Investments in Securities - Summary of Investment in Securities (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Investment In Securities, Fair Value, Roll Forward Abstract [Abstract]
Beginning balance	$ 4,605,354	$ 5,178,322
Purchases	9,281,740	2,253,829
Proceeds from sales	(5,129,788)	(1,760,064)
Receivable for unsettled sales	(427,203)
Principal repayments	(287,457)	(870,985)
Losses	(736,470)	(147,642)
(Amortization) accretion	(12,288)	(48,106)
Ending balance	$ 7,293,888	$ 4,605,354
Percentage of portfolio	100.00%	100.00%
Agency Available for Sale Securities
Investment In Securities, Fair Value, Roll Forward Abstract [Abstract]
Beginning balance	$ 1,387,845	$ 1,970,902
Purchases	0	0
Proceeds from sales	(943,314)	(167,202)
Receivable for unsettled sales	0
Principal repayments	(56,569)	(339,393)
Losses	(120,689)	(61,106)
(Amortization) accretion	(3,127)	(15,356)
Ending balance	$ 264,146	$ 1,387,845
Percentage of portfolio	3.62%	30.14%
Agency Trading Securities
Investment In Securities, Fair Value, Roll Forward Abstract [Abstract]
Beginning balance	$ 3,018,676	$ 3,207,420
Purchases	5,840,473	1,265,942
Proceeds from sales	(1,254,089)	(813,178)
Receivable for unsettled sales	(427,203)
Principal repayments	(230,888)	(531,592)
Losses	(503,411)	(77,145)
(Amortization) accretion	(10,337)	(32,771)
Ending balance	$ 6,433,221	$ 3,018,676
Percentage of portfolio	88.20%	65.55%
U.S. Treasury Securities
Investment In Securities, Fair Value, Roll Forward Abstract [Abstract]
Beginning balance	$ 198,833	$ 0
Purchases	3,441,267	987,887
Proceeds from sales	(2,932,385)	(779,684)
Receivable for unsettled sales	0
Principal repayments	0	0
Losses	(112,370)	(9,391)
(Amortization) accretion	1,176	21
Ending balance	$ 596,521	$ 198,833
Percentage of portfolio	8.18%	4.31%