Fair Value of Financial Instruments - Valuation for Level 3 Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 1,054,335	$ 17,777,280
Total gains (realized/unrealized)
Included in earnings		103,782
Paydowns		(236,860)
Sales		(16,589,867)
Recovery of charge-off	0	35	$ (3,257)
Balance at the end of period		1,054,335	17,777,280
VIE, Primary Beneficiary
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		17,777,280	11,022,248
Total gains (realized/unrealized)
Included in earnings	(54,154)		443,823
Purchases			7,309,459
Paydowns			(994,993)
Recovery of charge-off			(3,257)
Balance at the end of period	839,419		17,777,280
VIE, Primary Beneficiary | Consolidated K-Series
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	0	16,724,451	11,022,248
Total gains (realized/unrealized)
Included in earnings		35,018	443,796
Purchases			6,253,739
Paydowns		(147,376)	(992,075)
Sales		(16,612,093)
Recovery of charge-off		35	(3,257)
Balance at the end of period		0	16,724,451
VIE, Primary Beneficiary | Consolidated SLST
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	1,054,335	1,052,829	0
Total gains (realized/unrealized)
Included in earnings		68,764	27
Purchases			1,055,720
Paydowns	(160,762)	(89,484)	(2,918)
Sales		22,226
Recovery of charge-off	$ 0	0	0
Balance at the end of period		$ 1,054,335	$ 1,052,829