Stockholders' Equity (AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
OCI before reclassifications	$ (136,097)	$ 75,281	$ 95,238
Amounts reclassified from AOCI	(52,839)	(39,739)	(37,407)
Other Comprehensive Income/(Loss)	(188,936)	35,542	57,831
Net Unrealized Gain/(Loss) on AFS Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	620,648	620,403	585,250
OCI before reclassifications	(150,642)	39,984	72,560
Amounts reclassified from AOCI	(52,839)	(39,739)	(37,407)
Other Comprehensive Income/(Loss)	(203,481)	245	35,153
Balance at end of period	417,167	620,648	620,403
Net Gain/(Loss) on Swaps
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(11,424)	(46,721)	(69,399)
OCI before reclassifications	14,545	35,297	22,678
Amounts reclassified from AOCI	0	0	0
Other Comprehensive Income/(Loss)	14,545	35,297	22,678
Balance at end of period	3,121	(11,424)	(46,721)
Accumulated Other Comprehensive Income
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	609,224	573,682	515,851
Balance at end of period	$ 420,288	$ 609,224	$ 573,682