v3.26.1
Investments in Securities - Schedule of Available-for-sale Securities in an Unrealized Gain or Loss Position (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Debt and Equity Securities, FV-NI [Line Items]    
Principal Amount $ 21,487,102 $ 19,980,804
Amortized Cost 21,267,012 19,855,846
Gross Unrealized Loss (203,479) (88,906)
Gross Unrealized Gain 120,111 248,809
Fair Value 21,183,644 20,015,749
Agency Securities    
Debt and Equity Securities, FV-NI [Line Items]    
Principal Amount 20,887,102 19,380,804
Amortized Cost 20,667,692 19,257,086
Gross Unrealized Loss (191,507) (87,828)
Gross Unrealized Gain 120,111 248,382
Fair Value 20,596,296 19,417,640
U.S. Treasury Securities    
Debt and Equity Securities, FV-NI [Line Items]    
Principal Amount 600,000 600,000
Amortized Cost 599,320 598,760
Gross Unrealized Loss (11,972) (1,078)
Gross Unrealized Gain 0 427
Fair Value $ 587,348 $ 598,109