Accumulated Other Comprehensive Loss (Schedule Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), before Tax		$ (214,481)	$ (104,352)
Long-term obligations		944,675	924,905		$ 710,097
Deferred tax expense (benefit)		(79,289)	(39,912)
Accumulated other comprehensive income (loss), net of tax		(135,192)	(64,440)		(52,981)
Income taxes		(125,585)	(122,028)		(65,032)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	12,351	81
Securities gains (losses)		26,673	10,817		29,096
Unrealized Gains on Investment Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), before Tax		(72,707)	(24,504)
Deferred tax expense (benefit)		(26,832)	(9,379)
Accumulated other comprehensive income (loss), net of tax	[2]	(45,875)	(15,125)		5,098
Income taxes	[1]	(9,869)	(4,138)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1],[2]	16,804	6,679
Securities gains (losses)	[1]	26,673	10,817
Funded Status of Defined Benefit Plan
Accumulated Other Comprehensive Income (Loss), before Tax		(141,774)	(78,419)
Deferred tax expense (benefit)		(52,457)	(29,996)
Accumulated other comprehensive income (loss), net of tax	[2]	(89,317)	(48,423)		(55,415)
Income taxes	[1]	2,616	4,988
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1],[2]	(4,453)	(6,598)
Employee Benefits, prior service costs	[1]	(210)	(210)
Reclassification adjustment for losses included in income before income taxes	[1]	(6,859)	(11,376)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax		(7,069)	(11,586)	[1]
Unrealized Loss on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), before Tax		0	(1,429)
Deferred tax expense (benefit)		0	(537)
Accumulated other comprehensive income (loss), net of tax	[2]	0	(892)		$ (2,664)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[2]	$ 0	$ 0

[1] Amounts in parentheses indicate debits to profit/loss.

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