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, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain (loss) on investment securities		$ 1,677	$ (127)	$ 1,260
Interest income		129,912	122,864	112,615
Income before income taxes		59,421	49,532	43,471
Income tax (expense) benefit		(10,559)	(10,006)	(9,945)
Net income		48,862	39,526	33,526
Total reclassified for the period		(177)	(910)	(7)
Securities Available for Sale and Transferred Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification before tax	[1]	1,176	(539)	1,103
Reclassification tax	[1]	(307)	136	(426)
Total reclassified for the period	[1]	869	(403)	677
Prior Service Credit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification before tax	[2]	65	72
Net Actuarial Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification before tax	[2]	(1,463)	(750)
Pension And Post-Retirement Obligations [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification before tax		(1,398)	(678)
Reclassification tax		352	171
Total reclassified for the period		(1,046)	(507)	$ (684)
Reclassification out of Accumulated Other Comprehensive Income | Securities Available for Sale and Transferred Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net gain (loss) on investment securities		1,677	(127)
Interest income		(501)	(412)
Income before income taxes		1,176	(539)
Income tax (expense) benefit		(307)	136
Net income		$ 869	$ (403)

[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 19 – Employee Benefit Plans for additional information.