Mortgage-Backed and Credit Risk Transfer Securities - Schedule of Fair Value of Available-for-sale Securities and Securities Accounted for under Fair Value Option by Asset Type (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Percentage of MBS and GSE CRT accounted for under the fair value option	99.00%	99.00%
Available-for-sale Securities	$ 70,197	$ 116,850
Securities under Fair Value Option	7,734,062	8,055,332
Total Fair Value	7,804,259	8,172,182
30 year fixed-rate
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0	0
Securities under Fair Value Option	7,701,523	8,050,866
Total Fair Value	7,701,523	8,050,866
Total Agency RMBS pass-through
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0	0
Securities under Fair Value Option	7,701,523	8,050,866
Total Fair Value	7,701,523	8,050,866
Agency-CMO
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	0	0
Securities under Fair Value Option	30,757	0
Total Fair Value	30,757	0
Non-Agency CMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	62,909	109,583
Securities under Fair Value Option	0	0
Total Fair Value	62,909	109,583
Non-Agency RMBS
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	7,288	7,267
Securities under Fair Value Option	1,782	4,466
Total Fair Value	$ 9,070	$ 11,733