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Mortgage-Backed Securities - Investment Type (Details) - USD ($)
$ in Thousands
Sep. 30, 2025
Dec. 31, 2024
Debt Securities, Trading and Available-for-sale [Abstract]    
Amortized cost $ 12,422,971 $ 6,903,832
Gross unrealized gain, investment, fair value option 171,827 11,081
Gross unrealized loss, investment, fair value option (113,961) (239,352)
Fair value through net income 12,480,837 6,675,561
Amortized cost 883,377 1,009,016
Gross unrealized gain 1,973 3,283
Gross unrealized loss (136,042) (175,773)
Fair value through OCI 749,308 836,526
Total 13,230,145 7,512,087
Residential Mortgage Backed Securities [Member] | Agency MBS    
Debt Securities, Trading and Available-for-sale [Abstract]    
Amortized cost 11,509,422 6,868,095
Gross unrealized gain, investment, fair value option 163,979 11,081
Gross unrealized loss, investment, fair value option (111,698) (237,004)
Fair value through net income 11,561,703 6,642,172
Amortized cost 773,425 827,314
Gross unrealized gain 0 0
Gross unrealized loss (131,934) (167,248)
Fair value through OCI 641,491 660,066
Total 12,203,194 7,302,238
Commercial Mortgage Backed Securities [Member] | Agency MBS    
Debt Securities, Trading and Available-for-sale [Abstract]    
Amortized cost 881,623 0
Gross unrealized gain, investment, fair value option 7,839 0
Gross unrealized loss, investment, fair value option (1,053) 0
Fair value through net income 888,409 0
Amortized cost 47,650 99,848
Gross unrealized gain 25 3
Gross unrealized loss (2,245) (4,388)
Fair value through OCI 45,430 95,463
Total 933,839 95,463
Interest-Only-Strip [Member]    
Debt Securities, Trading and Available-for-sale [Abstract]    
Amortized cost 31,926 35,737
Gross unrealized gain, investment, fair value option 9 0
Gross unrealized loss, investment, fair value option (1,210) (2,348)
Fair value through net income 30,725 33,389
Amortized cost 62,302 81,854
Gross unrealized gain 1,948 3,280
Gross unrealized loss (1,863) (4,137)
Fair value through OCI 62,387 80,997
Total 93,112 114,386
Interest-Only-Strip [Member] | Agency MBS    
Debt Securities, Trading and Available-for-sale [Abstract]    
Notional amount of nonderivative instruments 5,001,601 6,196,778
Interest-Only-Strip [Member] | Non-Agency MBS    
Debt Securities, Trading and Available-for-sale [Abstract]    
Notional amount of nonderivative instruments $ 1,140,707 $ 2,450,398