Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Income, Before Tax Amount	$ 7,286	$ 8,758	$ 17,375	$ 17,008
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	2,084	(3,555)	4,302	(1,397)
Less: reclassification adjustment for net gains on sales realized in net income, Before Tax Amount	(413)	(181)	(457)	(272)
Total net unrealized gains on available-for-sale investment securities, Before Tax Amount	1,671	(3,736)	3,845	(1,669)
Cash flow hedge derivative, Before Tax Amount
Net change in fair value of interest rate swap, Before Tax Amount	(220)	377	(765)	40
Defined benefit pension plans, Before Tax Amount
Amortization of net actuarial loss included in net periodic pension costs, Before Tax Amount	329	340	658	681
Accretion of prior service cost included in net periodic pension costs, Before Tax Amount	(70)	(70)	(141)	(140)
Total defined benefit pension plans, Before Tax Amount	259	270	517	541
Other comprehensive income (loss), Before Tax Amount	1,710	(3,089)	3,597	(1,088)
Total comprehensive income (loss), Before Tax Amount	8,996	5,669	20,972	15,920
Tax (expense) benefit	2,046	2,292	4,846	4,426
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)	730	(1,244)	1,506	(489)
Less: reclassification adjustment for net gains on sales realized in net income, Tax Expense (Benefit)	(145)	(63)	(160)	(95)
Total net unrealized gains on available-for-sale investment securities, Tax Expense (Benefit)	585	(1,307)	1,346	(584)
Cash flow hedge derivative, Tax Expense (Benefit)
Net change in fair value of interest rate swap, Tax Expense (Benefit)	(77)	132	(268)	14
Defined benefit pension plans, Tax Expense (Benefit)
Amortization of net actuarial loss included in net periodic pension costs, Tax Expense (Benefit)	115	119	230	239
Accretion of prior service cost included in net periodic pension costs, Tax Expense (Benefit)	(24)	(25)	(49)	(49)
Total defined benefit pension plans, Tax Expense (Benefit)	91	94	181	190
Other comprehensive income (loss), Tax Expense (Benefit)	599	(1,081)	1,259	(380)
Total comprehensive income (loss), Tax Expense (Benefit)	2,645	1,211	6,105	4,046
Net income	5,240	6,466	12,529	12,582
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	1,354	(2,311)	2,796	(908)
Less: reclassification adjustment for net gains on sales realized in net income, Net of Tax Amount	(268)	(118)	(297)	(177)
Total net unrealized gains on available-for-sale investment securities, Net of Tax Amount	1,086	(2,429)	2,499	(1,085)
Cash flow hedge derivative, Net of Tax Amount
Net change in fair value of interest rate swap, Net of Tax Amount	(143)	245	(497)	26
Defined benefit pension plans, Net of Tax Amount
Amortization of net actuarial loss included in net periodic pension costs, Net of Tax Amount	214	221	428	442
Accretion of prior service cost included in net periodic pension costs, Net of Tax Amount	(46)	(45)	(92)	(91)
Total defined benefit pension plans, Net of Tax Amount	168	176	336	351
Other comprehensive income (loss), Net of Tax Amount	1,111	(2,008)	2,338	(708)
Total comprehensive income (loss), Net of Tax Amount	$ 6,351	$ 4,458	$ 14,867	$ 11,874