Accumulated Other Comprehensive Income (Loss) (Schedule Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), before Tax		$ (268,650)		$ (305,438)
Deferred tax expense (benefit)		(61,790)		(70,251)
Accumulated other comprehensive income (loss), net of tax		(206,860)	$ (230,323)	(235,187)	$ (122,294)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(6,712)	(2,569)
Amortization of actuarial losses and prior service cost		(2,741)	(3,317)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax		2,755	3,337
Unrealized Losses on Investment Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), before Tax		(21,936)		(50,007)
Deferred tax expense (benefit)		(5,046)		(11,502)
Accumulated other comprehensive income (loss), net of tax	[1]	(16,890)	(121,243)	(38,505)	(30,945)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	0	0
Unrealized Losses On Securities Available For Sale Transferred To Held To Maturity
Accumulated Other Comprehensive Income (Loss), before Tax		(86,439)		(92,401)
Deferred tax expense (benefit)		(19,881)		(21,252)
Accumulated other comprehensive income (loss), net of tax	[1]	(66,558)	0	(71,149)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	(4,591)	0
Funded Status of Defined Benefit Plan
Accumulated Other Comprehensive Income (Loss), before Tax		(160,275)		(163,030)
Deferred tax expense (benefit)		(36,863)		(37,497)
Accumulated other comprehensive income (loss), net of tax	[1]	(123,412)	(109,080)	$ (125,533)	$ (91,349)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	$ (2,121)	$ (2,569)

[1] All amounts are net of tax. Amounts in parentheses indicate debits.