Accumulated Other Comprehensive Income (Loss) (Amounts Reclassified Out of Each Component of Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain (loss) on investment securities		$ 1,599	$ 1,677	$ (127)
Interest income		138,985	129,912	122,864
Income before income taxes		45,723	59,421	49,532
Income tax (expense) benefit		(7,391)	(10,559)	(10,006)
Net income		38,332	48,862	39,526
Total reclassified for the period		19	(177)	(910)
Securities Available for Sale and Transferred Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification before tax	[1]	1,281	1,176	(539)
Reclassification tax	[1]	(329)	(307)	136
Total reclassified for the period	[1]	952	869	(403)
Prior Service Credit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification before tax	[2]	34	65
Net Actuarial Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification before tax	[2]	(1,288)	(1,463)
Pension And Post-Retirement Obligations [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification before tax		(1,254)	(1,398)
Reclassification tax		321	352
Total reclassified for the period		(933)	(1,046)	$ (507)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Securities Available for Sale and Transferred Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain (loss) on investment securities		1,599	1,677
Interest income		(318)	(501)
Income before income taxes		1,281	1,176
Income tax (expense) benefit		(329)	(307)
Net income		$ 952	$ 869

[1] Includes amounts related to the amortization/accretion of unrealized net gains and losses related to the Company’s reclassification of available for sale investment securities to the held to maturity category. The unrealized net gains/losses will be amortized/accreted over the remaining life of the investment securities as an adjustment of yield.

[2] These items are included in the computation of net periodic pension expense. See Note 21 – Employee Benefit Plans for additional information.