Use of Special Purpose Entities and Variable Interest Entities - Loan Securitization Transaction (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Variable Interest Entity [Line Items]
Weighted average fixed rate for Senior Bonds issued	4.52%	4.33%
Senior Notes
Variable Interest Entity [Line Items]
Cash received	$ 160,000
Asset-backed Securities, Securitized Loans and Receivables
Variable Interest Entity [Line Items]
Aggregate unpaid principal balance of residential whole loans sold	8,433,573	$ 8,241,053
Outstanding amount of Senior Bonds, at carrying value	728,770	765,433
Outstanding amount of Senior Bonds, at fair value	4,065,630	3,985,372
Outstanding amount of Senior Bonds, total	$ 4,794,400	$ 4,750,805
Weighted average fixed rate for Senior Bonds issued	4.62%	4.51%
Weighted average contractual maturity of Senior Bonds	35 years	36 years
Cash received	$ 7,249,574	$ 7,089,575
Debt issuance cost	1,400	1,500
Asset-backed Securities, Securitized Loans and Receivables | Senior Notes
Variable Interest Entity [Line Items]
Debt instrument, face amount	7,312,213	7,152,213
Proceeds from Senior bond sold with Step up feature	$ 3,400,000	3,400,000
Asset-backed Securities, Securitized Loans and Receivables | Senior Notes | Variable Rate, Option 1
Variable Interest Entity [Line Items]
Debt instrument, basis spread on variable rate (in percent)	1.00%
Asset-backed Securities, Securitized Loans and Receivables | Senior Notes | Variable Rate, Option 2
Variable Interest Entity [Line Items]
Debt instrument, basis spread on variable rate (in percent)	1.50%
Asset-backed Securities, Securitized Loans and Receivables | Senior Notes | Variable Rate, Option 3
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 | Variable Rate, Option 4
Variable Interest Entity [Line Items]
Debt instrument, basis spread on variable rate (in percent)	3.00%
Asset-backed Securities, Securitized Loans and Receivables | Senior Notes | Minimum
Variable Interest Entity [Line Items]
Debt instrument, coupon step-up period	24 months
Asset-backed Securities, Securitized Loans and Receivables | Senior Notes | Maximum
Variable Interest Entity [Line Items]
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	$ 1,077,297	$ 1,047,297