Summary of Significant Accounting Policies (Policies)	12 Months Ended
Dec. 31, 2022
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Consolidated Financial Statements, which include the accounts of Arcus as well as its wholly owned subsidiary, 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. All intercompany transactions and balances have been eliminated in consolidation. We assess whether we are the primary beneficiary of a variable interest entity (“VIE”) at the inception of the arrangement and at each reporting date. This assessment is based on our power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and our obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. We do not have any significant interests in any variable interest entities of which we are the primary beneficiary.
Use of Estimates	Use of Estimates The preparation of the 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 and related disclosures. We base our estimates on historical experience and on various market-specific and other relevant assumptions that we believe to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Estimates are assessed each period and updated to reflect current information. Actual results may differ materially from those estimates.
Collaborative Arrangements	Collaborative Arrangements We assess whether our licensing and other agreements are collaborative arrangements based on whether they involve joint operating activities and whether both parties have active participation in the arrangement and are exposed to significant risks and rewards. For arrangements that we determine are collaborations, we identify each distinct performance obligation, and then determine whether a customer relationship exists for that distinct performance obligation. If we determine a performance obligation within the collaborative arrangement to be with a customer, we apply our revenue accounting policy. If a portion of a distinct bundle of goods or services within the collaborative arrangement is not with a customer, we apply recognition and measurement based on an analogy to authoritative accounting literature or, if there is no appropriate analogy, a reasonable, rational, and consistently applied accounting policy election.
Revenues	Revenues We recognize revenue when a customer obtains control of promised goods or services in a contract for an amount that reflects the consideration we expect to receive in exchange for those goods or services. For contracts with customers, we perform the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) we satisfy each performance obligation. We only apply the five-step model to contracts when it is probable that we will collect the consideration we are entitled to in exchange for the goods or services we transfer to the customer. As part of the accounting for contracts with customers, we develop assumptions that require judgment to determine the standalone selling price of each performance obligation identified in the contract. In addition, variable consideration such as milestone payments are evaluated to determine if they are constrained and, therefore, excluded from the transaction price. We then allocate the total transaction price proportionally to each performance obligation based on their estimated standalone selling prices. We then recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. We currently do not have product sales and our revenues are derived from arrangements for the development of our investigational products. Such arrangements may require us to deliver various rights, services and/or goods, including intellectual property rights/licenses, R&D services, manufacturing services and/or commercialization services. The underlying terms of these arrangements may generally include consideration to Arcus in the form of one or more of the following: (i) nonrefundable, up-front 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) profit sharing. In arrangements involving more than one performance obligation, each performance obligation is evaluated to determine whether it qualifies as distinct based on whether (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available and (ii) the good or service is separately identifiable from other promises in the contract. The consideration under the arrangement is then allocated to each separate distinct performance obligation based on its respective relative stand-alone selling price. The estimated selling price of each deliverable reflects our best estimate of what the selling price would be if the deliverable was regularly sold by us on a stand-alone basis or by using an adjusted market assessment approach if selling price on a stand-alone basis is not available. The consideration allocated to each distinct performance obligation is recognized as revenue when control of the related goods is transferred or services are performed. We evaluate each performance obligation to determine if it can be satisfied at a point in time or over time as services are performed. For performance obligations that are determined to be satisfied over time we determine an appropriate method of measuring progress for purposes of recognizing revenue. Consideration associated with at-risk substantive performance milestones is recognized as revenue when it is probable that a significant reversal of the cumulative revenue recognized will not occur. For arrangements that include sales-based royalties, including milestone payments based on sales thresholds, and for which the license is deemed to be the predominant item to which the royalties relate, we 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). To date, we have not recognized any royalty revenue resulting from any of our arrangements. The accounting for these arrangements requires us to develop estimates and assumptions that require judgment. These estimates may include items such as forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. Actual results may differ materially from those estimates. See Note 5, Revenues, for more information.
