Accumulated Other Comprehensive Income (Loss) (Schedule Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss), before Tax	$ (33,264)		$ (164,576)
Deferred tax expense (benefit)	(7,652)		(37,853)
Accumulated other comprehensive income (loss), net of tax	(25,612)		(126,723)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	10,419	$ (6,712)
Unrealized Losses on Investment Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), before Tax	132,570		7,522
Deferred tax expense (benefit)	30,490		1,730
Accumulated other comprehensive income (loss), net of tax	102,080		5,792
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	15,242	0
Unrealized Losses On Securities Available For Sale Transferred To Held To Maturity
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	(4,591)
Funded Status of Defined Benefit Plan
Accumulated Other Comprehensive Income (Loss), before Tax	(165,834)		(172,098)
Deferred tax expense (benefit)	(38,142)		(39,583)
Accumulated other comprehensive income (loss), net of tax	(127,692)		$ (132,515)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(4,823)	(2,121)
Amortization of actuarial losses and prior service cost		(2,741)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	$ 6,264	$ 2,755