Beneficial Interests - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Schedule Of Beneficial Interest [Line Items]
Loans held in consolidated securitization	$ 118.5	$ 179.1
Variable Interest Entity, Not Primary Beneficiary \| Asset Pledged as Collateral
Schedule Of Beneficial Interest [Line Items]
Loans held in consolidated securitization	$ 18.9

Loans Held in Consolidated Securitization, Fair Value Disclosure

No definition available.

Name:	upst_LoansHeldInConsolidatedSecuritizationFairValueDisclosure
Namespace Prefix:	upst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant