Investments in Securities - Carrying Value of Trading Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Debt and Equity Securities, FV-NI [Line Items]
Principal Amount	$ 8,758,304	$ 3,110,168
Amortized Cost	8,810,229	3,271,186
Gross Unrealized Loss	(758,463)	(54,779)
Gross Unrealized Gain	0	1,102
Fair Value	8,051,766	3,217,509
Agency Securities
Debt and Equity Securities, FV-NI [Line Items]
Principal Amount	8,458,304	2,910,168
Amortized Cost	8,534,889	3,072,199
Gross Unrealized Loss	(757,295)	(54,625)
Gross Unrealized Gain	0	1,102
Fair Value	7,777,594	3,018,676
U.S. Treasury Securities
Debt and Equity Securities, FV-NI [Line Items]
Principal Amount	300,000	200,000
Amortized Cost	275,340	198,987
Gross Unrealized Loss	(1,168)	(154)
Gross Unrealized Gain	0	0
Fair Value	274,172	198,833
Fannie Mae | Agency Securities
Debt and Equity Securities, FV-NI [Line Items]
Principal Amount	5,648,405	2,253,393
Amortized Cost	5,722,619	2,382,146
Gross Unrealized Loss	(565,610)	(47,079)
Gross Unrealized Gain	0	1,056
Fair Value	5,157,009	2,336,123
Freddie Mac | Agency Securities
Debt and Equity Securities, FV-NI [Line Items]
Principal Amount	2,809,899	656,775
Amortized Cost	2,812,270	690,053
Gross Unrealized Loss	(191,685)	(7,546)
Gross Unrealized Gain	0	46
Fair Value	$ 2,620,585	$ 682,553