Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Income before income taxes	$ 37,026	$ 29,679	$ 26,885
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	(2,283)	5,532	(11,712)
Less: reclassification adjustment for net gains on sales realized in net income, Before Tax Amount	(1,265)	(635)	(3,389)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Before Tax Amount	5	0	0
Total net unrealized gains (losses) on available-for-sale investment securities, Before Tax Amount	(3,543)	4,897	(15,101)
Cash flow hedge derivative, Before Tax Amount
Net change in fair value of interest rate swap, Before Tax Amount	(197)	(241)	43
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Before Tax Amount	0	0	1,866
Total cash flow hedge derivative, Before Tax Amount	(197)	(241)	1,909
Defined benefit pension plans, Before Tax Amount
Net unrealized (losses) gains arising during the period, Before Tax Amount	(797)	(11,968)	7,496
Less: amortization of net actuarial loss included in net periodic pension costs, Before Tax Amount	1,362	666	1,282
Less: accretion of prior service cost included in net periodic pension costs, Before Tax Amount	(280)	(288)	(255)
Total defined benefit pension plans, Before Tax Amount	285	(11,590)	8,523
Other comprehensive income (loss), Before Tax Amount	(3,455)	(6,934)	(4,669)
Total comprehensive income (loss), Before Tax Amount	33,571	22,745	22,216
Income taxes	9,758	7,448	5,696
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)	(799)	1,936	(4,099)
Less: reclassification adjustment for net gains on sales realized in net income, Tax Expense (Benefit)	(443)	(222)	(1,186)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Tax Expense (Benefit)	2	0	0
Total net unrealized gains (losses) on available-for-sale investment securities, Tax Expense (Benefit)	(1,240)	1,714	(5,285)
Cash flow hedge derivative, Tax Expense (Benefit)
Net change in fair value of interest rate swap, Tax Expense (Benefit)	(69)	(84)	15
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Tax Expense (Benefit)	0	0	653
Total cash flow hedge derivative, Tax Expense (Benefit)	(69)	(84)	668
Defined benefit pension plans, Tax Expense (Benefit)
Net unrealized (losses) gains arising during the period, Tax Expense (Benefit)	(279)	(4,189)	2,623
Less: amortization of net actuarial loss included in net periodic pension costs, Tax Expense (Benefit)	477	233	449
Less: accretion of prior service cost included in net periodic pension costs, Tax Expense (Benefit)	(98)	(101)	(89)
Total defined benefit pension plans, Tax Expense (Benefit)	100	(4,057)	2,983
Other comprehensive income (loss), Tax Expense (Benefit)	(1,209)	(2,427)	(1,634)
Total comprehensive income (loss), Tax Expense (Benefit)	8,549	5,021	4,062
Net income	27,268	22,231	21,189
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	(1,484)	3,596	(7,613)
Less: reclassification adjustment for net gains on sales realized in net income, Net of Tax Amount	(822)	(413)	(2,203)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Net of Tax Amount	3	0	0
Total net unrealized gains (losses) on available-for-sale investment securities, Net of Tax Amount	(2,303)	3,183	(9,816)
Cash flow hedge derivative, Net of Tax Amount
Net change in fair value of interest rate swap, Net of Tax Amount	(128)	(157)	28
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Net of Tax Amount	0	0	1,213
Total cash flow hedge derivative, Net of Tax Amount	(128)	(157)	1,241
Defined benefit pension plans, Net of Tax Amount
Net unrealized (losses) gains arising during the period, Net of Tax Amount	(518)	(7,779)	4,873
Less: amortization of net actuarial loss included in net periodic pension costs, Net of Tax Amount	885	433	833
Less: accretion of prior service cost included in net periodic pension costs, Net of Tax Amount	(182)	(187)	(166)
Total defined benefit pension plans, Net of Tax Amount	185	(7,533)	5,540
Other comprehensive income (loss), Net of Tax Amount	(2,246)	(4,507)	(3,035)
Total comprehensive income (loss), Net of Tax Amount	$ 25,022	$ 17,724	$ 18,154