<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.22.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>294</ContextCount>
  <ElementCount>445</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>92</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>6</UnitCount>
  <MyReports>
    <Report instance="fa-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://fadv.com/20211231/taxonomy/role/Role_DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>100010 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_StatementConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>100040 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_StatementConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>100060 - Statement - Consolidated Statements of Operations and Comprehensive Income (Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_StatementConsolidatedStatementsOfOperationsAndComprehensiveIncomeLoss</Role>
      <ShortName>Consolidated Statements of Operations and Comprehensive Income (Loss)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>100080 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/StatementConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>100090 - Statement - Consolidated Statements of Changes in Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_StatementConsolidatedStatementsOfChangesInStockholdersEquity</Role>
      <ShortName>Consolidated Statements of Changes in Stockholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>100100 - Statement - Consolidated Statement of Changes in Members' (Deficit) Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_StatementConsolidatedStatementOfChangesInMembersDeficitEquity</Role>
      <ShortName>Consolidated Statement of Changes in Members' (Deficit) Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>100110 - Disclosure - Organization, Nature of Business, and Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureOrganizationNatureOfBusinessAndBasisOfPresentation</Role>
      <ShortName>Organization, Nature of Business, and Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>100120 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>100130 - Disclosure - Acquisitions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureAcquisitions</Role>
      <ShortName>Acquisitions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>100150 - Disclosure - Property and Equipment, net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/DisclosurePropertyAndEquipmentNet1</Role>
      <ShortName>Property and Equipment, net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>100160 - Disclosure - Goodwill, Trade Name, and Customer Lists</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureGoodwillTradeNameAndCustomerLists</Role>
      <ShortName>Goodwill, Trade Name, and Customer Lists</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>100170 - Disclosure - Long-term Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureLongTermDebt</Role>
      <ShortName>Long-term Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>100180 - Disclosure - Derivatives</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureDerivatives</Role>
      <ShortName>Derivatives</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>100190 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>100200 - Disclosure - Revenues</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureRevenues</Role>
      <ShortName>Revenues</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>100210 - Disclosure - Share-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureShareBasedCompensation</Role>
      <ShortName>Share-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>100220 - Disclosure - Defined Contribution Plan</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/DisclosureDefinedContributionPlan</Role>
      <ShortName>Defined Contribution Plan</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>100230 - Disclosure - Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureEquity</Role>
      <ShortName>Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>100240 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>100250 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureRelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>100260 - Disclosure - Net Income (Loss) Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureNetIncomeLossPerShare</Role>
      <ShortName>Net Income (Loss) Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>100270 - Disclosure - Entity-Wide Disclosures</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureEntityWideDisclosures</Role>
      <ShortName>Entity-Wide Disclosures</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>100280 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureSubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>100290 - Disclosure - Condensed Financial Information of Registrant</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCondensedFinancialInformationOfRegistrant</Role>
      <ShortName>Condensed Financial Information of Registrant</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>100300 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>100310 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>100320 - Disclosure - Acquisitions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureAcquisitionsTables</Role>
      <ShortName>Acquisitions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureAcquisitions</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>100340 - Disclosure - Property and Equipment, net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/DisclosurePropertyAndEquipmentNetTables</Role>
      <ShortName>Property and Equipment, net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/DisclosurePropertyAndEquipmentNet1</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>100350 - Disclosure - Goodwill, Trade Name, and Customer Lists (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureGoodwillTradeNameAndCustomerListsTables</Role>
      <ShortName>Goodwill, Trade Name, and Customer Lists (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureGoodwillTradeNameAndCustomerLists</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>100360 - Disclosure - Long-term Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureLongTermDebtTables</Role>
