Use of Special Purpose Entities and Variable Interest Entities (Loan Securitization Transaction) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Excluded principal balance associated with certain REO properties	$ 41,600
Asset-backed Securities, Securitized Loans and Receivables
Variable Interest Entity [Line Items]
Aggregate fair value	2,108,950	$ 2,232,561
Outstanding amount of Senior Bonds, at carrying value	795,912	645,027
Outstanding amount of Senior Bonds, at fair value	753,008	869,482
Outstanding amount of Senior Bonds, total	$ 1,548,920	$ 1,514,509
Weighted average interest rate	1.71%	2.11%
Weighted average contractual maturity of Senior Bonds	42 years	41 years
Cash received	$ 1,852,989	$ 1,853,408
Debt issuance cost	4,100	3,200
Senior notes
Variable Interest Entity [Line Items]
Cash received	437,900
Senior notes \| Asset-backed Securities, Securitized Loans and Receivables
Variable Interest Entity [Line Items]
Principal amount of Securitized debt	1,853,013	1,862,068
Proceeds from Senior bond sold with Step up feature	$ 505,100	568,700
Debt instrument, coupon step-up period	36 months
Senior notes \| Asset-backed Securities, Securitized Loans and Receivables \| Minimum
Variable Interest Entity [Line Items]
Debt instrument, basis spread on variable rate	1.00%
Senior notes \| Asset-backed Securities, Securitized Loans and Receivables \| Maximum
Variable Interest Entity [Line Items]
Debt instrument, basis spread on variable rate	3.00%
Senior Support Certificates \| Asset-backed Securities, Securitized Loans and Receivables
Variable Interest Entity [Line Items]
Principal amount of Securitized debt	$ 225,729	$ 268,548

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