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v3.25.2

Beneficial Interests - Narrative (Details) - USD ($) $ in Millions | Jun. 30, 2025 | Dec. 31, 2024
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Line of Credit Receivable and Beneficial Interest Asset |  |
Schedule Of Beneficial Interest [Line Items] |  |
Cash held by institutional investor | $ 187.2 | $ 137.4

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- Definition Cash Held By Institutional Investor + References No definition available. + Details
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Namespace Prefix: | upst_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Schedule Of Beneficial Interest + References No definition available. + Details
Name: | upst_ScheduleOfBeneficialInterestLineItems
Namespace Prefix: | upst_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_FairValueByAssetClassAxis=upst_LineOfCreditReceivableAndBeneficialInterestAssetMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |