Stockholders' Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ (180,709)	$ (134,402)
Net change in unrealized gain or loss	$ 34,159	$ (25,242)	160,627	(110,895)
Reclassification of net loss realized and included in earnings	3,280	2,547	11,483	6,560
Valuation adjustment employee benefit plan			(7,015)	(9,039)
Amortization of unrealized net loss on securities transferred to HTM	954	747	2,435	2,427
Income tax expense (benefit)	7,331	(4,978)	37,977	(25,170)
Ending Balance	(51,156)	(220,179)	(51,156)	(220,179)
Equity Method Investment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net change in unrealized gain or loss			(434)
Ending Balance	(434)		(434)
Accumulated Other Comprehensive Loss Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(50,125)	(29,512)
Net change in unrealized gain or loss			125,589	(92,477)
Income tax expense (benefit)			28,395	(20,985)
Ending Balance	47,069	(101,004)	47,069	(101,004)
Held to Maturity Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(12,044)	(14,585)
Amortization of unrealized net loss on securities transferred to HTM			2,435	2,427
Income tax expense (benefit)			551	550
Ending Balance	(10,160)	(12,708)	(10,160)	(12,708)
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(110,247)	(79,078)
Reclassification of net loss realized and included in earnings			6,851	3,719
Valuation adjustment employee benefit plan			(7,015)	(9,039)
Income tax expense (benefit)			(37)	(1,205)
Ending Balance	(110,374)	(83,193)	(110,374)	(83,193)
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(8,293)	(11,227)
Net change in unrealized gain or loss			35,472	(18,418)
Reclassification of net loss realized and included in earnings			4,632	2,841
Income tax expense (benefit)			9,068	(3,530)
Ending Balance	$ 22,743	$ (23,274)	$ 22,743	$ (23,274)