Asset-Backed Securities Issued - Components of Asset-Backed Securities Issued by Consolidated Securitization Entities Sponsored, Along With Other Selected Information (Details) - Asset-backed securities issued	Sep. 30, 2020 USD ($) series	Dec. 31, 2019 USD ($) series
Debt Instrument [Line Items]
Long-term debt	$ 7,172,398,000	$ 10,515,475,000
Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	198,057,000	197,110,000
Certificates with principal balance
Debt Instrument [Line Items]
Certificates	6,792,029,000	9,962,253,000
Interest-only certificates
Debt Instrument [Line Items]
Certificates	182,312,000	356,112,000
Legacy Sequoia
Debt Instrument [Line Items]
Long-term debt	$ 292,484,000	$ 402,465,000
Number of series | series	20	20
Legacy Sequoia | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	$ (56,769,000)	$ (18,873,000)
Legacy Sequoia | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	0.35%	1.94%
Legacy Sequoia | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	1.96%	3.26%
Legacy Sequoia | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 347,985,000	$ 420,056,000
Legacy Sequoia | Interest-only certificates
Debt Instrument [Line Items]
Certificates	1,268,000	1,282,000
Sequoia Choice
Debt Instrument [Line Items]
Long-term debt	$ 1,626,564,000	$ 2,037,198,000
Number of series | series	10	9
Sequoia Choice | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	$ 48,045,000	$ 40,965,000
Sequoia Choice | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	2.23%	4.40%
Sequoia Choice | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	5.02%	5.05%
Sequoia Choice | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 1,571,714,000	$ 1,979,719,000
Sequoia Choice | Interest-only certificates
Debt Instrument [Line Items]
Certificates	6,805,000	16,514,000
Freddie Mac SLST
Debt Instrument [Line Items]
Long-term debt	$ 2,044,335,000	$ 1,918,322,000
Range of weighted average interest rates, by series		3.50%
Number of series | series	3	2
Debt instrument, face amount	$ 208,000,000
Freddie Mac SLST | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	$ 95,138,000	$ 45,349,000
Freddie Mac SLST | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	3.50%
Freddie Mac SLST | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	4.75%
Freddie Mac SLST | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 1,925,144,000	1,842,682,000
Freddie Mac SLST | Interest-only certificates
Debt Instrument [Line Items]
Certificates	24,053,000	30,291,000
Freddie Mac K-Series
Debt Instrument [Line Items]
Long-term debt	$ 464,865,000	$ 4,156,239,000
Range of weighted average interest rates, by series	3.39%
Number of series | series	1	5
Freddie Mac K-Series | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	$ 33,531,000	$ 93,559,000
Freddie Mac K-Series | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series		3.35%
Freddie Mac K-Series | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series		4.35%
Freddie Mac K-Series | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	418,212,000	$ 3,844,789,000
Freddie Mac K-Series | Interest-only certificates
Debt Instrument [Line Items]
Certificates	13,122,000	217,891,000
CAFL
Debt Instrument [Line Items]
Long-term debt	$ 2,744,150,000	$ 2,001,251,000
Number of series | series	13	10
CAFL | Revision of Prior Period, Accounting Standards Update, Adjustment
Debt Instrument [Line Items]
Long-term debt	$ 78,112,000	$ 36,110,000
CAFL | Minimum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	3.18%	3.25%
CAFL | Maximum
Debt Instrument [Line Items]
Range of weighted average interest rates, by series	5.53%	5.36%
CAFL | Certificates with principal balance
Debt Instrument [Line Items]
Certificates	$ 2,528,974,000	$ 1,875,007,000
CAFL | Interest-only certificates
Debt Instrument [Line Items]
Certificates	$ 137,064,000	$ 90,134,000