Other Comprehensive Income (Loss) (Component Of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax			$ 2,562
Other comprehensive loss before reclassifications	$ (5,141)	$ 707	(30,919)	$ 4,740
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	0	0	(3,175)	0
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, before Tax	0	0	(2,024)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0	(2,024)	0
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax	(5,141)	707		4,740
Other comprehensive income (loss)	(5,141)	707	(28,895)	4,740
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments, after Tax	(5,141)	707	(30,919)	4,740
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax		0	0	0
Changes in pension plan assets and benefit obligations, Net-of-tax amount	(26,701)	(14,740)	(26,701)	(14,740)	$ 26,701	$ 23,526	$ 14,740	$ 14,740
Unrealized gains on available-for-sale securities, Net-of-tax amount	(33,449)	1,735	(33,449)	1,735	(28,308)	(2,928)	1,028	(3,005)
Total accumulated other comprehensive income (loss), Net-of-tax amount	$ (60,150)	$ (13,005)	(60,150)	(13,005)	$ (55,009)	(26,454)	$ (13,712)	$ (17,745)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, before Tax				$ 0
Accumulated Other Comprehensive Income (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets						(3,806)
Accumulated Other Comprehensive Income (loss) [Member] | Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets						(3,175)
Accumulated Other Comprehensive Income (loss) [Member] | Debt Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets						(631)
Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss)			(33,696)
Accounting Standards Update 2016-01 [Member] | Debt Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax			$ (30,521)
Accounting Standards Update 2016-01 [Member] | Accumulated Other Comprehensive Income (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets						$ (995)