Securitized Debt - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Gains (losses) on extinguishment of debt	$ (25,622,000)	$ (55,794,000)	$ (284,535,000)	$ (55,338,000)
Non-Agency RMBS
Debt Instrument [Line Items]
Gains (losses) on extinguishment of debt		(56,000,000)
Securitized Loans | Non-Agency RMBS | Variable Interest Entities, Primary Beneficiary
Debt Instrument [Line Items]
Principal balance	$ 116,000,000		$ 116,000,000		$ 135,000,000
Weighted average cost of financing	6.70%		6.70%		6.50%
Acquired securitized debt collateral outstanding principal balance	$ 189,000,000	0	$ 3,900,000,000	147,000,000
Repurchase of non retained secured debt	193,000,000	$ 0	4,200,000,000
Gains (losses) on extinguishment of debt	(4,000,000)		(260,000,000)	$ 459,000
Securitized Loans | Securitized debt | Variable Interest Entities, Primary Beneficiary
Debt Instrument [Line Items]
Principal balance	$ 7,900,000,000		$ 7,900,000,000		$ 8,700,000,000
Weighted average cost of financing	2.40%		2.40%		3.40%