CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME/(LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net (loss)/income	$ (679,390)	$ 378,117	$ 301,801
Other Comprehensive Income/(Loss):
Unrealized gains on securities available-for-sale	420,281	20,335	(150,642)
Reclassification adjustment for MBS sales included in net income	389,127	44,600	51,580
Reclassification adjustment for impairments included in net income	(344,269)	(180)	(1,259)
Derivative hedging instrument fair value changes, net	(50,127)	(23,342)	14,545
Changes in fair value of financing agreements at fair value due to changes in instrument-specific credit risk	(2,314)	0	0
Reclassification adjustment for losses/gains related to hedging instruments included in net income	72,802	(2,454)	0
Other Comprehensive Loss	(292,754)	(50,241)	(188,936)
Comprehensive (loss)/ income before preferred stock dividends	(972,144)	327,876	112,865
Dividends required on preferred stock	(29,796)	(15,000)	(15,000)
Comprehensive (Loss)/Income Available to Common Stock and Participating Securities	$ (1,001,940)	$ 312,876	$ 97,865