Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement Of Income And Comprehensive Income [Abstract]
Income, Before Tax Amount	$ 7,439	$ 7,612	$ 20,914	$ 19,989
Net unrealized (losses) gains on available-for-sale investment securities, Before Tax Amount
Net unrealized holding (losses) gains arising during the period, Before Tax Amount	442	2,698	(10,163)	3,215
Less: reclassification adjustment for net gains on sales realized in net income, Before Tax Amount	(1,426)	(9)	(2,950)	(291)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Before Tax Amount		4		13
Total net unrealized (losses) gains on available-for-sale investment securities, Before Tax Amount	(984)	2,693	(13,113)	2,937
Cash flow hedge derivative, Before Tax Amount
Net change in fair value of interest rate swap, Before Tax Amount		(213)	43	(602)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Before Tax Amount			1,866
Total cash flow hedge derivative, Before Tax Amount		(213)	1,909	(602)
Defined benefit pension plans, Before Tax Amount
Less: amortization of net loss included in net periodic pension costs, Before Tax Amount	320	293	961	882
Less: accretion of prior service cost included in net periodic pension costs, Before Tax Amount	(64)	(64)	(191)	(192)
Total defined benefit pension plans, Before Tax Amount	256	229	770	690
Other comprehensive (loss) income, Before Tax Amount	(728)	2,709	(10,434)	3,025
Total comprehensive income, Before Tax Amount	6,711	10,321	10,480	23,014
Income, Tax Expense (Benefit)	1,400	1,842	4,647	4,193
Net unrealized (losses) gains on available-for-sale investment securities, Tax Expense (Benefit)
Net unrealized holding (losses) gains arising during the period, Tax Expense (Benefit)	155	944	(3,557)	1,125
Less: reclassification adjustment for net gains on sales realized in net income, Tax Expense (Benefit)	(499)	(3)	(1,032)	(102)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Tax Expense (Benefit)		2		5
Total net unrealized (losses) gains on available-for-sale investment securities, Tax Expense (Benefit)	(344)	943	(4,589)	1,028
Cash flow hedge derivative, Tax Expense (Benefit)
Net change in fair value of interest rate swap, Tax Expense (Benefit)		(75)	15	(211)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Tax Expense (Benefit)			653
Total cash flow hedge derivative, Tax Expense (Benefit)		(75)	668	(211)
Defined benefit pension plans, Tax Expense (Benefit)
Less: amortization of net loss included in net periodic pension costs, Tax Expense (Benefit)	112	103	336	309
Less: accretion of prior service cost included in net periodic pension costs, Tax Expense (Benefit)	(22)	(22)	(66)	(67)
Total defined benefit pension plans, Tax Expense (Benefit)	90	81	270	242
Other comprehensive (loss) income, Tax Expense (Benefit)	(254)	949	(3,651)	1,059
Total comprehensive income, Tax Expense (Benefit)	1,146	2,791	996	5,252
Income, Net of Tax Amount	6,039	5,770	16,267	15,796
Net unrealized (losses) gains on available-for-sale investment securities, Net of Tax Amount
Net unrealized holding (losses) gains arising during the period, Net of Tax Amount	287	1,754	(6,606)	2,090
Less: reclassification adjustment for net gains on sales realized in net income, Net of Tax Amount	(927)	(6)	(1,918)	(189)
Less: reclassification adjustment for other-than-temporary impairment on equity securities realized in net income, Net of Tax Amount		2		8
Total net unrealized (losses) gains on available-for-sale investment securities, Net of Tax Amount	(640)	1,750	(8,524)	1,909
Cash flow hedge derivative, Net of Tax Amount
Net change in fair value of interest rate swap, Net of Tax Amount		(138)	28	(391)
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Net of Tax Amount			1,213
Total cash flow hedge derivative, Net of Tax Amount		(138)	1,241	(391)
Defined benefit pension plans, Net of Tax Amount
Less: amortization of net loss included in net periodic pension costs, Net of Tax Amount	208	190	625	573
Less: accretion of prior service cost included in net periodic pension costs, Net of Tax Amount	(42)	(42)	(125)	(125)
Total defined benefit pension plans, Net of Tax Amount	166	148	500	448
Other comprehensive (loss) income, Net of Tax Amount	(474)	1,760	(6,783)	1,966
Total comprehensive income, Net of Tax Amount	$ 5,565	$ 7,530	$ 9,484	$ 17,762