Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Income before income taxes	$ 29,679	$ 26,885	$ 26,423
Net unrealized gains (losses) on available-for-sale investment securities, Before Tax Amount
Net unrealized holding gains (losses) arising during the period, Before Tax Amount	5,532	(11,712)	1,888
Less: reclassification adjustment for net gains on sales realized in net income, Before Tax Amount	(635)	(3,389)	(305)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Before Tax Amount	0	0	13
Total net unrealized gains (losses) on available-for-sale investment securities, Before Tax Amount	4,897	(15,101)	1,596
Cash flow hedge derivative, Before Tax Amount
Net change in fair value of interest rate swap, Before Tax Amount	(241)	43	(474)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Before Tax Amount	0	1,866	0
Total cash flow hedge derivative, Before Tax Amount	(241)	1,909	(474)
Defined benefit pension plans, Before Tax Amount
Net unrealized (losses) gains arising during the period, Before Tax Amount	(11,968)	7,496	(3,297)
Less: amortization of net actuarial loss included in net periodic pension costs, Before Tax Amount	666	1,282	1,170
Less: accretion of prior service cost included in net periodic pension costs, Before Tax Amount	(288)	(255)	(255)
Total defined benefit pension plans, Before Tax Amount	(11,590)	8,523	(2,382)
Other comprehensive income (loss), Before Tax Amount	(6,934)	(4,669)	(1,260)
Total comprehensive income (loss), Before Tax Amount	22,745	22,216	25,163
Income taxes	7,448	5,696	5,551
Net unrealized gains (losses) on available-for-sale investment securities, Tax Expense (Benefit)
Net unrealized holding gains (losses) arising during the period, Tax Expense (Benefit)	1,936	(4,099)	660
Less: reclassification adjustment for net gains on sales realized in net income, Tax Expense (Benefit)	(222)	(1,186)	(107)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Tax Expense (Benefit)	0	0	5
Total net unrealized gains (losses) on available-for-sale investment securities, Tax Expense (Benefit)	1,714	(5,285)	558
Cash flow hedge derivative, Tax Expense (Benefit)
Net change in fair value of interest rate swap, Tax Expense (Benefit)	(84)	15	(165)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Tax Expense (Benefit)	0	653	0
Total cash flow hedge derivative, Tax Expense (Benefit)	(84)	668	(165)
Defined benefit pension plans, Tax Expense (Benefit)
Net unrealized (losses) gains arising during the period, Tax Expense (Benefit)	(4,189)	2,623	(1,154)
Less: amortization of net actuarial loss included in net periodic pension costs, Tax Expense (Benefit)	233	449	409
Less: accretion of prior service cost included in net periodic pension costs, Tax Expense (Benefit)	(101)	(89)	(89)
Total defined benefit pension plans, Tax Expense (Benefit)	(4,057)	2,983	(834)
Other comprehensive income (loss), Tax Expense (Benefit)	(2,427)	(1,634)	(441)
Total comprehensive income (loss), Tax Expense (Benefit)	5,021	4,062	5,110
Net income	22,231	21,189	20,872
Net unrealized gains (losses) on available-for-sale investment securities, Net of Tax Amount
Net unrealized holding gains (losses) arising during the period, Net of Tax Amount	3,596	(7,613)	1,228
Less: reclassification adjustment for net gains on sales realized in net income, Net of Tax Amount	(413)	(2,203)	(198)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Net of Tax Amount	0	0	8
Total net unrealized gains (losses) on available-for-sale investment securities, Net of Tax Amount	3,183	(9,816)	1,038
Cash flow hedge derivative, Net of Tax Amount
Net change in fair value of interest rate swap, Net of Tax Amount	(157)	28	(309)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Net of Tax Amount	0	1,213	0
Total cash flow hedge derivative, Net of Tax Amount	(157)	1,241	(309)
Defined benefit pension plans, Net of Tax Amount
Net unrealized (losses) gains arising during the period, Net of Tax Amount	(7,779)	4,873	(2,143)
Less: amortization of net actuarial loss included in net periodic pension costs, Net of Tax Amount	433	833	761
Less: accretion of prior service cost included in net periodic pension costs, Net of Tax Amount	(187)	(166)	(166)
Total defined benefit pension plans, Net of Tax Amount	(7,533)	5,540	(1,548)
Other comprehensive income (loss), Net of Tax Amount	(4,507)	(3,035)	(819)
Total comprehensive income (loss), Net of Tax Amount	$ 17,724	$ 18,154	$ 20,053