Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Income, Before Tax Amount	$ 8,758	$ 6,627	$ 17,008	$ 14,358
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	(3,555)	2,708	(1,397)	5,458
Less: reclassification adjustment for net gains on sales realized in net income, Before Tax Amount	(181)	(415)	(272)	(557)
Total net unrealized gains on available-for-sale investment securities, Before Tax Amount	(3,736)	2,293	(1,669)	4,901
Cash flow hedge derivative, Before Tax Amount
Net change in fair value of interest rate swap, Before Tax Amount	377	0	40	0
Defined benefit pension plans, Before Tax Amount
Amortization of net actuarial loss included in net periodic pension costs, Before Tax Amount	340	167	681	331
Accretion of prior service cost included in net periodic pension costs, Before Tax Amount	(70)	(69)	(140)	(144)
Total defined benefit pension plans, Before Tax Amount	270	98	541	187
Other comprehensive income (loss), Before Tax Amount	(3,089)	2,391	(1,088)	5,088
Total comprehensive income (loss), Before Tax Amount	5,669	9,018	15,920	19,446
Tax (expense) benefit	2,292	1,547	4,426	3,552
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)	(1,244)	948	(489)	1,911
Less: reclassification adjustment for net gains on sales realized in net income, Tax Expense (Benefit)	(63)	(145)	(95)	(195)
Total net unrealized gains on available-for-sale investment securities, Tax Expense (Benefit)	(1,307)	803	(584)	1,716
Cash flow hedge derivative, Tax Expense (Benefit)
Net change in fair value of interest rate swap, Tax Expense (Benefit)	132	0	14	0
Defined benefit pension plans, Tax Expense (Benefit)
Amortization of net actuarial loss included in net periodic pension costs, Tax Expense (Benefit)	119	59	239	116
Accretion of prior service cost included in net periodic pension costs, Tax Expense (Benefit)	(25)	(25)	(49)	(51)
Total defined benefit pension plans, Tax Expense (Benefit)	94	34	190	65
Other comprehensive income (loss), Tax Expense (Benefit)	(1,081)	837	(380)	1,781
Total comprehensive income (loss), Tax Expense (Benefit)	1,211	2,384	4,046	5,333
Net income	6,466	5,080	12,582	10,806
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	(2,311)	1,760	(908)	3,547
Less: reclassification adjustment for net gains on sales realized in net income, Net of Tax Amount	(118)	(270)	(177)	(362)
Total net unrealized gains on available-for-sale investment securities, Net of Tax Amount	(2,429)	1,490	(1,085)	3,185
Cash flow hedge derivative, Net of Tax Amount
Net change in fair value of interest rate swap, Net of Tax Amount	245	0	26	0
Defined benefit pension plans, Net of Tax Amount
Amortization of net actuarial loss included in net periodic pension costs, Net of Tax Amount	221	108	442	215
Accretion of prior service cost included in net periodic pension costs, Net of Tax Amount	(45)	(44)	(91)	(93)
Total defined benefit pension plans, Net of Tax Amount	176	64	351	122
Other comprehensive income (loss), Net of Tax Amount	(2,008)	1,554	(708)	3,307
Total comprehensive income (loss), Net of Tax Amount	$ 4,458	$ 6,634	$ 11,874	$ 14,113