Accumulated Other Comprehensive Income (Loss) (Schedule Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), before Tax		$ (175,861)		$ (214,481)
Deferred tax expense (benefit)		(64,920)		(79,289)
Accumulated other comprehensive income (loss), net of tax		(110,941)	$ (23,824)	(135,192)	$ (64,440)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(1,574)	1,838
Amortization of actuarial losses and prior service cost		(2,234)	(1,600)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax		2,500	1,652
Unrealized Gains on Investment Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), before Tax		(36,587)		(72,707)
Deferred tax expense (benefit)		(13,404)		(26,832)
Accumulated other comprehensive income (loss), net of tax	[1]	(23,183)	24,034	(45,875)	(15,125)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	(15)	2,858
Funded Status of Defined Benefit Plan
Accumulated Other Comprehensive Income (Loss), before Tax		(139,274)		(141,774)
Deferred tax expense (benefit)		(51,516)		(52,457)
Accumulated other comprehensive income (loss), net of tax	[1]	(87,758)	(47,403)	(89,317)	(48,423)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	(1,559)	(1,020)
Unrealized Loss on Cash Flow Hedges
Accumulated other comprehensive income (loss), net of tax	[1]	0	(455)	$ 0	$ (892)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	$ 0	$ 0

[1] All amounts are net of tax.