<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.26.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>371</ContextCount>
  <ElementCount>427</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>101</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>6</UnitCount>
  <MyReports>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0000001 - Document - Cover</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/Cover</Role>
      <ShortName>Cover</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>9952151 - Statement - Condensed Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/CondensedConsolidatedBalanceSheets</Role>
      <ShortName>Condensed Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>9952152 - Statement - Condensed Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/CondensedConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Condensed Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>9952153 - Statement - Condensed Consolidated Statements of Operations and Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/CondensedConsolidatedStatementsofOperationsandComprehensiveLoss</Role>
      <ShortName>Condensed Consolidated Statements of Operations and Comprehensive Loss</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>9952154 - Statement - Condensed Consolidated Statements of Stockholders??? Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/CondensedConsolidatedStatementsofStockholdersEquity</Role>
      <ShortName>Condensed Consolidated Statements of Stockholders??? Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>9952155 - Statement - Condensed Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/CondensedConsolidatedStatementsofCashFlows</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>9952156 - Statement - Condensed Consolidated Statements of Cash Flows (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/CondensedConsolidatedStatementsofCashFlowsParenthetical</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>9952157 - Disclosure - Description of Business and Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/DescriptionofBusinessandSignificantAccountingPolicies</Role>
      <ShortName>Description of Business and Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>9952158 - Disclosure - Revenue</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/Revenue</Role>
      <ShortName>Revenue</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>9952159 - Disclosure - Variable Interest Entities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/VariableInterestEntities</Role>
      <ShortName>Variable Interest Entities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>9952160 - Disclosure - Beneficial Interests</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BeneficialInterests</Role>
      <ShortName>Beneficial Interests</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>9952161 - Disclosure - Fair Value Measurement</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurement</Role>
      <ShortName>Fair Value Measurement</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>9952162 - Disclosure - Goodwill and Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/GoodwillandIntangibleAssets</Role>
      <ShortName>Goodwill and Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>9952163 - Disclosure - Balance Sheet Components</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BalanceSheetComponents</Role>
      <ShortName>Balance Sheet Components</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>9952164 - Disclosure - Borrowings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/Borrowings</Role>
      <ShortName>Borrowings</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>9952165 - Disclosure - Stockholders??? Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/StockholdersEquity</Role>
      <ShortName>Stockholders??? Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>9952166 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/Leases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>9952167 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/CommitmentsandContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>9952168 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>9952169 - Disclosure - Net Income (Loss) Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/NetIncomeLossPerShare</Role>
      <ShortName>Net Income (Loss) Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>9952170 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/SegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>9952171 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/SubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>9955511 - Disclosure - Description of Business and Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/DescriptionofBusinessandSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Description of Business and Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/DescriptionofBusinessandSignificantAccountingPolicies</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>9955512 - Disclosure - Revenue (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/RevenueTables</Role>
      <ShortName>Revenue (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/Revenue</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>9955513 - Disclosure - Variable Interest Entities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/VariableInterestEntitiesTables</Role>
      <ShortName>Variable Interest Entities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/VariableInterestEntities</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>9955514 - Disclosure - Beneficial Interests (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BeneficialInterestsTables</Role>
      <ShortName>Beneficial Interests (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/BeneficialInterests</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>9955515 - Disclosure - Fair Value Measurement (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementTables</Role>
      <ShortName>Fair Value Measurement (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/FairValueMeasurement</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>9955516 - Disclosure - Goodwill and Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/GoodwillandIntangibleAssetsTables</Role>
