v3.26.3
Investments in Securities - Schedule of Available-for-sale Securities in an Unrealized Gain or Loss Position (Details) - USD ($)
$ in Thousands
Sep. 30, 2026
Dec. 31, 2025
Debt and Equity Securities, FV-NI [Line Items]    
Principal Amount $ 21,911,666 $ 19,980,804
Amortized Cost 21,688,779 19,855,846
Gross Unrealized Loss (1,222,887) (88,906)
Gross Unrealized Gain 0 248,809
Fair Value 20,465,892 20,015,749
Agency Securities    
Debt and Equity Securities, FV-NI [Line Items]    
Principal Amount 21,411,666 19,380,804
Amortized Cost 21,189,942 19,257,086
Gross Unrealized Loss (1,198,025) (87,828)
Gross Unrealized Gain 0 248,382
Fair Value 19,991,917 19,417,640
U.S. Treasury Securities    
Debt and Equity Securities, FV-NI [Line Items]    
Principal Amount 500,000 600,000
Amortized Cost 498,837 598,760
Gross Unrealized Loss (24,862) (1,078)
Gross Unrealized Gain 0 427
Fair Value $ 473,975 $ 598,109