Other Comprehensive Income (Loss) (Component Of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before reclassifications	$ 318,000	$ 13,840,000	$ 26,385,000	$ 36,841,000
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax			0	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	111,000	(49,000)	(357,000)	(556,000)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax	228,000	13,742,000	24,146,000	37,730,000
Other comprehensive income (loss)	339,000	13,693,000	23,789,000	37,174,000
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments, after Tax	207,000	13,889,000	26,742,000	37,397,000
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	0	0	0	0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax	111,000	(49,000)	(357,000)	(556,000)
Changes in pension plan assets and benefit obligations, Net-of-tax amount	(26,674,000)	(29,672,000)	(26,674,000)	(29,672,000)	$ 26,674,000	$ 26,674,000	$ 29,672,000	$ 29,672,000
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	(811,000)	(556,000)	(811,000)	(556,000)	(922,000)	(454,000)	(507,000)	0
Unrealized gains on available-for-sale securities, Net-of-tax amount	41,685,000	17,614,000	41,685,000	17,614,000	41,457,000	17,539,000	3,872,000	(20,116,000)
Total accumulated other comprehensive income (loss), Net-of-tax amount	14,200,000	(12,614,000)	14,200,000	(12,614,000)	$ 13,861,000	$ (9,589,000)	$ (26,307,000)	$ (49,788,000)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Net of Tax	21,000	(147,000)	(2,596,000)	333,000
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(21,000)	(147,000)	2,596,000	(333,000)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	$ 27,000	$ 186,000	$ (3,300,000)	421,000
OCI, Debt Securities, Available-for-Sale, Transfer from Held-to-Maturity, Gain (Loss), before Adjustment and Tax				$ 24,200,000