Stockholders' Equity (Components of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ 80,069	$ (54,724)
Net change in unrealized gain or loss	$ (48,569)	$ 425	(143,924)	217,254
Reclassification of net income or loss realized and included in earnings	(6,425)	(4,076)	(9,337)	(6,593)
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	(33)	(89)	(134)	(378)
Income tax expense (benefit)	(12,363)	48	(24,569)	46,370
Ending Balance	198	98,938	198	98,938
Equity Method Investment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(5,369)	(434)
Net change in unrealized gain or loss			438	(4,935)
Reclassification of net income or loss realized and included in earnings			4,468
Ending Balance	(463)	(5,369)	(463)	(5,369)
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			(144,715)	176,009
Reclassification of net income or loss realized and included in earnings			2,166
Income tax expense (benefit)			(31,952)	39,817
Ending Balance	60,627	165,142	60,627	165,142
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			(134)	(378)
Income tax expense (benefit)			(30)	(85)
Ending Balance	172	346	172	346
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			3,970	4,656
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)			11,783	(1,265)
Ending Balance	(84,431)	(105,608)	(84,431)	(105,608)
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			353	46,180
Reclassification of net income or loss realized and included in earnings			(19,941)	(11,249)
Income tax expense (benefit)			(4,370)	7,903
Ending Balance	$ 24,293	$ 44,427	$ 24,293	$ 44,427