<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.26.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>190</ContextCount>
  <ElementCount>233</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>63</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>8</UnitCount>
  <MyReports>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0000001 - Document - Cover</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/Cover</Role>
      <ShortName>Cover</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>9952151 - Statement - Condensed Consolidated Statements of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedStatementsofOperations</Role>
      <ShortName>Condensed Consolidated Statements of Operations</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>9952152 - Statement - Condensed Consolidated Statements of Operations (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedStatementsofOperationsParenthetical</Role>
      <ShortName>Condensed Consolidated Statements of Operations (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>9952153 - Statement - Condensed Consolidated Statements of Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedStatementsofComprehensiveLoss</Role>
      <ShortName>Condensed Consolidated Statements of Comprehensive Loss</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>9952154 - Statement - Condensed Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedBalanceSheets</Role>
      <ShortName>Condensed Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>9952155 - Statement - Condensed Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Condensed Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>9952156 - Statement - Condensed Consolidated Statements of Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedStatementsofStockholdersEquity</Role>
      <ShortName>Condensed Consolidated Statements of Stockholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>9952157 - Statement - Condensed Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedStatementsofCashFlows</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>9952158 - Statement - Condensed Consolidated Statements of Cash Flows (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedStatementsofCashFlowsParenthetical</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>9952159 - Disclosure - Organization, Liquidity and Capital Resources</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/OrganizationLiquidityandCapitalResources</Role>
      <ShortName>Organization, Liquidity and Capital Resources</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>9952160 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/SummaryofSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>9952161 - Disclosure - Related Party - Gilead Sciences, Inc.</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/RelatedPartyGileadSciencesInc</Role>
      <ShortName>Related Party - Gilead Sciences, Inc.</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>9952162 - Disclosure - License and Collaborations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/LicenseandCollaborations</Role>
      <ShortName>License and Collaborations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>9952163 - Disclosure - Revenues</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/Revenues</Role>
      <ShortName>Revenues</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>9952164 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>9952165 - Disclosure - Net Loss Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/NetLossPerShare</Role>
      <ShortName>Net Loss Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>9952166 - Disclosure - Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/StockBasedCompensation</Role>
      <ShortName>Stock-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>9952167 - Disclosure - Cash, Cash Equivalents and Marketable Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CashCashEquivalentsandMarketableSecurities</Role>
      <ShortName>Cash, Cash Equivalents and Marketable Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>9952168 - Disclosure - Condensed Consolidated Balance Sheet Components</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedBalanceSheetComponents</Role>
      <ShortName>Condensed Consolidated Balance Sheet Components</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>9952169 - Disclosure - Long-Term Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/LongTermDebt</Role>
      <ShortName>Long-Term Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>9952170 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/Leases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>9952171 - Disclosure - Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/StockholdersEquity</Role>
      <ShortName>Stockholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>9952172 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/FairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>9952173 - Disclosure - Business Segment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/BusinessSegment</Role>
      <ShortName>Business Segment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>9955511 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/SummaryofSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://arcusbio.com/role/SummaryofSignificantAccountingPolicies</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>9955512 - Disclosure - Revenues (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/RevenuesTables</Role>
      <ShortName>Revenues (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://arcusbio.com/role/Revenues</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>9955513 - Disclosure - Net Loss Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/NetLossPerShareTables</Role>
