Investments in Securities - Carrying Value of Trading Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Debt and Equity Securities, FV-NI [Line Items]
Principal Amount	$ 7,332,277	$ 3,110,168
Amortized Cost	7,402,037	3,271,186
Gross Unrealized Loss	(376,629)	(54,779)
Gross Unrealized Gain	4,334	1,102
Fair Value	7,029,742	3,217,509
Agency Securities
Debt and Equity Securities, FV-NI [Line Items]
Principal Amount	6,727,277	2,910,168
Amortized Cost	6,805,676	3,072,199
Gross Unrealized Loss	(376,237)	(54,625)
Gross Unrealized Gain	3,782	1,102
Fair Value	6,433,221	3,018,676
U.S. Treasury Securities
Debt and Equity Securities, FV-NI [Line Items]
Principal Amount	605,000	200,000
Amortized Cost	596,361	198,987
Gross Unrealized Loss	(392)	(154)
Gross Unrealized Gain	552	0
Fair Value	596,521	198,833
Fannie Mae | Agency Securities
Debt and Equity Securities, FV-NI [Line Items]
Principal Amount	5,237,987	2,253,393
Amortized Cost	5,317,876	2,382,146
Gross Unrealized Loss	(326,195)	(47,079)
Gross Unrealized Gain	3,140	1,056
Fair Value	4,994,821	2,336,123
Freddie Mac | Agency Securities
Debt and Equity Securities, FV-NI [Line Items]
Principal Amount	1,489,290	656,775
Amortized Cost	1,487,800	690,053
Gross Unrealized Loss	(50,042)	(7,546)
Gross Unrealized Gain	642	46
Fair Value	$ 1,438,400	$ 682,553