Accumulated Other Comprehensive Income (Loss) (Schedule Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), before Tax		$ (162,981)		$ (162,981)			$ (214,481)
Deferred tax expense (benefit)		(60,138)		(60,138)			(79,289)
Accumulated other comprehensive income (loss), net of tax		(102,843)	$ (15,027)	(102,843)	$ (15,027)	$ (110,941)	(135,192)	$ (23,824)	$ (64,440)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		548	6,573	(1,026)	8,411
Amortization of actuarial losses and prior service cost		(2,407)	(1,830)	(4,855)	(3,430)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax		2,460	1,882	4,960	3,534
Unrealized Gains on Investment Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), before Tax		(26,167)		(26,167)			(72,707)
Deferred tax expense (benefit)		(9,519)		(9,519)			(26,832)
Accumulated other comprehensive income (loss), net of tax	[1]	(16,648)	31,213	(16,648)	31,213	(23,183)	(45,875)	24,034	(15,125)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	2,111	7,736	2,096	10,594
Funded Status of Defined Benefit Plan
Accumulated Other Comprehensive Income (Loss), before Tax		(136,814)		(136,814)			(141,774)
Deferred tax expense (benefit)		(50,619)		(50,619)			(52,457)
Accumulated other comprehensive income (loss), net of tax	[1]	(86,195)	(46,240)	(86,195)	(46,240)	(87,758)	(89,317)	(47,403)	(48,423)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	(1,563)	(1,163)	(3,122)	(2,183)
Unrealized Loss on Cash Flow Hedges
Accumulated other comprehensive income (loss), net of tax	[1]	0	0	0	0	$ 0	$ 0	$ (455)	$ (892)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	$ 0	$ 0	$ 0	$ 0

[1] All amounts are net of tax.