Borrowings (Details)					9 Months Ended	12 Months Ended
	Oct. 28, 2021 USD ($)	Sep. 08, 2021 USD ($)	May 10, 2021 USD ($)	Mar. 08, 2021 USD ($) class	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jul. 08, 2021 USD ($)	Mar. 24, 2021 USD ($)	Feb. 18, 2021 USD ($)
Debt Instrument [Line Items]
Current Balance					$ 525,471,000	$ 246,385,000
Initial collateral balance					9,300,000
Current balance					1,162,948,000	1,167,309,000
Credit Facility | Warehouse Facility
Debt Instrument [Line Items]
Current Balance					525,471,000	246,385,000
Commitment Amount					$ 600,000,000	$ 400,000,000
Repayments of facility		$ 219,000,000
Credit Facility | Warehouse Facility | LIBOR
Debt Instrument [Line Items]
Interest Rate, basis spread minimum					0.00%	0.00%
Interest Rate, basis spread					2.17%	2.45%
Credit Facility | New Warehouse Facility
Debt Instrument [Line Items]
Commitment Amount		$ 600,000,000
Interest Rate, basis spread		2.17%
Asset-Backed Notes
Debt Instrument [Line Items]
Initial note amount issued					$ 1,154,412,000	$ 1,154,419,000
Current balance					1,162,948,000	1,167,309,000
Asset-Backed Notes | Initial Collateral
Debt Instrument [Line Items]
Initial collateral balance					1,190,509,000	1,226,888,000
Asset-Backed Notes | Current Collateral
Debt Instrument [Line Items]
Initial collateral balance					1,216,204,000	1,248,996,000
Asset-Backed Notes | Oportun Issuance Trust (Series 2021-B)
Debt Instrument [Line Items]
Initial note amount issued			$ 500,000,000		500,000,000
Current balance					$ 501,743,000
Weighted average interest rate			2.05%		2.05%
Original revolving period			3 years		3 years
Number of debt classes | class				4
Asset-Backed Notes | Oportun Issuance Trust (Series 2021-B) | Initial Collateral
Debt Instrument [Line Items]
Initial collateral balance					$ 512,759,000
Asset-Backed Notes | Oportun Issuance Trust (Series 2021-B) | Current Collateral
Debt Instrument [Line Items]
Initial collateral balance					523,870,000
Asset-Backed Notes | Oportun Funding XIV, LLC (Series 2021-A)
Debt Instrument [Line Items]
Initial note amount issued				$ 375,000,000	375,000,000
Current balance					$ 377,120,000
Weighted average interest rate				1.79%	1.79%
Original revolving period				2 years	2 years
Number of debt classes | class				4
Asset-Backed Notes | Oportun Funding XIV, LLC (Series 2021-A) | Initial Collateral
Debt Instrument [Line Items]
Initial collateral balance					$ 383,632,000
Asset-Backed Notes | Oportun Funding XIV, LLC (Series 2021-A) | Current Collateral
Debt Instrument [Line Items]
Initial collateral balance					392,332,000
Asset-Backed Notes | Oportun Funding XIII, LLC (Series 2019-A)
Debt Instrument [Line Items]
Initial note amount issued					279,412,000	279,412,000
Current balance					$ 284,085,000	$ 283,299,000
Weighted average interest rate					3.46%	3.46%
Original revolving period					3 years	3 years
Asset-Backed Notes | Oportun Funding XIII, LLC (Series 2019-A) | Initial Collateral
Debt Instrument [Line Items]
Initial collateral balance					$ 294,118,000	$ 294,118,000
Asset-Backed Notes | Oportun Funding XIII, LLC (Series 2019-A) | Current Collateral
Debt Instrument [Line Items]
Initial collateral balance					$ 300,002,000	299,237,000
Asset-Backed Notes | Oportun Funding XII, LLC (Series 2018-D)
Debt Instrument [Line Items]
Initial note amount issued		$ 175,000,000				175,002,000
Current balance						$ 178,182,000
Weighted average interest rate						4.50%
Original revolving period						3 years
Asset-Backed Notes | Oportun Funding XII, LLC (Series 2018-D) | Initial Collateral
Debt Instrument [Line Items]
Initial collateral balance						$ 184,213,000
Asset-Backed Notes | Oportun Funding XII, LLC (Series 2018-D) | Current Collateral
Debt Instrument [Line Items]
Initial collateral balance						187,570,000
Asset-Backed Notes | Oportun Funding X, LLC (Series 2018-C)
Debt Instrument [Line Items]
Initial note amount issued						275,000,000	$ 275,000,000
Current balance						$ 279,171,000
Weighted average interest rate						4.39%
Original revolving period						3 years
Asset-Backed Notes | Oportun Funding X, LLC (Series 2018-C) | Initial Collateral
Debt Instrument [Line Items]
Initial collateral balance						$ 289,474,000
Asset-Backed Notes | Oportun Funding X, LLC (Series 2018-C) | Current Collateral
Debt Instrument [Line Items]
Initial collateral balance						294,710,000
Asset-Backed Notes | Oportun Funding IX, LLC (Series 2018-B)
Debt Instrument [Line Items]
Initial note amount issued						225,001,000		$ 225,000,000
Current balance						$ 226,653,000
Weighted average interest rate						4.18%
Original revolving period						3 years
Asset-Backed Notes | Oportun Funding IX, LLC (Series 2018-B) | Initial Collateral
Debt Instrument [Line Items]
Initial collateral balance						$ 236,854,000
Asset-Backed Notes | Oportun Funding IX, LLC (Series 2018-B) | Current Collateral
Debt Instrument [Line Items]
Initial collateral balance						241,237,000
Asset-Backed Notes | Oportun Funding VIII, LLC (Series 2018-A)
Debt Instrument [Line Items]
Initial note amount issued						200,004,000			$ 200,000,000
Current balance						$ 200,004,000
Weighted average interest rate						3.83%
Original revolving period						3 years
Asset-Backed Notes | Oportun Funding VIII, LLC (Series 2018-A) | Initial Collateral
Debt Instrument [Line Items]
Initial collateral balance						$ 222,229,000
Asset-Backed Notes | Oportun Funding VIII, LLC (Series 2018-A) | Current Collateral
Debt Instrument [Line Items]
Initial collateral balance						$ 226,242,000
Asset-Backed Notes | Oportun Issuance Trust (Series 2021-C) | Subsequent Event
Debt Instrument [Line Items]
Initial note amount issued	$ 500,000,000
Weighted average interest rate	2.48%
Original revolving period	3 years