Fair Value Measurement - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans on non-accrual status	120 days
Charges-off loans	120 days
Notes receivable and residual certificates	$ 5,000
Average effect of fair value of hypothetical 20% adverse change in expected credit loss rates	(34.00%)
Upstart-powered personal loans
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Changes in fair value recorded in earnings	$ (17,000)
Fair Value, Inputs, Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held-for-sale	839,500		$ 882,800
Loans held-for-investment	142,700		127,600
Notes receivable and residual certificates	$ 5,009		$ 6,181
Fair Value, Inputs, Level 3 | Notes Receivable
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Average effect on fair value of a 100 basis point increase in discount rates	1.03%		1.10%
Average effect on fair value of a 200 basis point increase in discount rates	2.05%		2.18%
Fair Value, Inputs, Level 3 | Loans (at fair value)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Changes in fair value recorded in earnings	$ (48,161)	$ (19,511)
Fair Value, Inputs, Level 3 | Minimum | Discount rate | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trailing fees liability, measurement input	6.36%
Fair Value, Inputs, Level 3 | Minimum | Discount rate | Notes Receivable | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan receivable, measurement input	8.98%		8.42%
Fair Value, Inputs, Level 3 | Minimum | Discount rate | Loans (at fair value) | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan receivable, measurement input	6.36%		6.36%
Fair Value, Inputs, Level 3 | Minimum | Credit risk rate | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trailing fees liability, measurement input	0.01%
Fair Value, Inputs, Level 3 | Minimum | Credit risk rate | Notes Receivable | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan receivable, measurement input	0.59%		0.59%
Fair Value, Inputs, Level 3 | Minimum | Credit risk rate | Loans (at fair value) | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan receivable, measurement input	0.01%		0.01%
Fair Value, Inputs, Level 3 | Maximum | Discount rate | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trailing fees liability, measurement input	22.67%
Fair Value, Inputs, Level 3 | Maximum | Discount rate | Notes Receivable | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan receivable, measurement input	22.66%		22.27%
Fair Value, Inputs, Level 3 | Maximum | Discount rate | Loans (at fair value) | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan receivable, measurement input	22.67%		22.28%
Fair Value, Inputs, Level 3 | Maximum | Credit risk rate | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trailing fees liability, measurement input	93.05%
Fair Value, Inputs, Level 3 | Maximum | Credit risk rate | Notes Receivable | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan receivable, measurement input	50.69%		50.69%
Fair Value, Inputs, Level 3 | Maximum | Credit risk rate | Loans (at fair value) | Valuation Technique, Discounted Cash Flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loan receivable, measurement input	93.05%		93.09%