Research and Development Expenses	Research and Development Expenses Research and development (“R&D”) costs are expensed as incurred and primarily include: salaries, benefits and other staff-related costs; facilities and overhead costs; third-party service provider costs for preclinical and clinical studies; laboratory supplies and equipment maintenance costs; consulting; payments under collaborative and other arrangements including milestone payments, licenses and fees; expense reimbursements to collaboration partners; and other related expenses. Under certain collaborative arrangements, we are reimbursed for a portion of the research and development expenses, including costs of drug supplies. When these R&D expenses are incurred under a reimbursement or cost sharing model with a collaboration partner, we record the related reimbursements as a reduction of R&D expense in our Consolidated Statements of Operations. Acquired in-process research and development projects with no alternative future use are recorded in R&D expense upon acquisition. Net payment or reimbursement of R&D costs is recognized when the obligations are incurred or as we become entitled to the cost recovery. See Note 4, License and collaboration agreements, for more information. Clinical study costs are a significant component of R&D expenses. Our clinical studies are primarily performed by third-party contract research organizations (“CROs”). We monitor levels of performance under each significant contract including the extent of patient enrollment and other activities and accrue costs for clinical studies performed over the service periods specified in the contract. We adjust our estimates, if required, based upon our ongoing review of the level of effort and costs actually incurred by the CROs. All of our material CRO contracts are terminable by us upon written notice, and we are generally only liable for actual services completed by the CRO and certain noncancelable expenses incurred at termination.
General and Administrative Expenses	General and Administrative Expenses General and administrative (“G&A”) expenses relate to: finance; human resources; legal and other administrative activities which consist primarily of personnel costs; facilities and overhead costs; legal expenses; and other general and administrative costs. G&A expenses also include cost recoveries associated with collaborative R&D arrangements.
Stock-Based Compensation	Stock-Based Compensation We provide share-based compensation in the form of various types of equity-based awards, including restricted stock units (“RSU”s) and stock options. The fair values of RSU’s and stock options, which are subject to service conditions and vesting, are recognized as compensation expense on a straight-line basis over the service period net of forfeitures as they occur. See Note 8, Stock-based compensation, for more information.
Income Taxes	Income Taxes We provide 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, 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 we determine it is more likely than not that some or all of the tax benefits will not be realized. We recognize the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained upon examination by tax authorities. We assess all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and we will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate. We include any penalties and interest expense related to income taxes as a component of other expense and interest income, net, as necessary. See Note 6, Income taxes, for more information.
Cash Equivalents	Cash Equivalents Cash equivalents consist of marketable securities having an original maturity of three months or less at the time of purchase.
Marketable Securities	Marketable securities We consider our interest-bearing securities investment portfolio as available-for-sale, and accordingly, these investments are recorded at fair value, with unrealized gains and losses recorded in Accumulated Other Comprehensive Income (AOCI). See Note 10, Cash, cash equivalents and marketable securities, and Note 15, Fair value measurements, for more information.
Property and Equipment	Property and Equipment Property and equipment is recorded at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from three to ten years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. We review 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. See Note 11, Property and equipment, for more information.
Leases	Leases We determine whether an arrangement is or contains a lease at contract inception. Operating lease right-of-use assets and lease liabilities are recognized at the commencement date based on the present value of the lease payments over the lease term, which is the non-cancelable period stated in the contract adjusted for any options to extend or terminate when it is reasonably certain that we will exercise that option. Right-of-use assets are adjusted for prepaid lease payments, lease incentives and initial direct costs incurred. Operating lease expense for the minimum lease payments is recognized on a straight-line basis over the lease term. When our operating leases do not provide an implicit interest rate, we generally utilize our incremental borrowing rate, based on the information available at the commencement date to determine the lease liability. We do not recognize the right-of-use assets and liabilities for leases with lease terms of one year or less with payments recognized as operating expenses on a straight-line basis over the lease term. See Note 13, Leases, for more information.
Fair Value of Financial Instruments	Fair Value of Financial Instruments We apply fair value accounting for all financial and non-financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. We define fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities which are required to be recorded at fair value, we consider the principal or most advantageous market in which we would transact and the market-based risk measurements or assumptions that market participants would use in pricing the asset or liability, such as risks inherent in valuation techniques, transfer restrictions and credit risks. See Note 15, Fair value measurements, for more information.
Other Significant Accounting Policies	Other Significant Accounting Policies Our other significant accounting policies are described in the remaining appropriate notes to the Consolidated Financial Statements.
Recent Accounting Pronouncements	Recent Accounting Pronouncements There have been no new accounting pronouncements issued or adopted during the year ended December 31, 2022 with a significant impact to our financial statements.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2022

