Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income	$ 20,872	$ 18,882	$ 15,756
Before Tax Amount
Net income	26,423	23,658	19,038
Net unrealized gains (losses) on available-for-sale investment securities:
Net unrealized holding gains (losses) arising during the period	1,888	11,282	(6,535)
Less: reclassification adjustment for net gains on sales realized in net income	(305)	(1,417)	(432)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income	13	16	62
Total net unrealized gains (losses) on available-for-sale investment securities	1,596	9,881	(6,905)
Net change in fair value of derivatives used for cash flow hedges	(474)	(1,926)	(1,277)
Defined benefit pension plans:
Net unrealized losses arising during the period	(3,297)	(7,418)	(1,858)
Less: amortization of net loss included in net periodic pension costs	1,170	743	693
Less: accretion of prior service cost included in net periodic pension costs	(255)	(255)	(256)
Total defined benefit pension plans	(2,382)	(6,930)	(1,421)
Other comprehensive (loss) income	(1,260)	1,025	(9,603)
Total comprehensive income	25,163	24,683	9,435
Tax Expense (Benefit)
Net income	5,551	4,776	3,282
Net unrealized gains (losses) on available-for-sale investment securities:
Net unrealized holding gains (losses) arising during the period	660	3,949	(2,287)
Less: reclassification adjustment for net gains on sales realized in net income	(107)	(496)	(151)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income	5	6	22
Total net unrealized gains (losses) on available-for-sale investment securities	558	3,459	(2,416)
Net change in fair value of derivatives used for cash flow hedges	(165)	(674)	(447)
Defined benefit pension plans:
Net unrealized losses arising during the period	(1,154)	(2,596)	(650)
Less: amortization of net loss included in net periodic pension costs	409	260	243
Less: accretion of prior service cost included in net periodic pension costs	(89)	(89)	(91)
Total defined benefit pension plans	(834)	(2,425)	(498)
Other comprehensive (loss) income	(441)	360	(3,361)
Total comprehensive income	5,110	5,136	(79)
Net of Tax Amount
Net income	20,872	18,882	15,756
Net unrealized gains (losses) on available-for-sale investment securities:
Net unrealized holding gains (losses) arising during the period	1,228	7,333	(4,248)
Less: reclassification adjustment for net gains on sales realized in net income	(198)	(921)	(281)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income	8	10	40
Total net unrealized gains (losses) on available-for-sale investment securities	1,038	6,422	(4,489)
Net change in fair value of derivatives used for cash flow hedges	(309)	(1,252)	(830)
Defined benefit pension plans:
Net unrealized losses arising during the period	(2,143)	(4,822)	(1,208)
Less: amortization of net loss included in net periodic pension costs	761	483	450
Less: accretion of prior service cost included in net periodic pension costs	(166)	(166)	(165)
Total defined benefit pension plans	(1,548)	(4,505)	(923)
Other comprehensive (loss) income	(819)	665	(6,242)
Total comprehensive income	$ 20,053	$ 19,547	$ 9,514