Asset-Backed Securities Issued - Components of Asset-Backed Securities Issued by Consolidated Securitization Entities Sponsored, Along With Other Selected Information (Details)	Sep. 30, 2021 USD ($) series	Dec. 31, 2020 USD ($) series
Debt Instrument [Line Items]
Certificates	$ 1,510,056,000
Net Carrying Value	1,499,577,000
Asset-backed securities issued
Debt Instrument [Line Items]
Net Carrying Value	8,183,825,000	$ 7,100,661,000
Asset-backed securities issued | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Net Carrying Value	136,848,000	257,778,000
Asset-backed securities issued | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	7,804,617,000	6,637,905,000
Asset-backed securities issued | Interest-only certificates
Debt Instrument [Line Items]
Certificates	242,360,000	204,978,000
Asset-backed securities issued | Legacy Sequoia
Debt Instrument [Line Items]
Net Carrying Value	$ 239,447,000	$ 282,326,000
Number of series | series	20	20
Asset-backed securities issued | Legacy Sequoia | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Net Carrying Value	$ (35,249,000)	$ (47,805,000)
Asset-backed securities issued | Legacy Sequoia | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	0.49%	0.35%
Asset-backed securities issued | Legacy Sequoia | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	1.45%	1.55%
Asset-backed securities issued | Legacy Sequoia | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 273,957,000	$ 329,039,000
Asset-backed securities issued | Legacy Sequoia | Interest-only certificates
Debt Instrument [Line Items]
Certificates	739,000	1,092,000
Asset-backed securities issued | Sequoia
Debt Instrument [Line Items]
Net Carrying Value	$ 2,243,299,000	$ 1,347,357,000
Number of series | series	13	10
Asset-backed securities issued | Sequoia | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Net Carrying Value	$ 22,808,000	$ 32,809,000
Asset-backed securities issued | Sequoia | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	2.34%	2.25%
Asset-backed securities issued | Sequoia | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	5.07%	5.04%
Asset-backed securities issued | Sequoia | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 2,199,488,000	$ 1,309,957,000
Asset-backed securities issued | Sequoia | Interest-only certificates
Debt Instrument [Line Items]
Certificates	21,003,000	4,591,000
Asset-backed securities issued | CAFL
Debt Instrument [Line Items]
Net Carrying Value	$ 3,393,576,000	$ 3,013,093,000
Number of series | series	16	14
Asset-backed securities issued | CAFL | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Net Carrying Value	$ 68,684,000	$ 133,734,000
Asset-backed securities issued | CAFL | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	2.34%	2.68%
Asset-backed securities issued | CAFL | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	5.21%	5.42%
Asset-backed securities issued | CAFL | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 3,134,946,000	$ 2,716,425,000
Asset-backed securities issued | CAFL | Interest-only certificates
Debt Instrument [Line Items]
Certificates	189,946,000	162,934,000
Asset-backed securities issued | Freddie Mac SLST
Debt Instrument [Line Items]
Net Carrying Value	$ 1,710,664,000	$ 1,993,919,000
Number of series | series	3	3
Debt instrument, face amount	$ 163,000,000	$ 205,000,000
Asset-backed securities issued | Freddie Mac SLST | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Net Carrying Value	$ 60,625,000	$ 104,439,000
Asset-backed securities issued | Freddie Mac SLST | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	3.50%	3.50%
Asset-backed securities issued | Freddie Mac SLST | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	4.75%	4.75%
Asset-backed securities issued | Freddie Mac SLST | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 1,630,252,000	$ 1,866,145,000
Asset-backed securities issued | Freddie Mac SLST | Interest-only certificates
Debt Instrument [Line Items]
Certificates	19,787,000	23,335,000
Asset-backed securities issued | Freddie Mac K-Series
Debt Instrument [Line Items]
Net Carrying Value	$ 451,402,000	$ 463,966,000
Range of weighted average interest rates, by series	3.41%	3.39%
Number of series | series	1	1
Asset-backed securities issued | Freddie Mac K-Series | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Net Carrying Value	$ 19,863,000	$ 34,601,000
Asset-backed securities issued | Freddie Mac K-Series | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	420,654,000	416,339,000
Asset-backed securities issued | Freddie Mac K-Series | Interest-only certificates
Debt Instrument [Line Items]
Certificates	10,885,000	13,026,000
Asset-backed securities issued | Point HEI
Debt Instrument [Line Items]
Net Carrying Value	$ 145,437,000	$ 0
Range of weighted average interest rates, by series	3.27%	0.00%
Number of series | series	1	0
Asset-backed securities issued | Point HEI | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Net Carrying Value	$ 117,000	$ 0
Asset-backed securities issued | Point HEI | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	145,320,000	0
Asset-backed securities issued | Point HEI | Interest-only certificates
Debt Instrument [Line Items]
Certificates	0	$ 0
Asset-backed securities issued | CoreVest
Debt Instrument [Line Items]
Debt instrument, face amount	$ 270,000,000