      <ShortName>Net Loss Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://arcusbio.com/role/NetLossPerShare</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>9955514 - Disclosure - Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/StockBasedCompensationTables</Role>
      <ShortName>Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://arcusbio.com/role/StockBasedCompensation</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>9955515 - Disclosure - Cash, Cash Equivalents and Marketable Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CashCashEquivalentsandMarketableSecuritiesTables</Role>
      <ShortName>Cash, Cash Equivalents and Marketable Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://arcusbio.com/role/CashCashEquivalentsandMarketableSecurities</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>9955516 - Disclosure - Condensed Consolidated Balance Sheet Components (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedBalanceSheetComponentsTables</Role>
      <ShortName>Condensed Consolidated Balance Sheet Components (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://arcusbio.com/role/CondensedConsolidatedBalanceSheetComponents</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>9955517 - Disclosure - Long-Term Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/LongTermDebtTables</Role>
      <ShortName>Long-Term Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://arcusbio.com/role/LongTermDebt</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>9955518 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/LeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://arcusbio.com/role/Leases</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>9955519 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://arcusbio.com/role/FairValueMeasurements</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>9955520 - Disclosure - Business Segment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/BusinessSegmentTables</Role>
      <ShortName>Business Segment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://arcusbio.com/role/BusinessSegment</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>9955521 - Disclosure - Organization, Liquidity and Capital Resources - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/OrganizationLiquidityandCapitalResourcesAdditionalInformationDetails</Role>
      <ShortName>Organization, Liquidity and Capital Resources - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>9955522 - Disclosure - Related Party - Gilead Sciences, Inc. (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/RelatedPartyGileadSciencesIncDetails</Role>
      <ShortName>Related Party - Gilead Sciences, Inc. (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://arcusbio.com/role/RelatedPartyGileadSciencesInc</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>9955523 - Disclosure - License and Collaborations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/LicenseandCollaborationsDetails</Role>
      <ShortName>License and Collaborations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://arcusbio.com/role/LicenseandCollaborations</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>9955524 - Disclosure - Revenues - Summary of Revenues by Collaboration, Category of Revenue and Method of Recognition (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/RevenuesSummaryofRevenuesbyCollaborationCategoryofRevenueandMethodofRecognitionDetails</Role>
      <ShortName>Revenues - Summary of Revenues by Collaboration, Category of Revenue and Method of Recognition (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>9955525 - Disclosure - Revenues - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/RevenuesAdditionalInformationDetails</Role>
      <ShortName>Revenues - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>9955526 - Disclosure - Revenues - Summary of Revenue Recognized as a Result of Changes in Deferred Revenue (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/RevenuesSummaryofRevenueRecognizedasaResultofChangesinDeferredRevenueDetails</Role>
      <ShortName>Revenues - Summary of Revenue Recognized as a Result of Changes in Deferred Revenue (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>9955527 - Disclosure - Revenues - Summary of Transaction Price and Allocation of Transaction Price to the Performance Obligations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/RevenuesSummaryofTransactionPriceandAllocationofTransactionPricetothePerformanceObligationsDetails</Role>
      <ShortName>Revenues - Summary of Transaction Price and Allocation of Transaction Price to the Performance Obligations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>9955528 - Disclosure - Net Loss Per Share - Summary of Outstanding Potentially Dilutive Securities Excluded from Computation of Diluted Net Income (Loss) per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/NetLossPerShareSummaryofOutstandingPotentiallyDilutiveSecuritiesExcludedfromComputationofDilutedNetIncomeLossperShareDetails</Role>
      <ShortName>Net Loss Per Share - Summary of Outstanding Potentially Dilutive Securities Excluded from Computation of Diluted Net Income (Loss) per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>9955529 - Disclosure - Stock-Based Compensation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/StockBasedCompensationDetails</Role>
