Mortgage-Backed Securities - Components of Carrying Value of MBS and GSE CRT Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Principal/notional balance	$ 6,536,025		$ 5,864,813
Unamortized premium	17,355		5,061
Unamortized discount	(845,063)		(931,456)
Allowance for Credit Losses	(542)	$ 622	(320)	$ (212)	$ 169	$ 0
Gross unrealized gains	170,389		111,422
Gross unrealized losses	(4,468)		(4,214)
Total Fair Value	5,873,696		5,045,306
MBS
Debt Securities, Available-for-sale [Line Items]
Principal/notional balance	5,750,928		5,025,062
Unamortized premium	17,355		5,061
Unamortized discount	(131,667)		(169,342)
Allowance for Credit Losses	(542)		(320)
Gross unrealized gains	163,888		107,899
Gross unrealized losses	(1,835)		(393)
Total Fair Value	5,798,127		4,967,967
Interest-Only Securities
Debt Securities, Available-for-sale [Line Items]
Principal/notional balance	785,097		839,751
Unamortized premium	0		0
Unamortized discount	(713,396)		(762,114)
Allowance for Credit Losses	0		0
Gross unrealized gains	6,501		3,523
Gross unrealized losses	(2,633)		(3,821)
Total Fair Value	$ 75,569		$ 77,339