The Consolidated Financial Statements, which include the accounts of Arcus as well as its wholly owned subsidiary, 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. All intercompany transactions and balances have been eliminated in consolidation.

We assess whether we are the primary beneficiary of a variable interest entity (“VIE”) at the inception of the arrangement and at each reporting date. This assessment is based on our power to direct the activities of the VIE that most significantly impact the VIE’s economic performance and our obligation to absorb losses or the right to receive benefits from the VIE that could potentially be significant to the VIE. We do not have any significant interests in any variable interest entities of which we are the primary beneficiary.

Use of Estimates

The preparation of the 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 and related disclosures. We base our estimates on historical experience and on various market-specific and other relevant assumptions that we believe to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Estimates are assessed each period and updated to reflect current information. Actual results may differ materially from those estimates.

Collaborative Arrangements

We assess whether our licensing and other agreements are collaborative arrangements based on whether they involve joint operating activities and whether both parties have active participation in the arrangement and are exposed to significant risks and rewards. For arrangements that we determine are collaborations, we identify each distinct performance obligation, and then determine whether a customer relationship exists for that distinct performance obligation. If we determine a performance obligation within the collaborative arrangement to be with a customer, we apply our revenue accounting policy. If a portion of a distinct bundle of goods or services within the collaborative arrangement is not with a customer, we apply recognition and measurement based on an analogy to authoritative accounting literature or, if there is no appropriate analogy, a reasonable, rational, and consistently applied accounting policy election.

Revenues

We recognize revenue when a customer obtains control of promised goods or services in a contract for an amount that reflects the consideration we expect to receive in exchange for those goods or services. For contracts with customers, we perform the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) we satisfy each performance obligation. We only apply the five-step model to contracts when it is probable that we will collect the consideration we are entitled to in exchange for the goods or services we transfer to the customer. As part of the accounting for contracts with customers, we develop assumptions that require judgment to determine the standalone selling price of
each performance obligation identified in the contract. In addition, variable consideration such as milestone payments are evaluated to determine if they are constrained and, therefore, excluded from the transaction price. We then allocate the total transaction price proportionally to each performance obligation based on their estimated standalone selling prices. We then recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.

We currently do not have product sales and our revenues are derived from arrangements for the development of our investigational products. Such arrangements may require us to deliver various rights, services and/or goods, including intellectual property rights/licenses, R&D services, manufacturing services and/or commercialization services. The underlying terms of these arrangements may generally include consideration to Arcus in the form of one or more of the following: (i) nonrefundable, up-front 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) profit sharing.

In arrangements involving more than one performance obligation, each performance obligation is evaluated to determine whether it qualifies as distinct based on whether (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available and (ii) the good or service is separately identifiable from other promises in the contract. The consideration under the arrangement is then allocated to each separate distinct performance obligation based on its respective relative stand-alone selling price. The estimated selling price of each deliverable reflects our best estimate of what the selling price would be if the deliverable was regularly sold by us on a stand-alone basis or by using an adjusted market assessment approach if selling price on a stand-alone basis is not available. The consideration allocated to each distinct performance obligation is recognized as revenue when control of the related goods is transferred or services are performed. We evaluate each performance obligation to determine if it can be satisfied at a point in time or over time as services are performed. For performance obligations that are determined to be satisfied over time we determine an appropriate method of measuring progress for purposes of recognizing revenue.

Consideration associated with at-risk substantive performance milestones is recognized as revenue when it is probable that a significant reversal of the cumulative revenue recognized will not occur.

For arrangements that include sales-based royalties, including milestone payments based on sales thresholds, and for which the license is deemed to be the predominant item to which the royalties relate, we 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). To date, we have not recognized any royalty revenue resulting from any of our arrangements.

The accounting for these arrangements requires us to develop estimates and assumptions that require judgment. These estimates may include items such as forecasted revenues or costs, development timelines, discount rates, and probabilities of technical and regulatory success. Actual results may differ materially from those estimates.

See Note 5, Revenues, for more information.

