Stockholders' Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (120,532)	$ (80,595)
Net change in unrealized gain (loss)	1,184	28,972
Reclassification of net (gain) loss realized and included in earnings	1,387	1,091
Amortization of unrealized net loss (gain) on securities transferred to HTM	650	798
Income tax expense (benefit)	1,201	11,332
Ending Balance	(118,512)	(61,066)
Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(28,679)	4,268
Net change in unrealized gain (loss)	2,319	26,882
Reclassification of net (gain) loss realized and included in earnings		(346)
Amortization of unrealized net loss (gain) on securities transferred to HTM
Income tax expense (benefit)	843	9,751
Ending Balance	(27,203)	21,053
HTM Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(14,392)	(16,795)
Net change in unrealized gain (loss)
Reclassification of net (gain) loss realized and included in earnings
Amortization of unrealized net loss (gain) on securities transferred to HTM	650	798
Income tax expense (benefit)	266	292
Ending Balance	(14,008)	(16,289)
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(72,501)	(67,890)
Net change in unrealized gain (loss)
Reclassification of net (gain) loss realized and included in earnings	1,387	1,437
Amortization of unrealized net loss (gain) on securities transferred to HTM
Income tax expense (benefit)	504	525
Ending Balance	(71,618)	(66,978)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(4,960)	(178)
Net change in unrealized gain (loss)	(1,135)	2,090
Reclassification of net (gain) loss realized and included in earnings
Amortization of unrealized net loss (gain) on securities transferred to HTM
Income tax expense (benefit)	(412)	764
Ending Balance	$ (5,683)	$ 1,148