Mortgage-Backed and Credit Risk Transfer Securities - Realized Gain (Loss) on Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Gross realized gains on sale of investments	$ 3,297	$ 656,915	$ 24,721
Gross realized losses on sale of investments	(284,521)	(1,020,696)	(16,682)
Impairment of investments the Company intends to sell or more likely than not will be required to sell before recovery of amortized cost basis and other impairments	0	(101,138)	0
Other-than-temporary impairment losses	0	0	(7,731)
Net unrealized gains (losses) on MBS and GSE CRT accounted for under the fair value option	(85,702)	(492,047)	624,158
Net unrealized gains (losses) on commercial loan	417	(1,164)	0
Realized loss on loan participation interest	0	(3,808)	0
Total gain (loss) on investments, net	$ (366,509)	$ (961,938)	$ 624,466