Summary of Significant Accounting Policies (Components Of Other Comprehensive Income (Loss) And Related Tax Effects) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in net unrealized holding gains (losses) on available-for-sale securities:
Change arising during the period		$ 14,156	$ (18,891)	$ (236)
Reclassification adjustment for losses (gains) included in net income	[1]	(14)	10,406	1,867
Change in net unrealized holding gains (losses) on available-for-sale securities		14,142	(8,485)	1,631
Tax effect		4,242	(2,569)	685
Total		9,900	(5,916)	946
Change in funded status of pension plan:
Unrecognized net gain (loss) arising during the period		3,173	(4,316)	1,700
Amortization of net actuarial loss included in net pension expense	[2]	352		18
Total		3,525	(4,316)	1,718
Tax effect		1,083	(1,312)	514
Total		2,442	(3,004)	1,204
Change in unrealized loss on derivative instruments:
Amount of loss recognized during the period		(4,116)	(1,607)
Reclassification adjustment for net interest expense included in net income	[3]	827	477
Change in unrealized loss on derivative instruments		(3,289)	(1,130)
Tax effect		(982)	(341)
Total		(2,307)	(789)
Other comprehensive income (loss)		$ 10,035	$ (9,709)	$ 2,150

[1] Represents net realized gains and losses arising from the sale of available-for-sale securities. These net realized gains and losses are included in the consolidated statements of income in the line item “Net gains (losses) on sales of securities.” See “Note B – Investment Securities” for the income tax expense or benefit related to these net realized gains and losses, which is included in the consolidated statements of income in the line item “Income tax expense.”

[2] Represents the amortization of net actuarial loss relating to the Corporation’s defined benefit pension plan. This item is a component of net periodic pension cost (see “Note J – Retirement Plans”) and included in the consolidated statements of income in the line item “Other noninterest income.”

[3] Represents the net interest expense recorded on derivative transactions and included in the consolidated statements of income under “Interest expense.”