Accumulated Other Comprehensive Loss (Schedule Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), before Tax	$ (164,576)	$ (305,438)
Deferred tax expense (benefit)	(37,853)	(70,251)
Accumulated other comprehensive income (loss), net of tax	(126,723)	(235,187)
Income taxes	(134,677)	(103,297)	$ (219,946)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(18,292)	(23,667)
Unrealized gains (losses) on securities available for sale
Accumulated Other Comprehensive Income (Loss), before Tax	7,522	(50,007)
Deferred tax expense (benefit)	1,730	(11,502)
Accumulated other comprehensive income (loss), net of tax	5,792	(38,505)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	5,479	270
Defined benefit pension items
Accumulated Other Comprehensive Income (Loss), before Tax	(172,098)	(163,030)
Deferred tax expense (benefit)	(39,583)	(37,497)
Accumulated other comprehensive income (loss), net of tax	(132,515)	(125,533)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(8,456)	(10,765)
Reclassification adjustment for losses included in income before income taxes	10,924	13,902
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	(10,981)	(13,981)
Unrealized losses on securities available for sale transferred from (to) held to maturity
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Before Tax	(19,889)	(17,106)
Accumulated Other Comprehensive Income (Loss), before Tax	0	(92,401)
Deferred tax expense (benefit)	0	(21,252)
Accumulated other comprehensive income (loss), net of tax	0	(71,149)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(15,315)	(13,172)
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Tax	4,574	3,934
Other Comprehensive Income (Loss) Reclassification Adjustment Of Unrealized Losses From AOCI For Securities Available For Sale Transferred To Held To Maturity Net Of Tax	$ (15,315)	$ (13,172)