v3.26.1
Mortgage-Backed Securities - Summary of Investments in Mortgage Backed Securities (Detail) - USD ($)
$ in Thousands
Mar. 31, 2026
Dec. 31, 2025
Mortgage Backed Securities [Line Items]    
Fair value $ 3,765,539 $ 4,452,859
Mortgage Backed Securities [Member]    
Mortgage Backed Securities [Line Items]    
Principal balance or notional amount 3,764,903 4,421,692
Purchase premiums (discounts), net (111,983) (121,798)
Cumulative valuation changes 41,190 80,463
Fair value 3,694,110 4,380,357
Interest-Only Stripped Securities [Member]    
Mortgage Backed Securities [Line Items]    
Principal balance or notional amount 333,848 344,592
Fair value 71,429 72,502
Mortgage-Backed Securities Including Interest-Only Stripped Mortgage-Backed Securities [Member]    
Mortgage Backed Securities [Line Items]    
Fair value 3,765,539 4,452,859
Agency Fixed Rate Pass Through [Member] | Mortgage Backed Securities [Member]    
Mortgage Backed Securities [Line Items]    
Principal balance or notional amount 2,246,463 2,805,895
Purchase premiums (discounts), net 771 (2,125)
Cumulative valuation changes 18,919 46,677
Fair value 2,266,153 2,850,447
Floating Rate Collateralized Mortgage Obligations [Member] | Mortgage Backed Securities [Member]    
Mortgage Backed Securities [Line Items]    
Principal balance or notional amount 822,780 850,172
Purchase premiums (discounts), net (994) (1,249)
Cumulative valuation changes 7,806 7,074
Fair value 829,592 855,997
Principal-only Stripped [Member] | Mortgage Backed Securities [Member]    
Mortgage Backed Securities [Line Items]    
Principal balance or notional amount 549,048 610,256
Purchase premiums (discounts), net (108,778) (115,385)
Cumulative valuation changes 15,639 26,258
Fair value 455,909 521,129
Senior Non-Agency [Member] | Mortgage Backed Securities [Member]    
Mortgage Backed Securities [Line Items]    
Principal balance or notional amount 142,612 155,369
Purchase premiums (discounts), net (2,982) (3,039)
Cumulative valuation changes (1,174) 454
Fair value 138,456 $ 152,784
Subordinate Residential Transition [Member] | Mortgage Backed Securities [Member]    
Mortgage Backed Securities [Line Items]    
Principal balance or notional amount 4,000  
Purchase premiums (discounts), net 0  
Cumulative valuation changes 0  
Fair value $ 4,000