taxes - Summary of Activity Related to Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation Of Unrecognized Tax Benefits Excluding Amounts Pertaining To Examined Tax Returns Roll Forward
Beginning balance	$ 2,165	$ 1,084	$ 622
Additions (decreases) for tax positions taken in a prior year	(258)	(7)	8
Additions for tax positions taken in current year	1,246	1,088	454
Ending balance	$ 3,153	$ 2,165	$ 1,084

Commitments - Additional Inform

Commitments - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Purchase commitments cancellation notice period	30 days
Liabilities for Indemnification rights and agreements	$ 0	$ 0

Related Parties - Additional In

Related Parties - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 13, 2020	May 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Cost sharing receivable			$ 1,049	$ 132
Deferred revenue, noncurrent ($117,808 and $0 to a related party)			122,830	12,022
Upfront cash payment			175,000
Research and Development
Related Party Transaction [Line Items]
Reimbursed under cost-sharing provisions of arrangement			3,446	$ 0	$ 0
Gilead Collaboration Agreement | Gilead
Related Party Transaction [Line Items]
Upfront cash payment	$ 175,000		175,000
Unconstrained consideration to be received			100,000
Premium on stock purchased	$ 90,600
Stock Purchase Agreement | Gilead
Related Party Transaction [Line Items]
Issuance of common stock, shares	5,963,029
Funds received for purchase of common stock			200,000
Fair value of stock purchased			109,400
Premium on stock purchased			$ 90,600
Gilead
Related Party Transaction [Line Items]
Percentage of outstanding common stock held			13.00%
Price per share		$ 27.50
Value of common stock issued		$ 56,700
Number of shares issued		2,200,000
Cost sharing receivable			$ 900
Deferred revenue			185,400
Deferred revenue, noncurrent ($117,808 and $0 to a related party)			117,800
Future development and commercialization services contract liability			9,700
Gilead | Research and Development
Related Party Transaction [Line Items]
Reimbursed under cost-sharing provisions of arrangement			3,400
Gilead | Gilead Collaboration Agreement
Related Party Transaction [Line Items]
Revenue recognized			$ 70,500
Gilead | Stock Purchase Agreement
Related Party Transaction [Line Items]
Issuance of common stock, shares	5,963,029
Gilead | Maximum
Related Party Transaction [Line Items]
Right to purchase additional outstanding voting common stock percentage			35.00%

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Defined contribution plan, percentage of employee compensation allowed to be contributed	100.00%
Defined contribution plan, cost	$ 0	$ 0	$ 0

Selected Unaudited Quarterly _3

Selected Unaudited Quarterly Financial Data - Summary of Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 9,487	$ 64,530	$ 1,750	$ 1,750	$ 9,750	$ 1,750	$ 1,750	$ 1,750
Total operating expenses	61,499	62,978	47,125	30,150	27,277	24,999	30,910	20,523	$ 201,752	$ 103,709	$ 63,212
Net income (loss)	$ (51,853)	$ 1,822	$ (45,074)	$ (27,753)	$ (16,598)	$ (22,352)	$ (28,090)	$ (17,670)	$ (122,858)	$ (84,710)	$ (49,594)
Net income (loss) per share — basic	$ (0.82)	$ 0.03	$ (0.93)	$ (0.63)
Net income (loss) per share — diluted	$ (0.82)	$ 0.03	$ (0.93)	$ (0.63)
Weighted average number of shares, basic	63,527,932	62,599,193	48,556,843	44,282,607
Weighted average number of shares, diluted	63,527,932	65,145,707	48,556,843	44,282,607
Net loss per share — basic and diluted					$ (0.38)	$ (0.51)	$ (0.64)	$ (0.41)	$ (2.24)	$ (1.93)	$ (1.43)
Weighted average number of shares, basic and diluted					44,056,407	43,939,281	43,797,718	43,508,592	54,787,118	43,825,991	34,618,237

Subsequent Event - Additional I

Subsequent Event - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 24, 2021	Dec. 31, 2020	Dec. 31, 2019
Subsequent Event [Line Items]
Number of additional shares purchased		65,114,685	45,925,004
Proceeds from sale of additional shares of common stock		$ 433,776
Gilead | Subsequent Event
Subsequent Event [Line Items]
Number of additional shares purchased	5,650,000
Purchase price per share	$ 39
Proceeds from sale of additional shares of common stock	$ 220,400
Percentage of ownership	19.50%