Stockholders' Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ (54,724)	$ (180,709)
Net change in unrealized gain or loss	$ 425	$ 34,159	217,254	160,627
Reclassification of net income or loss realized and included in earnings	(4,076)	3,280	(6,593)	11,483
Valuation adjustment to employee benefit plans			(10,251)	(7,015)
Amortization of unrealized net loss (gain) on securities transferred to HTM	(89)	954	(378)	2,435
Income tax expense	48	7,331	46,370	37,977
Ending Balance	98,938	(51,156)	98,938	(51,156)
Equity Method Investment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(434)
Net change in unrealized gain or loss			(4,935)	(434)
Ending Balance	(5,369)	(434)	(5,369)	(434)
Accumulated Other Comprehensive Loss Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			28,950	(50,125)
Net change in unrealized gain or loss			176,009	125,589
Income tax expense			39,817	28,395
Ending Balance	165,142	47,069	165,142	47,069
Held to Maturity Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			639	(12,044)
Amortization of unrealized net loss (gain) on securities transferred to HTM			(378)	2,435
Income tax expense			(85)	551
Ending Balance	346	(10,160)	346	(10,160)
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(101,278)	(110,247)
Reclassification of net income or loss realized and included in earnings			4,656	6,851
Valuation adjustment to employee benefit plans			(10,251)	(7,015)
Income tax expense			(1,265)	(37)
Ending Balance	(105,608)	(110,374)	(105,608)	(110,374)
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			17,399	(8,293)
Net change in unrealized gain or loss			46,180	35,472
Reclassification of net income or loss realized and included in earnings			(11,249)	4,632
Income tax expense			7,903	9,068
Ending Balance	$ 44,427	$ 22,743	$ 44,427	$ 22,743