Use of Special Purpose Entities and Variable Interest Entities - Loan Securitization Transaction (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Dec. 31, 2022
Variable Interest Entity [Line Items]
Weighted average fixed rate for Senior Bonds issued	4.18%	4.18%	3.70%
Senior Notes
Variable Interest Entity [Line Items]
Cash received	$ 534,800	$ 1,400,000
Asset-backed Securities, Securitized Loans and Receivables
Variable Interest Entity [Line Items]
Aggregate unpaid principal balance of residential whole loans sold	7,721,012	7,721,012	$ 6,079,749
Outstanding amount of Senior Bonds, at carrying value	801,360	801,360	922,220
Outstanding amount of Senior Bonds, at fair value	3,531,576	3,531,576	2,435,370
Outstanding amount of Senior Bonds, total	$ 4,332,936	$ 4,332,936	$ 3,357,590
Weighted average fixed rate for Senior Bonds issued	4.22%	4.22%	3.38%
Weighted average contractual maturity of Senior Bonds		37 years	38 years
Cash received		$ 6,637,607	$ 5,286,305
Debt issuance cost	$ 1,700	1,700	2,900
Asset-backed Securities, Securitized Loans and Receivables | Senior Notes
Variable Interest Entity [Line Items]
Debt instrument, face amount	6,699,921	6,699,921	5,333,090
Proceeds from Senior bond sold with Step up feature		$ 3,000,000	1,900,000
Asset-backed Securities, Securitized Loans and Receivables | Senior Notes | Minimum
Variable Interest Entity [Line Items]
Debt instrument, basis spread on variable rate (in percent)		1.00%
Debt instrument, coupon step-up period		24 months
Asset-backed Securities, Securitized Loans and Receivables | Senior Notes | Median
Variable Interest Entity [Line Items]
Debt instrument, basis spread on variable rate (in percent)		2.00%
Asset-backed Securities, Securitized Loans and Receivables | Senior Notes | Maximum
Variable Interest Entity [Line Items]
Debt instrument, basis spread on variable rate (in percent)		3.00%
Debt instrument, coupon step-up period		48 months
Asset-backed Securities, Securitized Loans and Receivables | Senior Support Certificates
Variable Interest Entity [Line Items]
Debt instrument, face amount	$ 986,585	$ 986,585	$ 715,640