Use of Special Purpose Entities and Variable Interest Entities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Total residential whole loans	$ 7,100,000	$ 7,100,000	$ 5,300,000
Asset-backed Securities, Securitized Loans and Receivables
Variable Interest Entity [Line Items]
Proceeds from issuance of debt		2,788,354	1,853,408
Residential whole loans	2,300,000	2,300,000	1,800,000
Securitized debt	2,000,000	2,000,000	1,500,000
Asset-backed Securities, Securitized Loans and Receivables | Other Assets
Variable Interest Entity [Line Items]
Real estate owned at fair value	36,100	36,100	$ 49,500
Senior Bonds
Variable Interest Entity [Line Items]
Proceeds from issuance of debt	277,300	1,500,000
Proceed from debt net of offering expenses and underwriting discount	$ 277,300	$ 1,500,000