      <ShortName>Goodwill and Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/GoodwillandIntangibleAssets</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>9955517 - Disclosure - Balance Sheet Components (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BalanceSheetComponentsTables</Role>
      <ShortName>Balance Sheet Components (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/BalanceSheetComponents</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>9955518 - Disclosure - Borrowings (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BorrowingsTables</Role>
      <ShortName>Borrowings (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/Borrowings</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>9955519 - Disclosure - Stockholders??? Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/StockholdersEquityTables</Role>
      <ShortName>Stockholders??? Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/StockholdersEquity</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>9955520 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/LeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/Leases</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>9955521 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/IncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/IncomeTaxes</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>9955522 - Disclosure - Net Income (Loss) Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/NetIncomeLossPerShareTables</Role>
      <ShortName>Net Income (Loss) Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/NetIncomeLossPerShare</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>9955523 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/SegmentInformationTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/SegmentInformation</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>9955524 - Disclosure - Revenue - Schedule of Disaggregation of Revenue by Type of Service (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/RevenueScheduleofDisaggregationofRevenuebyTypeofServiceDetails</Role>
      <ShortName>Revenue - Schedule of Disaggregation of Revenue by Type of Service (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>9955525 - Disclosure - Revenue - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/RevenueNarrativeDetails</Role>
      <ShortName>Revenue - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>9955526 - Disclosure - Revenue - Schedule of Customers Accounting for Greater Than 10% of Revenue and Accounts Receivable (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/RevenueScheduleofCustomersAccountingforGreaterThan10ofRevenueandAccountsReceivableDetails</Role>
      <ShortName>Revenue - Schedule of Customers Accounting for Greater Than 10% of Revenue and Accounts Receivable (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>9955527 - Disclosure - Revenue - Schedule of Collection Agency and Borrower Fees (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/RevenueScheduleofCollectionAgencyandBorrowerFeesDetails</Role>
      <ShortName>Revenue - Schedule of Collection Agency and Borrower Fees (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>9955528 - Disclosure - Revenue - Schedule of Components of Interest Income and Fair Value Adjustments, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/RevenueScheduleofComponentsofInterestIncomeandFairValueAdjustmentsNetDetails</Role>
      <ShortName>Revenue - Schedule of Components of Interest Income and Fair Value Adjustments, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>9955529 - Disclosure - Variable Interest Entities - Schedule of Financial Assets and Liabilities from Variable Interest Entities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/VariableInterestEntitiesScheduleofFinancialAssetsandLiabilitiesfromVariableInterestEntitiesDetails</Role>
      <ShortName>Variable Interest Entities - Schedule of Financial Assets and Liabilities from Variable Interest Entities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>9955530 - Disclosure - Variable Interest Entities - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/VariableInterestEntitiesNarrativeDetails</Role>
      <ShortName>Variable Interest Entities - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>9955531 - Disclosure - Beneficial Interests - Schedule of Beneficial Interest Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BeneficialInterestsScheduleofBeneficialInterestAssetsandLiabilitiesDetails</Role>
      <ShortName>Beneficial Interests - Schedule of Beneficial Interest Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>9955532 - Disclosure - Beneficial Interests - Schedule of Maximum Exposure to Losses by Asset Type (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BeneficialInterestsScheduleofMaximumExposuretoLossesbyAssetTypeDetails</Role>
      <ShortName>Beneficial Interests - Schedule of Maximum Exposure to Losses by Asset Type (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>9955533 - Disclosure - Fair Value Measurement - Schedule of Assets and Liabilities Measured at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementScheduleofAssetsandLiabilitiesMeasuredatFairValueDetails</Role>
      <ShortName>Fair Value Measurement - Schedule of Assets and Liabilities Measured at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>9955534 - Disclosure - Fair Value Measurement - Schedule of Fair Value of Classes of Loans Held by the Company (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementScheduleofFairValueofClassesofLoansHeldbytheCompanyDetails</Role>
      <ShortName>Fair Value Measurement - Schedule of Fair Value of Classes of Loans Held by the Company (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>9955535 - Disclosure - Fair Value Measurement - Schedule of Significant Unobservable Inputs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementScheduleofSignificantUnobservableInputsDetails</Role>
      <ShortName>Fair Value Measurement - Schedule of Significant Unobservable Inputs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>9955536 - Disclosure - Fair Value Measurement - Schedule of Sensitivity Analysis of Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementScheduleofSensitivityAnalysisofFairValueDetails</Role>
