Other Comprehensive Income (Loss) (Component Of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	$ 0	$ 0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), before Reclassification, after Tax	125	(483)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, before Reclassification Adjustments, after Tax	(13,597)	18,176
Other comprehensive loss before reclassifications	(13,472)	17,693
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax	125	(483)
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax	(13,597)	18,176
Other comprehensive income (loss)	(13,472)	17,693
Changes in pension plan assets and benefit obligations, Net-of-tax amount	(34,421)	(26,674)	$ 34,421	$ 26,674
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	(573)	(937)	(698)	(454)
Unrealized gains on available-for-sale securities, Net-of-tax amount	27,093	35,715	40,690	17,539
Total accumulated other comprehensive income (loss), Net-of-tax amount	$ (7,901)	$ 8,104	$ 5,571	$ (9,589)