Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Income before income taxes	$ 23,386	$ 37,026	$ 29,679
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	(6,245)	(2,283)	5,532
Less: reclassification adjustment for net gains on sales realized in net income, Before Tax Amount	(518)	(1,265)	(635)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Before Tax Amount	0	5	0
Total net unrealized gains (losses) on available-for-sale investment securities, Before Tax Amount	(6,763)	(3,543)	4,897
Cash flow hedge derivative, Before Tax Amount
Net change in fair value of interest rate swap, Before Tax Amount	(86)	(574)	(307)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Before Tax Amount	308	377	66
Total cash flow hedge derivative, Before Tax Amount	222	(197)	(241)
Defined benefit pension plans, Before Tax Amount
Net unrealized (losses) gains arising during the period, Before Tax Amount	(155)	(797)	(11,968)
Less: amortization of net actuarial loss included in net periodic pension costs, Before Tax Amount	1,321	1,362	666
Less: accretion of prior service cost included in net periodic pension costs, Before Tax Amount	(283)	(280)	(288)
Less: reclassification adjustment for net losses realized in net income	1,434	0	0
Total defined benefit pension plans, Before Tax Amount	2,317	285	(11,590)
Other comprehensive income (loss), Before Tax Amount	(4,224)	(3,455)	(6,934)
Total comprehensive income (loss), Before Tax Amount	19,162	33,571	22,745
Income taxes	3,881	9,758	7,448
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)	(2,186)	(799)	1,936
Less: reclassification adjustment for net gains on sales realized in net income, Tax Expense (Benefit)	(181)	(443)	(222)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Tax Expense (Benefit)	0	2	0
Total net unrealized gains (losses) on available-for-sale investment securities, Tax Expense (Benefit)	(2,367)	(1,240)	1,714
Cash flow hedge derivative, Tax Expense (Benefit)
Net change in fair value of interest rate swap, Tax Expense (Benefit)	(30)	(201)	(107)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Tax Expense (Benefit)	108	132	23
Total cash flow hedge derivative, Tax Expense (Benefit)	78	(69)	(84)
Defined benefit pension plans, Tax Expense (Benefit)
Net unrealized (losses) gains arising during the period, Tax Expense (Benefit)	(54)	(279)	(4,189)
Less: amortization of net actuarial loss included in net periodic pension costs, Tax Expense (Benefit)	462	477	233
Less: accretion of prior service cost included in net periodic pension costs, Tax Expense (Benefit)	(99)	(98)	(101)
Less: reclassification adjustment for net losses realized in net income, Tax Expense (Benefit)	502	0	0
Total defined benefit pension plans, Tax Expense (Benefit)	811	100	(4,057)
Other comprehensive income (loss), Tax Expense (Benefit)	(1,478)	(1,209)	(2,427)
Total comprehensive income (loss), Tax Expense (Benefit)	2,403	8,549	5,021
Net income	19,505	27,268	22,231
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	(4,059)	(1,484)	3,596
Less: reclassification adjustment for net gains on sales realized in net income, Net of Tax Amount	(337)	(822)	(413)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Net of Tax Amount	0	3	0
Total net unrealized gains (losses) on available-for-sale investment securities, Net of Tax Amount	(4,396)	(2,303)	3,183
Cash flow hedge derivative, Net of Tax Amount
Net change in fair value of interest rate swap, Net of Tax Amount	(56)	(373)	(200)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Net of Tax Amount	200	245	43
Total cash flow hedge derivative, Net of Tax Amount	144	(128)	(157)
Defined benefit pension plans, Net of Tax Amount
Net unrealized (losses) gains arising during the period, Net of Tax Amount	(101)	(518)	(7,779)
Less: amortization of net actuarial loss included in net periodic pension costs, Net of Tax Amount	859	885	433
Less: accretion of prior service cost included in net periodic pension costs, Net of Tax Amount	(184)	(182)	(187)
Less: Reclassification adjustment for net losses realized in net income, Net of Tax Amount	932	0	0
Total defined benefit pension plans, Net of Tax Amount	1,506	185	(7,533)
Other comprehensive income (loss), Net of Tax Amount	(2,746)	(2,246)	(4,507)
Total comprehensive income (loss), Net of Tax Amount	$ 16,759	$ 25,022	$ 17,724