Accumulated Other Comprehensive Income (Loss) (Schedule Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss), before Tax	$ (12,552)		$ (12,552)		$ (164,576)
Deferred tax expense (benefit)	(2,888)		(2,888)		(37,853)
Accumulated other comprehensive income (loss), net of tax	(9,664)		(9,664)		(126,723)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	5,663	$ (2,281)	16,082	$ (8,993)
Unrealized Losses on Investment Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), before Tax	146,884		146,884		7,522
Deferred tax expense (benefit)	33,782		33,782		1,730
Accumulated other comprehensive income (loss), net of tax	113,102		113,102		5,792
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	10,589	4,404	25,831	4,404
Unrealized Losses On Securities Available For Sale Transferred To Held To Maturity
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	(4,579)	0	(9,170)
Funded Status of Defined Benefit Plan
Accumulated Other Comprehensive Income (Loss), before Tax	(159,436)		(159,436)		(172,098)
Deferred tax expense (benefit)	(36,670)		(36,670)		(39,583)
Accumulated other comprehensive income (loss), net of tax	(122,766)		(122,766)		$ (132,515)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(4,926)	(2,106)	(9,749)	(4,227)
Amortization of actuarial losses and prior service cost		(2,721)		(5,462)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	$ 6,398	$ 2,735	$ 12,662	$ 5,490