Stockholders' Equity (AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 3,416,101	$ 3,261,636	$ 3,033,902
OCI before reclassifications	(3,007)	(136,097)	75,281
Amounts reclassified from AOCI	(47,234)	(52,839)	(39,739)
Other Comprehensive Income/(Loss)	(50,241)	(188,936)	35,542
Ending balance	3,383,952	3,416,101	3,261,636
Net Unrealized Gain/(Loss) on AFS Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	417,167	620,648	620,403
OCI before reclassifications	20,335	(150,642)	39,984
Amounts reclassified from AOCI	(44,780)	(52,839)	(39,739)
Other Comprehensive Income/(Loss)	(24,445)	(203,481)	245
Ending balance	392,722	417,167	620,648
Net Gain/(Loss) on Swaps
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	3,121	(11,424)	(46,721)
OCI before reclassifications	(23,342)	14,545	35,297
Amounts reclassified from AOCI	(2,454)	0	0
Other Comprehensive Income/(Loss)	(25,796)	14,545	35,297
Ending balance	(22,675)	3,121	(11,424)
Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	420,288	609,224	573,682
Ending balance	$ 370,047	$ 420,288	$ 609,224