      <ShortName>Stock-Based Compensation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://arcusbio.com/role/StockBasedCompensationTables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>9955530 - Disclosure - Cash, Cash Equivalents and Marketable Securities - Summary of Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Our Cash, Cash Equivalents and Marketable Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CashCashEquivalentsandMarketableSecuritiesSummaryofAmortizedCostGrossUnrealizedGainsandLossesandFairValueofOurCashCashEquivalentsandMarketableSecuritiesDetails</Role>
      <ShortName>Cash, Cash Equivalents and Marketable Securities - Summary of Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Our Cash, Cash Equivalents and Marketable Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>9955531 - Disclosure - Cash, Cash Equivalents and Marketable Securities - Summary of Fair Values of Our Cash, Cash Equivalents and Marketable Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CashCashEquivalentsandMarketableSecuritiesSummaryofFairValuesofOurCashCashEquivalentsandMarketableSecuritiesDetails</Role>
      <ShortName>Cash, Cash Equivalents and Marketable Securities - Summary of Fair Values of Our Cash, Cash Equivalents and Marketable Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>9955532 - Disclosure - Cash, Cash Equivalents and Marketable Securities - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CashCashEquivalentsandMarketableSecuritiesAdditionalInformationDetails</Role>
      <ShortName>Cash, Cash Equivalents and Marketable Securities - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>9955533 - Disclosure - Cash, Cash Equivalents and Marketable Securities - Summary of Cash, Cash Equivalents and Restricted Cash (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CashCashEquivalentsandMarketableSecuritiesSummaryofCashCashEquivalentsandRestrictedCashDetails</Role>
      <ShortName>Cash, Cash Equivalents and Marketable Securities - Summary of Cash, Cash Equivalents and Restricted Cash (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>9955534 - Disclosure - Condensed Consolidated Balance Sheet Components - Summary of Prepaid and Other Current Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedBalanceSheetComponentsSummaryofPrepaidandOtherCurrentAssetsDetails</Role>
      <ShortName>Condensed Consolidated Balance Sheet Components - Summary of Prepaid and Other Current Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>9955535 - Disclosure - Condensed Consolidated Balance Sheet Components - Summary of Other Current Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/CondensedConsolidatedBalanceSheetComponentsSummaryofOtherCurrentLiabilitiesDetails</Role>
      <ShortName>Condensed Consolidated Balance Sheet Components - Summary of Other Current Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>9955536 - Disclosure - Long-Term Debt - Summary of Long-Term Debt Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/LongTermDebtSummaryofLongTermDebtInstrumentsDetails</Role>
      <ShortName>Long-Term Debt - Summary of Long-Term Debt Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>9955537 - Disclosure - Long-Term Debt - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/LongTermDebtAdditionalInformationDetails</Role>
      <ShortName>Long-Term Debt - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>9955538 - Disclosure - Leases - Summary of Cash and Non-cash Information Related to Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/LeasesSummaryofCashandNoncashInformationRelatedtoOperatingLeasesDetails</Role>
      <ShortName>Leases - Summary of Cash and Non-cash Information Related to Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>9955539 - Disclosure - Leases - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/LeasesAdditionalInformationDetails</Role>
      <ShortName>Leases - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>9955540 - Disclosure - Stockholders' Equity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/StockholdersEquityDetails</Role>
      <ShortName>Stockholders' Equity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://arcusbio.com/role/StockholdersEquity</ParentRole>
      <Position>55</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>9955541 - Disclosure - Fair Value Measurements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/FairValueMeasurementsDetails</Role>
      <ShortName>Fair Value Measurements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://arcusbio.com/role/FairValueMeasurementsTables</ParentRole>
      <Position>56</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>9955542 - Disclosure - Business Segment - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/BusinessSegmentAdditionalInformationDetails</Role>
      <ShortName>Business Segment - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="rcus-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>9955543 - Disclosure - Business Segment - Summary of Segment Reporting Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://arcusbio.com/role/BusinessSegmentSummaryofSegmentReportingInformationDetails</Role>
      <ShortName>Business Segment - Summary of Segment Reporting Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" isDefinitelyFs="true" isUsgaap="true" original="rcus-20260331.htm">rcus-20260331.htm</File>
    <File>rcus-20260331.xsd</File>
    <File>rcus-20260331_cal.xml</File>
    <File>rcus-20260331_def.xml</File>
    <File>rcus-20260331_lab.xml</File>
    <File>rcus-20260331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles>
    <File>rcus-20260331_g1.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="442">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="29">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="25">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