      <ShortName>Long-term Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureLongTermDebt</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>100370 - Disclosure - Derivatives (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureDerivativesTables</Role>
      <ShortName>Derivatives (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureDerivatives</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>100380 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureIncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureIncomeTaxes</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>100390 - Disclosure - Revenues (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureRevenuesTables</Role>
      <ShortName>Revenues (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureRevenues</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>100400 - Disclosure - Share-based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureShareBasedCompensationTables</Role>
      <ShortName>Share-based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>100410 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>100420 - Disclosure - Net Income (Loss) Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureNetIncomeLossPerShareTables</Role>
      <ShortName>Net Income (Loss) Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureNetIncomeLossPerShare</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>100430 - Disclosure - Entity-Wide Disclosures (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureEntityWideDisclosuresTables</Role>
      <ShortName>Entity-Wide Disclosures (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureEntityWideDisclosures</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>100440 - Disclosure - Condensed Financial Information of Registrant (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCondensedFinancialInformationOfRegistrantTables</Role>
      <ShortName>Condensed Financial Information of Registrant (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCondensedFinancialInformationOfRegistrant</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>100450 - Disclosure - Organization, Nature of Business, and Basis of Presentation - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureOrganizationNatureOfBusinessAndBasisOfPresentationAdditionalInformationDetails</Role>
      <ShortName>Organization, Nature of Business, and Basis of Presentation - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>100460 - Disclosure - Summary of Significant Accounting Policies - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesScheduleOfFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>100470 - Disclosure - Summary of Significant Accounting Policies - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>100480 - Disclosure - Acquisitions - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureAcquisitionsAdditionalInformationDetails</Role>
      <ShortName>Acquisitions - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>100490 - Disclosure - Acquisitions - Summary of Consideration Paid and Amounts Recognized for Assets Acquired and Liabilities Assumed (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureAcquisitionsSummaryOfConsiderationPaidAndAmountsRecognizedForAssetsAcquiredAndLiabilitiesAssumedDetails</Role>
      <ShortName>Acquisitions - Summary of Consideration Paid and Amounts Recognized for Assets Acquired and Liabilities Assumed (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>100500 - Disclosure - Acquisitions - Summary of Business Acquisition Pro Forma Results (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureAcquisitionsSummaryOfBusinessAcquisitionProFormaResultsDetails</Role>
      <ShortName>Acquisitions - Summary of Business Acquisition Pro Forma Results (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>100510 - Disclosure - Property and Equipment, Net - Summary of Property and Equipment, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosurePropertyAndEquipmentNetSummaryOfPropertyAndEquipmentNetDetails</Role>
      <ShortName>Property and Equipment, Net - Summary of Property and Equipment, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>100520 - Disclosure - Property and Equipment, Net - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosurePropertyAndEquipmentNetAdditionalInformationDetails</Role>
      <ShortName>Property and Equipment, Net - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>100530 - Disclosure - Goodwill, Trade Name, and Customer Lists - Schedule of Changes in Carrying Amount of Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureGoodwillTradeNameAndCustomerListsScheduleOfChangesInCarryingAmountOfGoodwillDetails</Role>
      <ShortName>Goodwill, Trade Name, and Customer Lists - Schedule of Changes in Carrying Amount of Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>100540 - Disclosure - Goodwill, Trade Name, and Customer Lists - Summary of Gross Carrying Value and Accumulated Amortization of Finite-Lived Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureGoodwillTradeNameAndCustomerListsSummaryOfGrossCarryingValueAndAccumulatedAmortizationOfFiniteLivedIntangibleAssetsDetails</Role>
      <ShortName>Goodwill, Trade Name, and Customer Lists - Summary of Gross Carrying Value and Accumulated Amortization of Finite-Lived Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>100550 - Disclosure - Goodwill, Trade Name, and Customer Lists - Additional information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureGoodwillTradeNameAndCustomerListsAdditionalInformationDetails</Role>
      <ShortName>Goodwill, Trade Name, and Customer Lists - Additional information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>100560 - Disclosure - Goodwill, Trade Name, and Customer Lists - Schedule of Intangible Assets, Future Amortization Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureGoodwillTradeNameAndCustomerListsScheduleOfIntangibleAssetsFutureAmortizationExpenseDetails</Role>
      <ShortName>Goodwill, Trade Name, and Customer Lists - Schedule of Intangible Assets, Future Amortization Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>100570 - Disclosure - Long-term Debt - Fair Value of Company's Long-term Debt Obligations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/DisclosureLongtermDebtFairValueOfCompanysLongtermDebtObligationsDetails3</Role>
