Stockholders' Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (80,595)	$ (50,074)	$ (35,379)
Net change in unrealized gain (loss)	(57,346)	(21,270)	14,821
Reclassification of net (gain) loss realized and included in earnings	4,016	3,010	390
Valuation adjustment for employee benefit plans	(12,748)	(33,971)	(41,244)
Amortization of unrealized net loss on securities transferred to held to maturity	3,830	3,530	3,297
Income tax (benefit) expense	(22,311)	(18,180)	(8,041)
Ending Balance	(120,532)	(80,595)	(50,074)
Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	4,268	18,001	8,263
Net change in unrealized gain (loss)	(49,839)	(21,581)	15,413
Reclassification of net (gain) loss realized and included in earnings	(1,912)	(165)
Valuation adjustment for employee benefit plans
Amortization of unrealized net loss on securities transferred to held to maturity
Income tax (benefit) expense	(18,804)	(8,013)	5,675
Ending Balance	(28,679)	4,268	18,001
HTM Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(16,795)	(19,074)	(21,189)
Net change in unrealized gain (loss)
Reclassification of net (gain) loss realized and included in earnings
Valuation adjustment for employee benefit plans
Amortization of unrealized net loss on securities transferred to held to maturity	3,830	3,530	3,297
Income tax (benefit) expense	1,427	1,251	1,182
Ending Balance	(14,392)	(16,795)	(19,074)
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(67,890)	(48,626)	(22,453)
Net change in unrealized gain (loss)
Reclassification of net (gain) loss realized and included in earnings	5,928	3,175	390
Valuation adjustment for employee benefit plans	(12,748)	(33,971)	(41,244)
Amortization of unrealized net loss on securities transferred to held to maturity
Income tax (benefit) expense	(2,209)	(11,532)	(14,681)
Ending Balance	(72,501)	(67,890)	(48,626)
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(178)	(375)
Net change in unrealized gain (loss)	(7,507)	311	(592)
Reclassification of net (gain) loss realized and included in earnings
Valuation adjustment for employee benefit plans
Amortization of unrealized net loss on securities transferred to held to maturity
Income tax (benefit) expense	(2,725)	114	(217)
Ending Balance	$ (4,960)	$ (178)	$ (375)