Fair Value of Assets and Liabilities - Sensitivity of Fair Value of Loans Invested in by the Company, Asset-backed Securities Related to Structured Program Transactions and Servicing Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale at fair value	$ 142,370	$ 121,902
Servicing assets	67,726	56,347
Level 3 Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale at fair value	142,370	121,902
Servicing assets	67,726	56,347
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing assets	67,726	56,347	$ 89,680
Fair Value, Measurements, Recurring | Level 3 Inputs | Servicing Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing assets	67,726	56,347
Discount rates, impact of 100 basis point increase	(558)	(455)
Discount rates, impact of 200 basis point increase	(1,115)	(911)
Expected credit loss on rates on underlying loans, 10% adverse change	(693)	(346)
Expected credit loss on rates on underlying loans, 20% adverse change	(1,386)	(691)
Expected prepayment rates, 10% adverse change	(2,401)	(1,596)
Expected prepayment rates, 20% adverse change	(4,802)	(3,192)
Loans held for sale at fair value | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held for sale at fair value	142,370	121,902
Discount rates, impact of 100 basis point increase	(1,540)	(1,151)
Discount rates, impact of 200 basis point increase	(3,055)	(2,282)
Expected credit loss rates on underlying loans, 10% adverse change	(608)	(1,099)
Expected credit loss rates on underlying loans, 20% adverse change	(1,236)	(2,220)
Expected prepayment rates, 10% adverse change	(1,450)	(273)
Expected prepayment rates, 20% adverse change	$ (2,997)	$ (556)
Loans held for sale at fair value | Fair Value, Measurements, Recurring | Expected weighted-average life (in years)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Expected weighted-average life (in years)	1 year 3 months 18 days	1 year 1 month 6 days