      <ShortName>Long-term Debt - Fair Value of Company's Long-term Debt Obligations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>100580 - Disclosure - Long-term Debt - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureLongTermDebtAdditionalInformationDetails</Role>
      <ShortName>Long-term Debt - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>100590 - Disclosure - Long-term Debt - Schedule of Future Maturities of Long-term Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureLongTermDebtScheduleOfFutureMaturitiesOfLongTermDebtDetails</Role>
      <ShortName>Long-term Debt - Schedule of Future Maturities of Long-term Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>100600 - Disclosure - Derivatives - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureDerivativesAdditionalInformationDetails</Role>
      <ShortName>Derivatives - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>100610 - Disclosure - Derivatives - Summary of Location and Fair Value of Financial Position and Location of Derivative Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/DisclosureDerivativesSummaryOfLocationAndFairValueOfFinancialPositionAndLocationOfDerivativeInstrumentsDetails</Role>
      <ShortName>Derivatives - Summary of Location and Fair Value of Financial Position and Location of Derivative Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>100620 - Disclosure - Income Taxes - Summary of (Loss) Income Before Income Tax Benefits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureIncomeTaxesSummaryOfLossIncomeBeforeIncomeTaxBenefitsDetails</Role>
      <ShortName>Income Taxes - Summary of (Loss) Income Before Income Tax Benefits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>100630 - Disclosure - Income Taxes - Summary of Current and Deferred Portions of Income Tax Benefits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureIncomeTaxesSummaryOfCurrentAndDeferredPortionsOfIncomeTaxBenefitsDetails</Role>
      <ShortName>Income Taxes - Summary of Current and Deferred Portions of Income Tax Benefits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>100640 - Disclosure - Income Taxes - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureIncomeTaxesAdditionalInformationDetails</Role>
      <ShortName>Income Taxes - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>100650 - Disclosure - Income Taxes - Summary of Reconciliation of U.S. Federal Statutory Income Tax Rate and Effective Income Tax Rate (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/DisclosureIncomeTaxesSummaryOfReconciliationOfUsFederalStatutoryIncomeTaxRateAndEffectiveIncomeTaxRateDetails</Role>
      <ShortName>Income Taxes - Summary of Reconciliation of U.S. Federal Statutory Income Tax Rate and Effective Income Tax Rate (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>100660 - Disclosure - Income Taxes - Summary of Net Deferred Tax Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureIncomeTaxesSummaryOfNetDeferredTaxAssetsDetails</Role>
      <ShortName>Income Taxes - Summary of Net Deferred Tax Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>100670 - Disclosure - Income Taxes - Summary of Operating Loss Carryforwards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureIncomeTaxesSummaryOfOperatingLossCarryforwardsDetails</Role>
      <ShortName>Income Taxes - Summary of Operating Loss Carryforwards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>100680 - Disclosure - Income Taxes - Summary of Income Tax Contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureIncomeTaxesSummaryOfIncomeTaxContingenciesDetails</Role>
      <ShortName>Income Taxes - Summary of Income Tax Contingencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>100690 - Disclosure - Revenues - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureRevenuesAdditionalInformationDetails</Role>
      <ShortName>Revenues - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>100700 - Disclosure - Revenues - Schedule of Revenues by Geographic Region (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureRevenuesScheduleOfRevenuesByGeographicRegionDetails</Role>
      <ShortName>Revenues - Schedule of Revenues by Geographic Region (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>100710 - Disclosure - Share-Based Compensation - Summary of Recognition of Share-Based Compensation related to Employees (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureShareBasedCompensationSummaryOfRecognitionOfShareBasedCompensationRelatedToEmployeesDetails</Role>
      <ShortName>Share-Based Compensation - Summary of Recognition of Share-Based Compensation related to Employees (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>100720 - Disclosure - Share-Based Compensation - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureShareBasedCompensationAdditionalInformationDetails</Role>
      <ShortName>Share-Based Compensation - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>100730 - Disclosure - Share-Based Compensation - Summary of Assumptions Applied to Establish Fair Value of Options Granted Using Black-Scholes Option Pricing Model (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureShareBasedCompensationSummaryOfAssumptionsAppliedToEstablishFairValueOfOptionsGrantedUsingBlackScholesOptionPricingModelDetails</Role>
      <ShortName>Share-Based Compensation - Summary of Assumptions Applied to Establish Fair Value of Options Granted Using Black-Scholes Option Pricing Model (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>100740 - Disclosure - Share-Based Compensation - Summary of the Profits Interest Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureShareBasedCompensationSummaryOfProfitsInterestActivityDetails</Role>
      <ShortName>Share-Based Compensation - Summary of the Profits Interest Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>100750 - Disclosure - Share-Based Compensation - Summary of the Option Unit Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureShareBasedCompensationSummaryOfOptionUnitActivityDetails</Role>
