Mortgage-Backed Securities - Investment Portfolio (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023	Jun. 30, 2024	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 (Discount)	(827,708)	(926,395)
Amortized Cost	5,708,317	4,938,418
Allowance for Credit Losses	(542)	(320)	$ 622	$ (212)	$ 169	$ 0
Unrealized Gain/ (Loss), net	165,921	107,208
Fair Value	$ 5,873,696	$ 5,045,306
Period-end weighted average yield	5.41%	5.42%
Unamortized premium (discount) non-accretable portion	$ 2,100
Percentage of non-agency RMBS interest-only, principal balance	96.70%	96.90%
Percentage of non-agency RMBS interest-only, amortized cost	34.40%	37.60%
Percentage of non-agency RMBS interest only, fair value	30.90%	31.70%
30 year fixed-rate pass-through
Debt Securities, Available-for-sale [Line Items]
Principal/ Notional Balance	$ 5,066,865	$ 5,005,512
Unamortized Premium (Discount)	(105,046)	(159,924)
Amortized Cost	4,961,819	4,845,588
Allowance for Credit Losses	0	0
Unrealized Gain/ (Loss), net	145,995	106,886
Fair Value	$ 5,107,814	$ 4,952,474
Period-end weighted average yield	5.43%	5.33%
Agency-CMO
Debt Securities, Available-for-sale [Line Items]
Principal/ Notional Balance	$ 539,741	$ 573,240
Unamortized Premium (Discount)	(470,393)	(498,355)
Amortized Cost	69,348	74,885
Allowance for Credit Losses	0	0
Unrealized Gain/ (Loss), net	3,851	(127)
Fair Value	$ 73,199	$ 74,758
Period-end weighted average yield	9.91%	9.74%
Agency CMBS
Debt Securities, Available-for-sale [Line Items]
Principal/ Notional Balance	$ 664,661
Unamortized Premium (Discount)	(5,342)
Amortized Cost	659,319
Allowance for Credit Losses	0
Unrealized Gain/ (Loss), net	15,755
Fair Value	$ 675,074
Period-end weighted average yield	4.64%
Non-Agency CMBS
Debt Securities, Available-for-sale [Line Items]
Principal/ Notional Balance	$ 11,000	$ 11,000
Unamortized Premium (Discount)	0	(372)
Amortized Cost	11,000	10,628
Allowance for Credit Losses	(542)	(320)
Unrealized Gain/ (Loss), net	(522)	(373)
Fair Value	$ 9,936	$ 9,935
Period-end weighted average yield	8.91%	9.58%
Non-Agency RMBS
Debt Securities, Available-for-sale [Line Items]
Principal/ Notional Balance	$ 253,758	$ 275,061
Unamortized Premium (Discount)	(246,927)	(267,744)
Amortized Cost	6,831	7,317
Allowance for Credit Losses	0	0
Unrealized Gain/ (Loss), net	842	822
Fair Value	$ 7,673	$ 8,139
Period-end weighted average yield	9.31%	9.10%
Percentage of non-agency securities classified as fixed rate	66.10%	66.80%
Percentage of non-agency securities classified as variable rate	33.20%	32.50%
Percentage of non-agency securities classified as floating rate	0.70%	0.70%
Unamortized premium (discount) non-accretable portion		$ 2,100