Investments in Securities - Summary of Investment in Securities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Investment In Securities, Fair Value, Roll Forward Abstract [Abstract]
Beginning balance	$ 4,605,354	$ 5,178,322
Purchases	5,119,205	2,253,829
Proceeds from sales	(1,517,838)	(1,760,064)
Principal repayments	(131,356)	(870,985)
Gains (losses)	(411,314)	(147,642)
(Amortization) accretion	(6,685)	(48,106)
Ending balance	$ 7,657,366	$ 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	0	(167,202)
Principal repayments	(30,189)	(339,393)
Gains (losses)	(78,538)	(61,106)
(Amortization) accretion	(1,763)	(15,356)
Ending balance	$ 1,277,355	$ 1,387,845
Percentage of portfolio	16.68%	30.14%
Agency Trading Securities
Investment In Securities, Fair Value, Roll Forward Abstract [Abstract]
Beginning balance	$ 3,018,676	$ 3,207,420
Purchases	2,464,594	1,265,942
Proceeds from sales	0	(813,178)
Principal repayments	(101,167)	(531,592)
Gains (losses)	(254,389)	(77,145)
(Amortization) accretion	(5,723)	(32,771)
Ending balance	$ 5,121,991	$ 3,018,676
Percentage of portfolio	66.89%	65.55%
U.S. Treasuries
Investment In Securities, Fair Value, Roll Forward Abstract [Abstract]
Beginning balance	$ 198,833	$ 0
Purchases	2,654,611	987,887
Proceeds from sales	(1,517,838)	(779,684)
Principal repayments	0	0
Gains (losses)	(78,387)	(9,391)
(Amortization) accretion	801	21
Ending balance	$ 1,258,020	$ 198,833
Percentage of portfolio	16.43%	4.31%