Stockholders' Equity (Accumulated Other Comprehensive Income/(Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Components of accumulated other comprehensive income/(loss)
Balance	$ 2,526,537	$ 2,521,051	$ 2,524,802	$ 3,383,952
OCI before reclassifications	(7,820)	(7,570)	(20,538)	335,806
Amounts reclassified from AOCI	0	7,116	0	(660,594)
Other Comprehensive (Loss)	(7,820)	(454)	(20,538)	(324,788)
Balance	2,601,087	2,565,656	2,601,087	2,565,656
Total  AOCI
Components of accumulated other comprehensive income/(loss)
Balance	64,575	45,713	77,293	370,047
Balance	56,755	45,259	56,755	45,259
Net Unrealized Gain/(Loss) on AFS Securities
Components of accumulated other comprehensive income/(loss)
Balance	66,163	52,889	79,607	392,722
OCI before reclassifications	(8,029)	15,082	(21,473)	408,585
Amounts reclassified from AOCI	0	(60)	0	(733,396)
Other Comprehensive (Loss)	(8,029)	15,022	(21,473)	(324,811)
Balance	58,134	67,911	58,134	67,911
Net (Loss)/Gain on Swaps
Components of accumulated other comprehensive income/(loss)
Balance	0	(7,176)	0	(22,675)
OCI before reclassifications	0	0	0	(50,127)
Amounts reclassified from AOCI	0	7,176	0	72,802
Other Comprehensive (Loss)	0	7,176	0	22,675
Balance	0	0	0	0
Net Unrealized Gain/(Loss) on Financing Agreements
Components of accumulated other comprehensive income/(loss)
Balance	(1,588)	0	(2,314)	0
OCI before reclassifications	209	(22,652)	935	(22,652)
Amounts reclassified from AOCI	0	0	0	0
Other Comprehensive (Loss)	209	(22,652)	935	(22,652)
Balance	$ (1,379)	$ (22,652)	$ (1,379)	$ (22,652)