      <ShortName>Fair Value Measurement - Schedule of Sensitivity Analysis of Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>9955537 - Disclosure - Fair Value Measurement - Schedule of Rollforward of Level 3 Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementScheduleofRollforwardofLevel3AssetsDetails</Role>
      <ShortName>Fair Value Measurement - Schedule of Rollforward of Level 3 Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>9955538 - Disclosure - Fair Value Measurement - Schedule of Aggregate Fair Value and Principal Outstanding of All Loans And Loans 90 Days or More Past Due (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementScheduleofAggregateFairValueandPrincipalOutstandingofAllLoansAndLoans90DaysorMorePastDueDetails</Role>
      <ShortName>Fair Value Measurement - Schedule of Aggregate Fair Value and Principal Outstanding of All Loans And Loans 90 Days or More Past Due (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>9955539 - Disclosure - Fair Value Measurement - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementNarrativeDetails</Role>
      <ShortName>Fair Value Measurement - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>9955540 - Disclosure - Fair Value Measurement - Schedule of Level Three Assets and Liabilities Rollforward (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementScheduleofLevelThreeAssetsandLiabilitiesRollforwardDetails</Role>
      <ShortName>Fair Value Measurement - Schedule of Level Three Assets and Liabilities Rollforward (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>9955541 - Disclosure - Fair Value Measurement - Schedule of Level 3 Fair Value Assumptions for Loan Servicing Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementScheduleofLevel3FairValueAssumptionsforLoanServicingAssetsandLiabilitiesDetails</Role>
      <ShortName>Fair Value Measurement - Schedule of Level 3 Fair Value Assumptions for Loan Servicing Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>9955542 - Disclosure - Fair Value Measurement - Schedule of Fair Value Sensitivity of Loan Servicing Assets and Liabilities to Adverse Changes in Key Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementScheduleofFairValueSensitivityofLoanServicingAssetsandLiabilitiestoAdverseChangesinKeyAssumptionsDetails</Role>
      <ShortName>Fair Value Measurement - Schedule of Fair Value Sensitivity of Loan Servicing Assets and Liabilities to Adverse Changes in Key Assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>9955543 - Disclosure - Fair Value Measurement - Schedule of Servicing Liabilities at Fair Value Rollforward (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/FairValueMeasurementScheduleofServicingLiabilitiesatFairValueRollforwardDetails</Role>
      <ShortName>Fair Value Measurement - Schedule of Servicing Liabilities at Fair Value Rollforward (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>9955544 - Disclosure - Goodwill and Intangible Assets - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/GoodwillandIntangibleAssetsNarrativeDetails</Role>
      <ShortName>Goodwill and Intangible Assets - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>9955545 - Disclosure - Goodwill and Intangible Assets - Schedule of Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/GoodwillandIntangibleAssetsScheduleofIntangibleAssetsDetails</Role>
      <ShortName>Goodwill and Intangible Assets - Schedule of Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>9955546 - Disclosure - Goodwill and Intangible Assets - Schedule of Expected Future Amortization Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/GoodwillandIntangibleAssetsScheduleofExpectedFutureAmortizationExpenseDetails</Role>
      <ShortName>Goodwill and Intangible Assets - Schedule of Expected Future Amortization Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>9955547 - Disclosure - Balance Sheet Components - Schedule of Other Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BalanceSheetComponentsScheduleofOtherAssetsDetails</Role>
      <ShortName>Balance Sheet Components - Schedule of Other Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>9955548 - Disclosure - Balance Sheet Components - Schedule of Property, Equipment, and Software (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BalanceSheetComponentsScheduleofPropertyEquipmentandSoftwareDetails</Role>
      <ShortName>Balance Sheet Components - Schedule of Property, Equipment, and Software (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>9955549 - Disclosure - Balance Sheet Components - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BalanceSheetComponentsNarrativeDetails</Role>
      <ShortName>Balance Sheet Components - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>9955550 - Disclosure - Balance Sheet Components - Schedule of Accrued Expenses and Other Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BalanceSheetComponentsScheduleofAccruedExpensesandOtherLiabilitiesDetails</Role>
      <ShortName>Balance Sheet Components - Schedule of Accrued Expenses and Other Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>9955551 - Disclosure - Borrowings - Schedule of Aggregate Principal Outstanding of all Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BorrowingsScheduleofAggregatePrincipalOutstandingofallLoansDetails</Role>
      <ShortName>Borrowings - Schedule of Aggregate Principal Outstanding of all Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>9955552 - Disclosure - Borrowings - Schedule of Maturities of All Borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BorrowingsScheduleofMaturitiesofAllBorrowingsDetails</Role>
      <ShortName>Borrowings - Schedule of Maturities of All Borrowings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>9955553 - Disclosure - Borrowings - Schedule of Warehouse Credit Facilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BorrowingsScheduleofWarehouseCreditFacilitiesDetails</Role>
      <ShortName>Borrowings - Schedule of Warehouse Credit Facilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>9955554 - Disclosure - Borrowings - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BorrowingsNarrativeDetails</Role>
      <ShortName>Borrowings - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>9955555 - Disclosure - Borrowings - Schedule of Convertible Senior Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.upstartholdings.com/role/BorrowingsScheduleofConvertibleSeniorNotesDetails</Role>
