Investments in Securities - Unrealized Gain or Loss Position and Components of Carrying Value of Available for Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Weighted average coupon rate	4.34%	3.83%
Principal Amount	$ 260,363	$ 1,248,910
Amortized Cost	270,361	1,280,872
Gross Unrealized Loss	(6,215)	(45)
Gross Unrealized Gain	0	107,018
Fair Value	264,146	1,387,845
Fannie Mae
Debt Securities, Available-for-sale [Line Items]
Principal Amount	116,932	1,063,403
Amortized Cost	121,254	1,088,209
Gross Unrealized Loss	(2,512)	(21)
Gross Unrealized Gain	0	99,138
Fair Value	118,742	1,187,326
Freddie Mac
Debt Securities, Available-for-sale [Line Items]
Principal Amount	143,345	172,550
Amortized Cost	149,017	179,385
Gross Unrealized Loss	(3,702)	(4)
Gross Unrealized Gain	0	7,797
Fair Value	145,315	187,178
Ginnie Mae
Debt Securities, Available-for-sale [Line Items]
Principal Amount	86	12,957
Amortized Cost	90	13,278
Gross Unrealized Loss	(1)	(20)
Gross Unrealized Gain	0	83
Fair Value	$ 89	$ 13,341