<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.21.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>122</ContextCount>
  <ElementCount>324</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>50</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>100000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>100010 - Statement - Condensed Consolidated Balance Sheets (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited</Role>
      <ShortName>Condensed Consolidated Balance Sheets (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>100020 - Statement - Condensed Consolidated Balance Sheets (unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnauditedParenthetical</Role>
      <ShortName>Condensed Consolidated Balance Sheets (unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>100030 - Statement - Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsAndComprehensiveLossUnaudited</Role>
      <ShortName>Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>100040 - Statement - Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity/Deficit (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfRedeemableConvertiblePreferredStockAndStockholdersEquityDeficitUnaudited</Role>
      <ShortName>Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity/Deficit (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>100050 - Statement - Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity/Deficit (Unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfRedeemableConvertiblePreferredStockAndStockholdersEquityDeficitUnauditedParenthetical</Role>
      <ShortName>Condensed Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity/Deficit (Unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>100060 - Statement - Condensed Consolidated Statements of Cash Flows (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>100070 - Disclosure - Nature of Business and Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureNatureOfBusinessAndBasisOfPresentation</Role>
      <ShortName>Nature of Business and Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>100080 - Disclosure - Summary of significant accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of significant accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>100090 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureFairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>100100 - Disclosure - Supplemental Balance Sheet Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureSupplementalBalanceSheetInformation</Role>
      <ShortName>Supplemental Balance Sheet Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>100110 - Disclosure - License and collaboration agreements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureLicenseAndCollaborationAgreements</Role>
      <ShortName>License and collaboration agreements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>100120 - Disclosure - Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureGovernmentGrantFundingAndPotentialRepaymentCommitmentsUnderRecoverableCashAdvanceGrantsRcas</Role>
      <ShortName>Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>100130 - Disclosure - Stockholders??? equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureStockholdersEquity</Role>
      <ShortName>Stockholders??? equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>100140 - Disclosure - Stock-based compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureStockBasedCompensation</Role>
      <ShortName>Stock-based compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>100150 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>100160 - Disclosure - Related party transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactions</Role>
      <ShortName>Related party transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>100170 - Disclosure - Net Loss Per Share Attributable to Common Stock</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureNetLossPerShareAttributableToCommonStock</Role>
      <ShortName>Net Loss Per Share Attributable to Common Stock</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>100180 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureSubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>100190 - Disclosure - Summary of significant accounting policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of significant accounting policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>100200 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureFairValueMeasurements</ParentRole>
      <Position>21</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>100210 - Disclosure - Supplemental Balance Sheet Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureSupplementalBalanceSheetInformationTables</Role>
      <ShortName>Supplemental Balance Sheet Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureSupplementalBalanceSheetInformation</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>100220 - Disclosure - Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureGovernmentGrantFundingAndPotentialRepaymentCommitmentsUnderRecoverableCashAdvanceGrantsRcasTables</Role>
      <ShortName>Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureGovernmentGrantFundingAndPotentialRepaymentCommitmentsUnderRecoverableCashAdvanceGrantsRcas</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>100230 - Disclosure - Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureStockBasedCompensationTables</Role>
      <ShortName>Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>100240 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>100250 - Disclosure - Net Loss Per Share Attributable to Common Stock (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureNetLossPerShareAttributableToCommonStockTables</Role>
      <ShortName>Net Loss Per Share Attributable to Common Stock (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureNetLossPerShareAttributableToCommonStock</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>100260 - Disclosure - Nature of Business and Basis of Presentation - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureNatureOfBusinessAndBasisOfPresentationAdditionalInformationDetails</Role>
      <ShortName>Nature of Business and Basis of Presentation - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>100270 - Disclosure - Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on a Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialInstrumentsMeasuredAtFairValueOnRecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on a Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>100280 - Disclosure - Fair Value Measurements - Summary of Fair Value of Series B Preferred Stock Tranche Rights Liability (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFairValueOfSeriesBPreferredStockTrancheRightsLiabilityDetails</Role>
      <ShortName>Fair Value Measurements - Summary of Fair Value of Series B Preferred Stock Tranche Rights Liability (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>100290 - Disclosure - Fair Value Measurements - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsAdditionalInformationDetails</Role>
