Stockholders' Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		$ (180,709)	$ (134,402)	$ (120,532)
Net change in unrealized gain (loss)		143,922	(52,757)	(425)
Reclassification of net (gain) loss realized and included in earnings		13,429	34,966	5,801
Valuation adjustment for employee benefit plan amendment		2,398	(45,198)	17,315
Other valuation adjustments of employee benefit plans		2,398	(45,198)	(10,929)
Amortization of unrealized net loss on securities transferred to held to maturity		3,153	3,296	3,786
Income tax expense (benefit)		36,917	(13,386)	4,088
Impact of re-measurement of deferred tax assets	[1]			25,330
Ending Balance		(54,724)	(180,709)	(134,402)
Accumulated Other Comprehensive Loss Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(50,125)	(29,512)	(28,679)
Net change in unrealized gain (loss)		115,413	(52,060)	6,903
Reclassification of net (gain) loss realized and included in earnings			25,480
Unrealized loss on securities transferred to available for sale		(13,236)
Income tax expense (benefit)		23,102	(5,967)	1,067
Impact of re-measurement of deferred tax assets	[1]			6,669
Ending Balance		28,950	(50,125)	(29,512)
Held to Maturity Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(12,044)	(14,585)	(14,392)
Unrealized loss on securities transferred to available for sale		13,236
Amortization of unrealized net loss on securities transferred to held to maturity		3,153	3,296	3,786
Income tax expense (benefit)		3,706	755	1,393
Impact of re-measurement of deferred tax assets	[1]			2,586
Ending Balance		639	(12,044)	(14,585)
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(110,247)	(79,078)	(72,501)
Reclassification of net (gain) loss realized and included in earnings		9,174	4,989	5,201
Valuation adjustment for employee benefit plan amendment		2,398	(45,198)	17,315
Other valuation adjustments of employee benefit plans				(10,929)
Income tax expense (benefit)		2,603	(9,040)	4,228
Impact of re-measurement of deferred tax assets	[1]			13,936
Ending Balance		(101,278)	(110,247)	(79,078)
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(8,293)	(11,227)	(4,960)
Net change in unrealized gain (loss)		28,943	(697)	(7,328)
Reclassification of net (gain) loss realized and included in earnings		4,255	4,497	600
Income tax expense (benefit)		7,506	866	(2,600)
Impact of re-measurement of deferred tax assets	[1]			2,139
Ending Balance		17,399	$ (8,293)	$ (11,227)
Equity Method Investment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net change in unrealized gain (loss)		(434)
Ending Balance		$ (434)

[1] Represents the reclassification of stranded income tax effects to Retained Earnings upon adoption of ASU 2018-02.