Stockholders' Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ 80,069	$ (54,724)
Net change in unrealized gain or loss	$ 50,135	$ 51,532	(95,355)	216,829
Reclassification of net income or loss realized and included in earnings	(3,198)	(2,885)	(2,912)	(2,517)
Valuation adjustment to employee benefit plans				(10,251)
Valuation Adjustments to Pension Plan attributable to VERIP and Curtailment			59,606
Other valuation adjustments to employee benefit plans			(10,651)
Amortization of unrealized net gain or loss on securities transferred to HTM	(45)	(94)	(101)	(289)
Income tax expense (benefit)	21,542	8,842	(12,206)	46,322
Ending Balance	42,862	102,726	42,862	102,726
Equity Method Investment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(5,369)	(434)
Net change in unrealized gain or loss			438	(984)
Reclassification of net income or loss realized and included in earnings			4,468
Ending Balance	(463)	(1,418)	(463)	(1,418)
Accumulated Other Comprehensive Loss Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			171,224	28,950
Net change in unrealized gain or loss			(96,045)	171,333
Reclassification of net income or loss realized and included in earnings			2,166
Income tax expense (benefit)			(21,095)	38,759
Ending Balance	98,440	161,524	98,440	161,524
Held to Maturity Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			276	639
Amortization of unrealized net gain or loss on securities transferred to HTM			(101)	(289)
Income tax expense (benefit)			(23)	(65)
Ending Balance	198	415	198	415
Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(125,573)	(101,278)
Reclassification of net income or loss realized and included in earnings			3,445	2,944
Valuation adjustment to employee benefit plans				(10,251)
Valuation Adjustments to Pension Plan attributable to VERIP and Curtailment			59,606
Other valuation adjustments to employee benefit plans			(10,651)
Income tax expense (benefit)			11,774	(1,653)
Ending Balance	(84,947)	(106,932)	(84,947)	(106,932)
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			39,511	17,399
Net change in unrealized gain or loss			252	46,480
Reclassification of net income or loss realized and included in earnings			(12,991)	(5,461)
Income tax expense (benefit)			(2,862)	9,281
Ending Balance	$ 29,634	$ 49,137	$ 29,634	$ 49,137