Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Income, Before Tax Amount	$ 10,307	$ 8,499	$ 27,315	$ 22,857
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	797	(486)	(600)	4,972
Less: reclassification adjustment for net gains on sales realized in net income, Before Tax Amount	(296)	0	(568)	(557)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Before Tax Amount	5	0	5	0
Total net unrealized gains on available-for-sale investment securities, Before Tax Amount	506	(486)	(1,163)	4,415
Cash flow hedge derivative, Before Tax Amount
Net change in fair value of interest rate swap, Before Tax Amount	(483)	0	(443)	0
Defined benefit pension plans, Before Tax Amount
Amortization of net actuarial loss included in net periodic pension costs, Before Tax Amount	341	168	1,022	499
Accretion of prior service cost included in net periodic pension costs, Before Tax Amount	(70)	(72)	(210)	(216)
Total defined benefit pension plans, Before Tax Amount	271	96	812	283
Other comprehensive income (loss), Before Tax Amount	294	(390)	(794)	4,698
Total comprehensive income (loss), Before Tax Amount	10,601	8,109	26,521	27,555
Tax (expense) benefit	2,779	2,264	7,205	5,816
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)	279	(170)	(210)	1,741
Less: reclassification adjustment for net gains on sales realized in net income, Tax Expense (Benefit)	(104)	0	(199)	(195)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Tax Expense (Benefit)	2	0	2	0
Total net unrealized gains on available-for-sale investment securities, Tax Expense (Benefit)	177	(170)	(407)	1,546
Cash flow hedge derivative, Tax Expense (Benefit)
Net change in fair value of interest rate swap, Tax Expense (Benefit)	(169)	0	(155)	0
Defined benefit pension plans, Tax Expense (Benefit)
Amortization of net actuarial loss included in net periodic pension costs, Tax Expense (Benefit)	119	59	358	175
Accretion of prior service cost included in net periodic pension costs, Tax Expense (Benefit)	(24)	(26)	(73)	(77)
Total defined benefit pension plans, Tax Expense (Benefit)	95	33	285	98
Other comprehensive income (loss), Tax Expense (Benefit)	103	(137)	(277)	1,644
Total comprehensive income (loss), Tax Expense (Benefit)	2,882	2,127	6,928	7,460
Net income	7,528	6,235	20,110	17,041
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	518	(316)	(390)	3,231
Less: reclassification adjustment for net gains on sales realized in net income, Net of Tax Amount	(192)	0	(369)	(362)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Net of Tax Amount	3	0	3	0
Total net unrealized gains on available-for-sale investment securities, Net of Tax Amount	329	(316)	(756)	2,869
Cash flow hedge derivative, Net of Tax Amount
Net change in fair value of interest rate swap, Net of Tax Amount	(314)	0	(288)	0
Defined benefit pension plans, Net of Tax Amount
Amortization of net actuarial loss included in net periodic pension costs, Net of Tax Amount	222	109	664	324
Accretion of prior service cost included in net periodic pension costs, Net of Tax Amount	(46)	(46)	(137)	(139)
Total defined benefit pension plans, Net of Tax Amount	176	63	527	185
Other comprehensive income (loss), Net of Tax Amount	191	(253)	(517)	3,054
Total comprehensive income (loss), Net of Tax Amount	$ 7,719	$ 5,982	$ 19,593	$ 20,095