Stockholders' Equity (AOCI Reclassifications) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized (loss)/gain on sales of residential mortgage securities and residential whole loans	$ 0	$ 49,485	$ 0	$ (188,895)
Other, net	9,127	1,264	9,096	738
Net Income/(Loss) Available to Common Stock and Participating Securities	58,495	88,434	135,798	(825,776)
Derivative hedging instrument fair value changes, net	0	0	0	(50,126)
Amounts reclassified from AOCI	0	(80,704)	0	(667,711)
Amounts Reclassified from AOCI | AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Including Noncontrolling Interest
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized (loss)/gain on sales of residential mortgage securities and residential whole loans	0	(144,736)	0	(389,067)
Other, net	0	0	0	(344,269)
Net Income/(Loss) Available to Common Stock and Participating Securities	$ 0	(144,736)	$ 0	(733,336)
Amounts Reclassified from AOCI | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of de-designated hedging instruments		64,032		65,625
Derivative hedging instrument fair value changes, net		$ 64,032		$ 65,625