<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.22.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>176</ContextCount>
  <ElementCount>449</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>63</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>100000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>100010 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/StatementConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>100020 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/StatementConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>100030 - Statement - Consolidated Statements of Operations and Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/StatementConsolidatedStatementsOfOperationsAndComprehensiveLoss</Role>
      <ShortName>Consolidated Statements of Operations and Comprehensive Loss</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>100040 - Statement - Consolidated Statements of Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/StatementConsolidatedStatementsOfStockholdersEquity</Role>
      <ShortName>Consolidated Statements of Stockholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>100050 - Statement - Consolidated Statements of Stockholders' Equity (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/StatementConsolidatedStatementsOfStockholdersEquityParenthetical</Role>
      <ShortName>Consolidated Statements of Stockholders' Equity (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>100060 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/StatementConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>100070 - Statement - Consolidated Statements of Cash Flows (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/StatementConsolidatedStatementsOfCashFlowsParenthetical</Role>
      <ShortName>Consolidated Statements of Cash Flows (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>100080 - Disclosure - Nature of the Business and Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureNatureOfBusinessAndBasisOfPresentation</Role>
      <ShortName>Nature of the Business and Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>100090 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>100100 - Disclosure - Fair Value Measurements of Financial Assets and Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureFairValueMeasurementsOfFinancialAssetsAndLiabilities</Role>
      <ShortName>Fair Value Measurements of Financial Assets and Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>100110 - Disclosure - Property and Equipment, Net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosurePropertyAndEquipmentNet</Role>
      <ShortName>Property and Equipment, Net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>100120 - Disclosure - Accrued Expenses and Other Current Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureAccruedExpensesAndOtherCurrentLiabilities</Role>
      <ShortName>Accrued Expenses and Other Current Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>100130 - Disclosure - Kiq, LLC Acquisition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureKiqLLCAcquisition</Role>
      <ShortName>Kiq, LLC Acquisition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>100140 - Disclosure - Sale of BOXR Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureSaleOfBOXRAssets</Role>
      <ShortName>Sale of BOXR Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>100150 - Disclosure - Preferred Stock, Series A Non-Voting Convertible Preferred Stock and Common Stock</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosurePreferredStockSeriesANonVotingConvertiblePreferredStockAndCommonStock</Role>
      <ShortName>Preferred Stock, Series A Non-Voting Convertible Preferred Stock and Common Stock</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>100160 - Disclosure - Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureStockBasedCompensation</Role>
      <ShortName>Stock-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>100170 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>100180 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>100190 - Disclosure - Net Loss Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureNetLossPerShare</Role>
      <ShortName>Net Loss Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>100200 - Disclosure - Retirement Plan</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureRetirementPlan</Role>
      <ShortName>Retirement Plan</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>100210 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>100220 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>100230 - Disclosure - Fair Value Measurements of Financial Assets and Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureFairValueMeasurementsOfFinancialAssetsAndLiabilitiesTables</Role>
      <ShortName>Fair Value Measurements of Financial Assets and Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureFairValueMeasurementsOfFinancialAssetsAndLiabilities</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>100240 - Disclosure - Property and Equipment, Net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosurePropertyAndEquipmentNetTables</Role>
      <ShortName>Property and Equipment, Net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cogentbio.com/20211231/taxonomy/role/DisclosurePropertyAndEquipmentNet</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>100250 - Disclosure - Accrued Expenses and Other Current Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureAccruedExpensesAndOtherCurrentLiabilitiesTables</Role>