      <ShortName>Borrowings - Schedule of Convertible Senior Notes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>9955556 - Disclosure - Borrowings - Schedule of Capped Call Transactions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/BorrowingsScheduleofCappedCallTransactionsDetails</Role>
      <ShortName>Borrowings - Schedule of Capped Call Transactions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>9955557 - Disclosure - Stockholders??? Equity - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/StockholdersEquityNarrativeDetails</Role>
      <ShortName>Stockholders??? Equity - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>9955558 - Disclosure - Stockholders??? Equity - Schedule of Reserved Shares of Common Stock for Issuance (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/StockholdersEquityScheduleofReservedSharesofCommonStockforIssuanceDetails</Role>
      <ShortName>Stockholders??? Equity - Schedule of Reserved Shares of Common Stock for Issuance (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>9955559 - Disclosure - Stockholders??? Equity - Schedule of Stock Option Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/StockholdersEquityScheduleofStockOptionActivityDetails</Role>
      <ShortName>Stockholders??? Equity - Schedule of Stock Option Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>9955560 - Disclosure - Stockholders??? Equity - Schedule of RSU and PRSU Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/StockholdersEquityScheduleofRSUandPRSUActivityDetails</Role>
      <ShortName>Stockholders??? Equity - Schedule of RSU and PRSU Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>9955561 - Disclosure - Stockholders??? Equity - Schedule of Weighted-Average Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/StockholdersEquityScheduleofWeightedAverageAssumptionsDetails</Role>
      <ShortName>Stockholders??? Equity - Schedule of Weighted-Average Assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>9955562 - Disclosure - Stockholders??? Equity - Schedule of Stock-based Compensation Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/StockholdersEquityScheduleofStockbasedCompensationExpenseDetails</Role>
      <ShortName>Stockholders??? Equity - Schedule of Stock-based Compensation Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>9955563 - Disclosure - Leases - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/LeasesNarrativeDetails</Role>
      <ShortName>Leases - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>9955564 - Disclosure - Leases - Schedule of Future Minimum Lease Payments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/LeasesScheduleofFutureMinimumLeasePaymentsDetails</Role>
      <ShortName>Leases - Schedule of Future Minimum Lease Payments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>9955565 - Disclosure - Leases - Schedule of Operating Lease Expense and Supplemental Cash and Non-cash Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/LeasesScheduleofOperatingLeaseExpenseandSupplementalCashandNoncashInformationDetails</Role>
      <ShortName>Leases - Schedule of Operating Lease Expense and Supplemental Cash and Non-cash Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>9955566 - Disclosure - Commitments and Contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/CommitmentsandContingenciesDetails</Role>
      <ShortName>Commitments and Contingencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/CommitmentsandContingencies</ParentRole>
      <Position>79</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>9955567 - Disclosure - Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/IncomeTaxesDetails</Role>
      <ShortName>Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/IncomeTaxesTables</ParentRole>
      <Position>80</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>9955568 - Disclosure - Net Income (Loss) Per Share - Schedule of Net Loss Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/NetIncomeLossPerShareScheduleofNetLossPerShareDetails</Role>
      <ShortName>Net Income (Loss) Per Share - Schedule of Net Loss Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/NetIncomeLossPerShareTables</ParentRole>
      <Position>81</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>9955569 - Disclosure - Net Income (Loss) Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/NetIncomeLossPerShareScheduleofAntidilutiveSecuritiesExcludedfromComputationofEarningsPerShareDetails</Role>
      <ShortName>Net Income (Loss) Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.upstartholdings.com/role/NetIncomeLossPerShareTables</ParentRole>
      <Position>82</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>9955570 - Disclosure - Segment Information - Schedule of Contribution Profit for the Company's Unsecured Lending Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/SegmentInformationScheduleofContributionProfitfortheCompanysUnsecuredLendingSegmentDetails</Role>
      <ShortName>Segment Information - Schedule of Contribution Profit for the Company's Unsecured Lending Segment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="upst-20260331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>9955571 - Disclosure - Segment Information - Schedule of Reconciliation of Total Contribution Profit to Net Loss Before Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.upstartholdings.com/role/SegmentInformationScheduleofReconciliationofTotalContributionProfittoNetLossBeforeIncomeTaxesDetails</Role>
      <ShortName>Segment Information - Schedule of Reconciliation of Total Contribution Profit to Net Loss Before Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" isDefinitelyFs="true" isUsgaap="true" original="upst-20260331.htm">upst-20260331.htm</File>
    <File>upst-20260331.xsd</File>
    <File>upst-20260331_cal.xml</File>
    <File>upst-20260331_def.xml</File>
    <File>upst-20260331_lab.xml</File>
    <File>upst-20260331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles>
    <File>upst-20260331_g1.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="1">http://fasb.org/srt/2025</BaseTaxonomy>
    <BaseTaxonomy items="878">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="30">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="9">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