      <ShortName>Share-Based Compensation - Summary of the Option Unit Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>100760 - Disclosure - Share-Based Compensation - Summary of the RSU Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureShareBasedCompensationSummaryOfRSUActivityDetails</Role>
      <ShortName>Share-Based Compensation - Summary of the RSU Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>100770 - Disclosure - Defined Contribution Plan - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/DisclosureDefinedContributionPlanAdditionalInformationDetails</Role>
      <ShortName>Defined Contribution Plan - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>100780 - Disclosure - Equity - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureEquityAdditionalInformationDetails</Role>
      <ShortName>Equity - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>100790 - Disclosure - Commitments and Contingencies - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCommitmentsAndContingenciesAdditionalInformationDetails</Role>
      <ShortName>Commitments and Contingencies - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>100800 - Disclosure - Commitments and Contingencies - Amortization and Interest Expense Related to Capital Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCommitmentsAndContingenciesAmortizationAndInterestExpenseRelatedToCapitalLeasesDetails</Role>
      <ShortName>Commitments and Contingencies - Amortization and Interest Expense Related to Capital Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>100810 - Disclosure - Commitments and Contingencies - Schedule of Future Minimum Rental Payments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCommitmentsAndContingenciesScheduleOfFutureMinimumRentalPaymentsDetails</Role>
      <ShortName>Commitments and Contingencies - Schedule of Future Minimum Rental Payments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>100820 - Disclosure - Related Party Transactions - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureRelatedPartyTransactionsAdditionalInformationDetails</Role>
      <ShortName>Related Party Transactions - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>100830 - Disclosure - Net Income (Loss) Per Share - Summary of Basic and Diluted Net Income (Loss) Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/DisclosureNetIncomeLossPerShareSummaryOfBasicAndDilutedNetIncomeLossPerShareDetails</Role>
      <ShortName>Net Income (Loss) Per Share - Summary of Basic and Diluted Net Income (Loss) Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureNetIncomeLossPerShareTables</ParentRole>
      <Position>78</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>100840 - Disclosure - Net Income (Loss) Per Share (Additional Information) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/DisclosureNetIncomeLossPerShareAdditionalInformationDetails</Role>
      <ShortName>Net Income (Loss) Per Share (Additional Information) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureNetIncomeLossPerShareTables</ParentRole>
      <Position>79</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>100850 - Disclosure - Entity-Wide Disclosures - Summary of Long Lived Assets by Geographical Area (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureEntityWideDisclosuresSummaryOfLongLivedAssetsByGeographicalAreaDetails</Role>
      <ShortName>Entity-Wide Disclosures - Summary of Long Lived Assets by Geographical Area (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>100870 - Disclosure - Subsequent Events (Additional Information) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/DisclosureSubsequentEventsAdditionalInformationDetails</Role>
      <ShortName>Subsequent Events (Additional Information) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://fadv.com/20211231/taxonomy/role/Role_DisclosureSubsequentEvents</ParentRole>
      <Position>81</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>100880 - Disclosure - Condensed Financial Information of Registrant - Condensed Balance Sheets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCondensedFinancialInformationOfRegistrantCondensedBalanceSheetsDetails</Role>
      <ShortName>Condensed Financial Information of Registrant - Condensed Balance Sheets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>100890 - Disclosure - Condensed Financial Information of Registrant - Condensed Balance Sheets (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCondensedFinancialInformationOfRegistrantCondensedBalanceSheetsParentheticalDetails</Role>
      <ShortName>Condensed Financial Information of Registrant - Condensed Balance Sheets (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>100900 - Disclosure - Condensed Financial Information of Registrant - Condensed Statement Of Operations And Comprehensive (Loss) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCondensedFinancialInformationOfRegistrantCondensedStatementOfOperationsAndComprehensiveLossDetails</Role>
      <ShortName>Condensed Financial Information of Registrant - Condensed Statement Of Operations And Comprehensive (Loss) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="fa-20211231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>100910 - Disclosure - Condensed Financial Information of Registrant - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://fadv.com/20211231/taxonomy/role/Role_DisclosureCondensedFinancialInformationOfRegistrantAdditionalInformationDetails</Role>
      <ShortName>Condensed Financial Information of Registrant - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</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="fa-20211231.htm">fa-20211231.htm</File>
    <File>fa-20211231.xsd</File>
    <File>fa-20211231_cal.xml</File>
    <File>fa-20211231_def.xml</File>
    <File>fa-20211231_lab.xml</File>
    <File>fa-20211231_pre.xml</File>
    <File>fa-ex10_19.htm</File>
    <File>fa-ex21_1.htm</File>
    <File>fa-ex23_1.htm</File>
    <File>fa-ex31_1.htm</File>
    <File>fa-ex31_2.htm</File>
    <File>fa-ex32_1.htm</File>
    <File>fa-ex32_2.htm</File>
    <File>fa-ex4_1.htm</File>
  </InputFiles>
  <SupplementalFiles>
    <File>img3952526_0.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="1">http://fasb.org/srt/2021-01-31</BaseTaxonomy>
    <BaseTaxonomy items="1163">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>