      <ShortName>Fair Value Measurements - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>100300 - Disclosure - Fair Value Measurements - Summary of Changes in Level 3 Liabilities Measures at Fair Value on a Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfChangesInLevel3LiabilitiesMeasuresAtFairValueOnRecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements - Summary of Changes in Level 3 Liabilities Measures at Fair Value on a Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>100310 - Disclosure - Supplemental Balance Sheet Information - Schedule of Property and Equipment, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureSupplementalBalanceSheetInformationScheduleOfPropertyAndEquipmentNetDetails</Role>
      <ShortName>Supplemental Balance Sheet Information - Schedule of Property and Equipment, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>100320 - Disclosure - Supplemental Balance Sheet Information - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureSupplementalBalanceSheetInformationAdditionalInformationDetails</Role>
      <ShortName>Supplemental Balance Sheet Information - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>100330 - Disclosure - Supplemental Balance Sheet Information - Schedule of Accrued Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureSupplementalBalanceSheetInformationScheduleOfAccruedExpensesDetails</Role>
      <ShortName>Supplemental Balance Sheet Information - Schedule of Accrued Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>100340 - Disclosure - License and collaboration agreements - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureLicenseAndCollaborationAgreementsAdditionalInformationDetails</Role>
      <ShortName>License and collaboration agreements - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>100350 - Disclosure - Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs) - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureGovernmentGrantFundingAndPotentialRepaymentCommitmentsUnderRecoverableCashAdvanceGrantsRcasAdditionalInformationDetails</Role>
      <ShortName>Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs) - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureGovernmentGrantFundingAndPotentialRepaymentCommitmentsUnderRecoverableCashAdvanceGrantsRcasTables</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>100360 - Disclosure - Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs) - Schedule of Activity for Grant Programs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureGovernmentGrantFundingAndPotentialRepaymentCommitmentsUnderRecoverableCashAdvanceGrantsRcasScheduleOfActivityForGrantProgramsDetails</Role>
      <ShortName>Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs) - Schedule of Activity for Grant Programs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureGovernmentGrantFundingAndPotentialRepaymentCommitmentsUnderRecoverableCashAdvanceGrantsRcasTables</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>100370 - Disclosure - Stockholders' equity - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureStockholdersEquityAdditionalInformationDetails</Role>
      <ShortName>Stockholders' equity - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>100380 - Disclosure - Stock-based compensation - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails</Role>
      <ShortName>Stock-based compensation - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>100390 - Disclosure - Stock-based compensation - Summary of Stock-Based Compensation Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfStockBasedCompensationExpenseDetails</Role>
      <ShortName>Stock-based compensation - Summary of Stock-Based Compensation Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>100400 - Disclosure - Stock-based compensation - Summary of Stock Options Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfStockOptionsActivityDetails</Role>
      <ShortName>Stock-based compensation - Summary of Stock Options Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>100410 - Disclosure - Stock-based compensation - Schedule of Fair Value Assumptions for Stock Options Granted (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureStockBasedCompensationScheduleOfFairValueAssumptionsForStockOptionsGrantedDetails</Role>
      <ShortName>Stock-based compensation - Schedule of Fair Value Assumptions for Stock Options Granted (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>100420 - Disclosure - Commitments and Contingencies - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetails</Role>
      <ShortName>Commitments and Contingencies - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>100430 - Disclosure - Commitments and Contingencies - Schedule Of Lease Terms And Discount Rate (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureCommitmentsAndContingenciesScheduleOfLeaseTermsAndDiscountRateDetails</Role>
      <ShortName>Commitments and Contingencies - Schedule Of Lease Terms And Discount Rate (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>100440 - Disclosure - Commitments and Contingencies -Schedule Of Cash Flow And Other Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureCommitmentsAndContingenciesScheduleOfCashFlowAndOtherInformationDetails</Role>
      <ShortName>Commitments and Contingencies -Schedule Of Cash Flow And Other Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>100450 - Disclosure - Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureCommitmentsAndContingenciesScheduleOfFutureMinimumLeasePaymentsUnderNonCancelableOperatingLeasesDetails</Role>
      <ShortName>Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>100470 - Disclosure - Related Party Transactions - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails</Role>
      <ShortName>Related Party Transactions - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>100480 - Disclosure - Net Loss Per Share Attributable to Common Stock - Schedule of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureNetLossPerShareAttributableToCommonStockScheduleOfCommonStockEquivalentsExcludedFromCalculationOfDilutedNetLossPerShareDetails</Role>
      <ShortName>Net Loss Per Share Attributable to Common Stock - Schedule of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="itos-20210331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>100490 - Disclosure - Subsequent Events - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.iteostherapeutics.com/20210331/taxonomy/role/DisclosureSubsequentEventsAdditionalInformationDetails</Role>
      <ShortName>Subsequent Events - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>itos-20210331.xml</File>
    <File>itos-20210331.xsd</File>
    <File>itos-20210331_cal.xml</File>
    <File>itos-20210331_def.xml</File>
    <File>itos-20210331_lab.xml</File>
    <File>itos-20210331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://xbrl.sec.gov/country/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/stpr/2018-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