      <ShortName>Accrued Expenses and Other Current Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureAccruedExpensesAndOtherCurrentLiabilities</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>100260 - Disclosure - Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureStockBasedCompensationTables</Role>
      <ShortName>Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureStockBasedCompensation</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>100270 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureIncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureIncomeTaxes</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>100280 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>100290 - Disclosure - Net Loss per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureNetLossPerShareTables</Role>
      <ShortName>Net Loss per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>100300 - Disclosure - Nature of the Business and Basis of Presentation - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureNatureOfBusinessAndBasisOfPresentationAdditionalInformationDetail</Role>
      <ShortName>Nature of the Business and Basis of Presentation - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>100310 - Disclosure - Summary of Significant Accounting Policies - Schedule of Estimated Useful Life (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesScheduleOfEstimatedUsefulLifeDetail</Role>
      <ShortName>Summary of Significant Accounting Policies - Schedule of Estimated Useful Life (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>100320 - Disclosure - Summary of Significant Accounting Policies - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetail</Role>
      <ShortName>Summary of Significant Accounting Policies - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>100330 - Disclosure - Fair Value Measurements of Financial Assets and Liabilities - Schedule of Financial Assets and Liabilities at Fair Value on Recurring Basis (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureFairValueMeasurementsOfFinancialAssetsAndLiabilitiesScheduleOfFinancialAssetsAndLiabilitiesAtFairValueOnRecurringBasisDetail</Role>
      <ShortName>Fair Value Measurements of Financial Assets and Liabilities - Schedule of Financial Assets and Liabilities at Fair Value on Recurring Basis (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>100340 - Disclosure - Fair Value Measurements of Financial Assets and Liabilities - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureFairValueMeasurementsOfFinancialAssetsAndLiabilitiesAdditionalInformationDetail</Role>
      <ShortName>Fair Value Measurements of Financial Assets and Liabilities - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>100350 - Disclosure - Fair Value Measurements of Financial Assets and Liabilities - Summary of Changes in the Fair Value of Company's CVR Liability (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureFairValueMeasurementsOfFinancialAssetsAndLiabilitiesSummaryOfChangesInFairValueOfCompanySCVRLiabilityDetail</Role>
      <ShortName>Fair Value Measurements of Financial Assets and Liabilities - Summary of Changes in the Fair Value of Company's CVR Liability (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>100360 - Disclosure - Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosurePropertyAndEquipmentNetScheduleOfPropertyAndEquipmentNetDetail</Role>
      <ShortName>Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>100370 - Disclosure - Property Plant Equipment Net - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosurePropertyPlantEquipmentNetAdditionalInformationDetail</Role>
      <ShortName>Property Plant Equipment Net - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>100380 - Disclosure - Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureAccruedExpensesAndOtherCurrentLiabilitiesScheduleOfAccruedExpensesAndOtherCurrentLiabilitiesDetail</Role>
      <ShortName>Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>100390 - Disclosure - Kiq, LLC Acquisition - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureKiqLLCAcquisitionAdditionalInformationDetail</Role>
      <ShortName>Kiq, LLC Acquisition - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>100400 - Disclosure - Sale of BOXR Assets - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureSaleOfBOXRAssetsAdditionalInformationDetail</Role>
      <ShortName>Sale of BOXR Assets - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>100410 - Disclosure - Preferred Stock, Series A Non-Voting Convertible Preferred Stock and Common Stock - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosurePreferredStockSeriesANonVotingConvertiblePreferredStockAndCommonStockAdditionalInformationDetail</Role>
      <ShortName>Preferred Stock, Series A Non-Voting Convertible Preferred Stock and Common Stock - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>100420 - Disclosure - Stock-Based Compensation - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetail</Role>
      <ShortName>Stock-Based Compensation - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>100430 - Disclosure - Stock-Based Compensation - Schedule of Fair Value Option Granted (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureStockBasedCompensationScheduleOfFairValueOptionGrantedDetail</Role>
      <ShortName>Stock-Based Compensation - Schedule of Fair Value Option Granted (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>100440 - Disclosure - Stock-Based Compensation - Schedule of Common Stock Option Activity (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureStockBasedCompensationScheduleOfCommonStockOptionActivityDetail</Role>