Research and Development Expenses

Research and development (“R&D”) costs are expensed as incurred and primarily include: salaries, benefits and other staff-related costs; facilities and overhead costs; third-party service provider costs for preclinical and clinical studies; laboratory supplies and equipment maintenance costs; consulting; payments under collaborative and other arrangements including milestone payments, licenses and fees; expense reimbursements to collaboration partners; and other related expenses. Under certain collaborative arrangements, we are reimbursed for a portion of the research and development expenses, including costs of drug supplies. When these R&D expenses are incurred under a reimbursement or cost sharing model with a collaboration partner, we record the related reimbursements as a reduction of R&D expense in our Consolidated Statements of Operations. Acquired in-process research and development projects with no alternative future use are recorded in R&D expense upon acquisition.

Net payment or reimbursement of R&D costs is recognized when the obligations are incurred or as we become entitled to the cost recovery. See Note 4, License and collaboration agreements, for more information.

Clinical study costs are a significant component of R&D expenses. Our clinical studies are primarily performed by third-party contract research organizations (“CROs”). We monitor levels of performance under each significant contract including the extent of patient enrollment and other activities and accrue costs for clinical studies performed over the service periods specified in the contract. We adjust our estimates, if required, based upon our ongoing review of the level of effort and costs actually incurred by the CROs. All of our material CRO contracts are terminable by us upon written notice, and we are generally only liable for actual services completed by the CRO and certain noncancelable expenses incurred at termination.

General and Administrative Expenses

General and administrative (“G&A”) expenses relate to: finance; human resources; legal and other administrative activities which consist primarily of personnel costs; facilities and overhead costs; legal expenses; and other general and administrative costs. G&A expenses also include cost recoveries associated with collaborative R&D arrangements.

Stock-Based Compensation

We provide share-based compensation in the form of various types of equity-based awards, including restricted stock units (“RSU”s) and stock options. The fair values of RSU’s and stock options, which are subject to service conditions and vesting, are recognized as compensation expense on a straight-line basis over the service period net of forfeitures as they occur. See Note 8, Stock-based compensation, for more information.

Income Taxes

We provide 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, 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 we determine it is more likely than not that some or all of the tax benefits will not be realized.

We recognize the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained upon examination by tax authorities. We assess all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and we will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate.

We include any penalties and interest expense related to income taxes as a component of other expense and interest income, net, as necessary.

See Note 6, Income taxes, for more information.

Cash Equivalents

Cash equivalents consist of marketable securities having an original maturity of three months or less at the time of purchase.

Marketable Securities

Marketable securities

We consider our interest-bearing securities investment portfolio as available-for-sale, and accordingly, these investments are recorded at fair value, with unrealized gains and losses recorded in Accumulated Other Comprehensive Income (AOCI). See Note 10, Cash, cash equivalents and marketable securities, and Note 15, Fair value measurements, for more information.

Property and Equipment

Property and equipment is recorded at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from three to ten years. Leasehold improvements are amortized over the shorter of their estimated useful lives or the related lease term. We review 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. See Note 11, Property and equipment, for more information.

Leases

We determine whether an arrangement is or contains a lease at contract inception. Operating lease right-of-use assets and lease liabilities are recognized at the commencement date based on the present value of the lease payments over the lease term, which is the non-cancelable period stated in the contract adjusted for any options to extend or terminate when it is reasonably certain that we will exercise that option. Right-of-use assets are adjusted for prepaid lease payments, lease incentives and initial direct costs incurred. Operating lease expense for the minimum lease payments is recognized on a straight-line basis over the lease term. When our operating leases do not provide an implicit interest rate, we generally utilize our incremental borrowing rate, based on the information available at the commencement date to determine the lease liability. We do not recognize the right-of-use assets and liabilities for leases with lease terms of one year or less with payments recognized as operating expenses on a straight-line basis over the lease term. See Note 13, Leases, for more information.

Fair Value of Financial Instruments

We apply fair value accounting for all financial and non-financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. We define fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities which are required to be recorded at fair value, we consider the principal or most advantageous market in which we would transact and the market-based risk measurements or assumptions that market participants would use in pricing the asset or liability, such as risks inherent in valuation techniques, transfer restrictions and credit risks. See Note 15, Fair value measurements, for more information.

Other Significant Accounting Policies

Our other significant accounting policies are described in the remaining appropriate notes to the Consolidated Financial Statements.

Recent Accounting Pronouncements

There have been no new accounting pronouncements issued or adopted during the year ended December 31, 2022 with a significant impact to our financial statements.