Stockholders' Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (80,595)	$ (50,074)
Net change in unrealized gain	28,972	5,413
Reclassification of net (gain) losses realized and included in earnings	1,091	605
Amortization of unrealized net loss on securities transferred to HTM	798	647
Income tax expense	11,332	2,360
Ending Balance	(61,066)	(45,769)
Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	4,268	18,001
Net change in unrealized gain	26,882	4,421
Reclassification of net (gain) losses realized and included in earnings	$ (346)	$ (165)
Amortization of unrealized net loss on securities transferred to HTM
Income tax expense	$ 9,751	$ 1,481
Ending Balance	21,053	20,776
HTM Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (16,795)	$ (19,074)
Net change in unrealized gain
Reclassification of net (gain) losses realized and included in earnings
Amortization of unrealized net loss on securities transferred to HTM	$ 798	$ 647
Income tax expense	292	238
Ending Balance	(16,289)	(18,665)
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (67,890)	$ (48,626)
Net change in unrealized gain
Reclassification of net (gain) losses realized and included in earnings	$ 1,437	$ 770
Amortization of unrealized net loss on securities transferred to HTM
Income tax expense	$ 525	$ 280
Ending Balance	(66,978)	(48,136)
Loss on Effective Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(178)	(375)
Net change in unrealized gain	$ 2,090	$ 992
Reclassification of net (gain) losses realized and included in earnings
Amortization of unrealized net loss on securities transferred to HTM
Income tax expense	$ 764	$ 361
Ending Balance	$ 1,148	$ 256