      <ShortName>Stock-Based Compensation - Schedule of Common Stock Option Activity (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>100450 - Disclosure - Stock-Based Compensation - Summary of Information Pertaining to Stock Purchase Rights Granted under Employee Stock Purchase Plan (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureStockBasedCompensationSummaryOfInformationPertainingToStockPurchaseRightsGrantedUnderEmployeeStockPurchasePlanDetail</Role>
      <ShortName>Stock-Based Compensation - Summary of Information Pertaining to Stock Purchase Rights Granted under Employee Stock Purchase Plan (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>100460 - Disclosure - Stock-Based Compensation - Schedule of Stock-based Compensation Expense by Type of Award (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureStockBasedCompensationScheduleOfStockBasedCompensationExpenseByTypeOfAwardDetail</Role>
      <ShortName>Stock-Based Compensation - Schedule of Stock-based Compensation Expense by Type of Award (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>100470 - Disclosure - Stock-Based Compensation - Schedule of Stock Based Compensation Expense (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureStockBasedCompensationScheduleOfStockBasedCompensationExpenseDetail</Role>
      <ShortName>Stock-Based Compensation - Schedule of Stock Based Compensation Expense (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>100480 - Disclosure - Income Taxes - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureIncomeTaxesAdditionalInformationDetail</Role>
      <ShortName>Income Taxes - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>100490 - Disclosure - Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureIncomeTaxesScheduleOfEffectiveIncomeTaxRateReconciliationDetail</Role>
      <ShortName>Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>100500 - Disclosure - Income Taxes - Schedule of Deferred Tax Assets (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureIncomeTaxesScheduleOfDeferredTaxAssetsDetail</Role>
      <ShortName>Income Taxes - Schedule of Deferred Tax Assets (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>100510 - Disclosure - Income Taxes - Changes in Valuation Allowance for Deferred Tax Assets (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureIncomeTaxesChangesInValuationAllowanceForDeferredTaxAssetsDetail</Role>
      <ShortName>Income Taxes - Changes in Valuation Allowance for Deferred Tax Assets (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>100520 - Disclosure - Commitments and Contingencies - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetail</Role>
      <ShortName>Commitments and Contingencies - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>100530 - Disclosure - Commitments and Contingencies - Summary of Elements of Lease Expense Net of Sublease Income (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureCommitmentsAndContingenciesSummaryOfElementsOfLeaseExpenseNetOfSubleaseIncomeDetail</Role>
      <ShortName>Commitments and Contingencies - Summary of Elements of Lease Expense Net of Sublease Income (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>100540 - Disclosure - Commitments and Contingencies - Summary of Future Minimum Payments under Operating Lease (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureCommitmentsAndContingenciesSummaryOfFutureMinimumPaymentsUnderOperatingLeaseDetail</Role>
      <ShortName>Commitments and Contingencies - Summary of Future Minimum Payments under Operating Lease (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>100560 - Disclosure - Net Loss Per Share - Schedule of Earnings Per Share Basic and Diluted (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureNetLossPerShareScheduleOfEarningsPerShareBasicAndDilutedDetail</Role>
      <ShortName>Net Loss Per Share - Schedule of Earnings Per Share Basic and Diluted (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>100570 - Disclosure - Net Loss Per Share - Summary of Potential Dilutive Securities (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureNetLossPerShareSummaryOfPotentialDilutiveSecuritiesDetail</Role>
      <ShortName>Net Loss Per Share - Summary of Potential Dilutive Securities (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="cogt-10k_20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>100580 - Disclosure - Retirement Plan - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cogentbio.com/20211231/taxonomy/role/DisclosureRetirementPlanAdditionalInformationDetail</Role>
      <ShortName>Retirement Plan - Additional Information (Detail)</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-K" original="cogt-10k_20211231.htm">cogt-10k_20211231.htm</File>
    <File>cogt-20211231.xsd</File>
    <File>cogt-20211231_cal.xml</File>
    <File>cogt-20211231_def.xml</File>
    <File>cogt-20211231_lab.xml</File>
    <File>cogt-20211231_pre.xml</File>
    <File>cogt-ex101_639.htm</File>
    <File>cogt-ex104_638.htm</File>
    <File>cogt-ex211_10.htm</File>
    <File>cogt-ex231_13.htm</File>
    <File>cogt-ex311_12.htm</File>
    <File>cogt-ex312_9.htm</File>
    <File>cogt-ex321_14.htm</File>
    <File>cogt-ex322_6.htm</File>
    <File>cogt-ex41_7.htm</File>
  </InputFiles>
  <SupplementalFiles>
    <File>grdcseqcwpmf000001.jpg</File>
    <File>grdcseqcwpmf000002.jpg</File>
    <File>grdcseqcwpmf000003.jpg</File>
    <File>grdcseqcwpmf000004.jpg</File>
    <File>grdcseqcwpmf000005.jpg</File>
    <File>grdcseqcwpmf000006.jpg</File>
    <File>grdcseqcwpmf000007.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="534">http://fasb.org/us-gaap/2021-01-31</BaseTaxonomy>
    <BaseTaxonomy items="39">http://xbrl.sec.gov/dei/2021q4</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
