Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement Of Income And Comprehensive Income [Abstract]
Income, Before Tax Amount	$ 6,627	$ 6,367	$ 14,358	$ 13,475
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	2,708	(9,201)	5,458	(10,605)
Less: reclassification adjustment for net gains on sales realized in net income, Before Tax Amount	(415)	(1,339)	(557)	(1,524)
Total net unrealized gains (losses) on available-for-sale investment securities, Before Tax Amount	2,293	(10,540)	4,901	(12,129)
Cash flow hedge derivative, Before Tax Amount
Net change in fair value of interest rate swap, Before Tax Amount		(119)		43
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Before Tax Amount		1,866		1,866
Total cash flow hedge derivative, Before Tax Amount		1,747		1,909
Defined benefit pension plans, Before Tax Amount
Less: amortization of net actuarial loss included in net periodic pension costs, Before Tax Amount	167	349	331	641
Less: accretion of prior service cost included in net periodic pension costs, Before Tax Amount	(69)	(63)	(144)	(127)
Total defined benefit pension plans, Before Tax Amount	98	286	187	514
Other comprehensive income (loss), Before Tax Amount	2,391	(8,507)	5,088	(9,706)
Total comprehensive income (loss), Before Tax Amount	9,018	(2,140)	19,446	3,769
Income, Tax Expense (Benefit)	1,547	1,537	3,552	3,247
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)	948	(3,221)	1,911	(3,712)
Less: reclassification adjustment for net gains on sales realized in net income, Tax Expense (Benefit)	(145)	(468)	(195)	(533)
Total net unrealized gains (losses) on available-for-sale investment securities, Tax Expense (Benefit)	803	(3,689)	1,716	(4,245)
Cash flow hedge derivative, Tax Expense (Benefit)
Net change in fair value of interest rate swap, Tax Expense (Benefit)		(42)		15
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Tax Expense (Benefit)		653		653
Total cash flow hedge derivative, Tax Expense (Benefit)		611		668
Defined benefit pension plans, Tax Expense (Benefit)
Less: amortization of net actuarial loss included in net periodic pension costs, Tax Expense (Benefit)	59	122	116	224
Less: accretion of prior service cost included in net periodic pension costs, Tax Expense (Benefit)	(25)	(21)	(51)	(44)
Total defined benefit pension plans, Tax Expense (Benefit)	34	101	65	180
Other comprehensive income (loss), Tax Expense (Benefit)	837	(2,977)	1,781	(3,397)
Total comprehensive income (loss), Tax Expense (Benefit)	2,384	(1,440)	5,333	(150)
Income, Net of Tax Amount	5,080	4,830	10,806	10,228
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	1,760	(5,980)	3,547	(6,893)
Less: reclassification adjustment for net gains on sales realized in net income, Net of Tax Amount	(270)	(871)	(362)	(991)
Total net unrealized gains (losses) on available-for-sale investment securities, Net of Tax Amount	1,490	(6,851)	3,185	(7,884)
Cash flow hedge derivative, Net of Tax Amount
Net change in fair value of interest rate swap, Net of Tax Amount		(77)		28
Less: reclassification adjustment for loss on termination of interest rate swap realized in net income, Net of Tax Amount		1,213		1,213
Total cash flow hedge derivative, Net of Tax Amount		1,136		1,241
Defined benefit pension plans, Net of Tax Amount
Less: amortization of net actuarial loss included in net periodic pension costs, Net of Tax Amount	108	227	215	417
Less: accretion of prior service cost included in net periodic pension costs, Net of Tax Amount	(44)	(42)	(93)	(83)
Total defined benefit pension plans, Net of Tax Amount	64	185	122	334
Other comprehensive income (loss), Net of Tax Amount	1,554	(5,530)	3,307	(6,309)
Total comprehensive income (loss), Net of Tax Amount	$ 6,634	$ (700)	$ 14,113	$ 3,919