Accumulated Other Comprehensive Income (Loss) (Schedule Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss), before Tax	$ (17,864)		$ (17,864)		$ (164,576)
Deferred tax expense (benefit)	(4,108)		(4,108)		(37,853)
Accumulated other comprehensive income (loss), net of tax	(13,756)		(13,756)		(126,723)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	11,622	$ (5,933)	27,704	$ (14,926)
Unrealized Losses on Investment Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), before Tax	135,240		135,240		7,522
Deferred tax expense (benefit)	31,105		31,105		1,730
Accumulated other comprehensive income (loss), net of tax	104,135		104,135		5,792
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	16,497	874	42,328	5,278
Unrealized Losses On Securities Available For Sale Transferred To Held To Maturity
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	(4,693)	0	(13,863)
Funded Status of Defined Benefit Plan
Accumulated Other Comprehensive Income (Loss), before Tax	(153,104)		(153,104)		(172,098)
Deferred tax expense (benefit)	(35,213)		(35,213)		(39,583)
Accumulated other comprehensive income (loss), net of tax	(117,891)		(117,891)		$ (132,515)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(4,875)	(2,114)	(14,624)	(6,341)
Amortization of actuarial losses and prior service cost		(2,730)		(8,192)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	$ 6,332	$ 2,745	$ 18,994	$ 8,235