Stockholders' Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		$ (134,402)
Net change in unrealized gain (loss)		(52,757)	$ (425)	$ (57,346)
Reclassification of net (gain) loss realized and included in earnings		34,966	5,801	4,016
Valuation adjustment for pension plan amendment			17,315
Other valuation adjustments for employee benefit plans		(45,198)	(10,929)	(12,748)
Amortization of unrealized net loss on securities transferred to held to maturity		3,296	3,786	3,830
Income tax expense (benefit)		13,386	(4,088)	22,311
Impact of re-measurement of deferred tax assets
Ending Balance		(180,709)	(134,402)
Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(29,512)	(28,679)	4,268
Net change in unrealized gain (loss)		(52,060)	6,903	(49,839)
Reclassification of net (gain) loss realized and included in earnings		25,480		(1,912)
Other valuation adjustments for employee benefit plans
Other valuation adjustments for employee benefit plans
Amortization of unrealized net loss on securities transferred to held to maturity
Income tax expense (benefit)		(5,967)	1,067	(18,804)
Impact of re-measurement of deferred tax assets	[1]		6,669
Ending Balance		(50,125)	(29,512)	(28,679)
HTM Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(14,585)	(14,392)	(16,795)
Net change in unrealized gain (loss)
Reclassification of net (gain) loss realized and included in earnings
Other valuation adjustments for employee benefit plans
Other valuation adjustments for employee benefit plans
Amortization of unrealized net loss on securities transferred to held to maturity		3,296	3,786	3,830
Income tax expense (benefit)		755	1,393	1,427
Impact of re-measurement of deferred tax assets	[1]		2,586
Ending Balance		(12,044)	(14,585)	(14,392)
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(79,078)	(72,501)	(67,890)
Net change in unrealized gain (loss)
Reclassification of net (gain) loss realized and included in earnings		4,989	5,201	5,928
Other valuation adjustments for employee benefit plans			17,315	(12,748)
Other valuation adjustments for employee benefit plans		(45,198)	(10,929)
Amortization of unrealized net loss on securities transferred to held to maturity
Income tax expense (benefit)		(9,040)	4,228	(2,209)
Impact of re-measurement of deferred tax assets	[1]		13,936
Ending Balance		(110,247)	(79,078)	(72,501)
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(11,227)	(4,960)	(178)
Net change in unrealized gain (loss)		(697)	(7,328)	(7,507)
Reclassification of net (gain) loss realized and included in earnings		4,497	600
Other valuation adjustments for employee benefit plans
Other valuation adjustments for employee benefit plans
Amortization of unrealized net loss on securities transferred to held to maturity
Income tax expense (benefit)		866	(2,600)	(2,725)
Impact of re-measurement of deferred tax assets	[1]		2,139
Ending Balance		(8,293)	(11,227)	(4,960)
Accumulated Other Comprehensive Loss, Net [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(134,402)	(120,532)	(80,595)
Net change in unrealized gain (loss)		(52,757)	(425)	(57,346)
Reclassification of net (gain) loss realized and included in earnings		34,966	5,801	4,016
Other valuation adjustments for employee benefit plans			17,315	(12,748)
Other valuation adjustments for employee benefit plans		(45,198)	(10,929)
Amortization of unrealized net loss on securities transferred to held to maturity		3,296	3,786	3,830
Income tax expense (benefit)		(13,386)	4,088	(22,311)
Impact of re-measurement of deferred tax assets	[1]		25,330
Ending Balance		(180,709)	(134,402)	$ (120,532)
Amount Reclassified from Accumulated Other Comprehensive Income [Member] | Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Valuation adjustment for pension plan amendment	[2]	$ (4,989)	$ (5,201)

[1] Represents the reclassification of stranded income tax effects to Retained Earnings upon adoption of ASU 2018-02. The adjustment is discussed in more detail later in this footnote.

[2] Amounts in parenthesis indicate reduction in net income.