Fair Value of Assets and Liabilities - Schedule of Credit Card Derivative Asset (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)
Servicing Assets And Liabilities Fair Value [Line Items]
Credit card derivative	$ 40,984	$ 38,739
Credit Card Derivative
Servicing Assets And Liabilities Fair Value [Line Items]
Credit card derivative	40,984	38,739
Outstanding Credit Card Principal Balance, Prosper and Coastal Allocations	$ 303,535	$ 303,245
Credit Card Derivative \| Discount rate on Prosper Allocations
Servicing Assets And Liabilities Fair Value [Line Items]
Valuation techniques	0.2244	0.2244
Credit Card Derivative \| Discount rate on Coastal Program Fee
Servicing Assets And Liabilities Fair Value [Line Items]
Valuation techniques	0.2244	0.2244
Credit Card Derivative \| Prepayment rate
Servicing Assets And Liabilities Fair Value [Line Items]
Valuation techniques	0.0818	0.0814
Credit Card Derivative \| Prepayment rate \| Applying a 1.1 multiplier to prepayment rate
Servicing Assets And Liabilities Fair Value [Line Items]
Expected fair value with change in assumptions	$ 40,411	$ 38,210
Prepayment rate increase	1.10%
Credit Card Derivative \| Prepayment rate \| Applying a 0.9 multiplier to prepayment rate
Servicing Assets And Liabilities Fair Value [Line Items]
Expected fair value with change in assumptions	$ 41,566	$ 39,275
Prepayment rate decrease	0.90%
Credit Card Derivative \| Default rate
Servicing Assets And Liabilities Fair Value [Line Items]
Valuation techniques	0.1539	0.1565
Credit Card Derivative \| Default rate \| Applying a 1.1 multiplier to default rate
Servicing Assets And Liabilities Fair Value [Line Items]
Expected fair value with change in assumptions	$ 31,709	$ 29,252
Default rate increase	1.10%
Credit Card Derivative \| Default rate \| Applying a 0.9 multiplier to default rate
Servicing Assets And Liabilities Fair Value [Line Items]
Expected fair value with change in assumptions	$ 50,577	48,556
Default rate decrease	0.90%
Credit Card Derivative \| Discount rate \| 100 basis point increase in both discount rates
Servicing Assets And Liabilities Fair Value [Line Items]
Expected fair value with change in assumptions	$ 40,429	38,225
Discount rates increase	0.0100
Credit Card Derivative \| Discount rate \| 200 basis point increase in both discount rates
Servicing Assets And Liabilities Fair Value [Line Items]
Expected fair value with change in assumptions	$ 39,890	37,725
Discount rates increase	0.0200
Credit Card Derivative \| Discount rate \| 100 basis point decrease in both discount rates
Servicing Assets And Liabilities Fair Value [Line Items]
Expected fair value with change in assumptions	$ 41,556	39,269
Discount rates increase	0.0100
Credit Card Derivative \| Discount rate \| 200 basis point decrease in both discount rates
Servicing Assets And Liabilities Fair Value [Line Items]
Expected fair value with change in assumptions	$ 42,145	39,814
Discount rates increase	0.0200
Credit Card Servicing Obligation Liability
Servicing Assets And Liabilities Fair Value [Line Items]
Derivative liability	$ 8,576	$ 8,947
Credit Card Servicing Obligation Liability \| Discount rate on Prosper Allocations
Servicing Assets And Liabilities Fair Value [Line Items]
Derivative liability, measurement input	0.2244	0.2244
Credit Card Servicing Obligation Liability \| Prepayment rate
Servicing Assets And Liabilities Fair Value [Line Items]
Derivative liability, measurement input	0.0818	0.0814
Credit Card Servicing Obligation Liability \| Prepayment rate \| Applying a 1.1 multiplier to prepayment rate
Servicing Assets And Liabilities Fair Value [Line Items]
Derivative liability, expected fair value with change in assumptions	$ 8,481	$ 8,849
Prepayment rate increase	110.00%
Credit Card Servicing Obligation Liability \| Prepayment rate \| Applying a 0.9 multiplier to prepayment rate
Servicing Assets And Liabilities Fair Value [Line Items]
Derivative liability, expected fair value with change in assumptions	$ 8,672	$ 9,047
Prepayment rate decrease	90.00%
Credit Card Servicing Obligation Liability \| Default rate
Servicing Assets And Liabilities Fair Value [Line Items]
Derivative liability, measurement input	0.1539	0.1565
Credit Card Servicing Obligation Liability \| Default rate \| Applying a 1.1 multiplier to default rate
Servicing Assets And Liabilities Fair Value [Line Items]
Derivative liability, expected fair value with change in assumptions	$ 8,371	$ 8,730
Default rate increase	110.00%
Credit Card Servicing Obligation Liability \| Default rate \| Applying a 0.9 multiplier to default rate
Servicing Assets And Liabilities Fair Value [Line Items]
Derivative liability, expected fair value with change in assumptions	$ 8,786	$ 9,170
Default rate decrease	90.00%
Credit Card Servicing Obligation Liability \| Market servicing rate
Servicing Assets And Liabilities Fair Value [Line Items]
Derivative liability, measurement input	0.0200	0.0200
Credit Card Servicing Obligation Liability \| Discount rate \| Market servicing rate increase of 0.10%
Servicing Assets And Liabilities Fair Value [Line Items]
Servicing rate increase	0.10%
Derivative liability, expected fair value with change in assumptions	$ 9,025	$ 9,415
Credit Card Servicing Obligation Liability \| Discount rate \| Market servicing rate decrease of 0.10%
Servicing Assets And Liabilities Fair Value [Line Items]
Servicing rate decrease	0.10%
Derivative liability, expected fair value with change in assumptions	$ 8,128	$ 8,481

PROSPER MARKETPLACE, INC 10-Q