CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (USD $) In Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Stockholders' Equity, Beginning Balance at Dec. 31, 2008	$ 235,111	$ 1,001	$ 82,095	$ 164,679	$ (10,458)	$ (2,206)
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2008		15,935
Cumulative effect adjustment of change in accounting principle, net of tax	0			1,196	(1,196)
Net income	16,096			16,096
Unrealized gains on securities, net of tax	10,334				10,334
Noncredit-related losses on securities not expected to be sold, net of tax	(2,261)				(2,261)
Reclassification adjustments for net realized losses (gains) on securties included net income, net of tax	4,077				4,077
Defined benefit plan obligation adjustment, net of tax	2,878				2,878
Unrealized gains (losses) on cash flow hedges, net of tax	13				13
Reclassification adjustments for net realized (losses) gains included in net income, net of tax	(50)				(50)
Comprehensive income	31,087
Cash dividends declared	(13,457)			(13,457)
Share-based compensation	708		708
Deferred compensation plan, shares		3
Deferred compensation plan	53		(40)			93
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		44
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	338	1	(504)			841
Shares issued - dividend reinvestment plan, shares		61
Shares issued - dividend reinvestment plan	1,106	2	333			771
Stockholders' Equity, Ending Balance at Dec. 31, 2009	254,946	1,004	82,592	168,514	3,337	(501)
Common Stock, Shares Outstanding, Ending Balance at Dec. 31, 2009		16,043
Net income	24,051			24,051
Unrealized gains on securities, net of tax	1,099				1,099
Reclassification adjustments for net realized losses (gains) on securties included net income, net of tax	(311)				(311)
Credit-related OTTI realized losses transferred to net income, net of tax	111				111
Defined benefit plan obligation adjustment, net of tax	452				452
Unrealized gains (losses) on cash flow hedges, net of tax	(915)				(915)
Reclassification adjustments for net realized (losses) gains included in net income, net of tax	252				252
Comprehensive income	24,739
Cash dividends declared	(13,626)			(13,626)
Share-based compensation	909		909
Deferred compensation plan, shares		3
Deferred compensation plan	44		(20)			64
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		69
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	850	5	841			4
Shares issued - dividend reinvestment plan, shares		57
Shares issued - dividend reinvestment plan	1,002	2	567			433
Stockholders' Equity, Ending Balance at Dec. 31, 2010	268,864	1,011	84,889	178,939	4,025	0
Common Stock, Shares Outstanding, Ending Balance at Dec. 31, 2010		16,172
Net income	29,724			29,724
Unrealized gains on securities, net of tax	1,622				1,622
Reclassification adjustments for net realized losses (gains) on securties included net income, net of tax	(415)				(415)
Credit-related OTTI realized losses transferred to net income, net of tax	88				88
Defined benefit plan obligation adjustment, net of tax	(6,759)				(6,759)
Unrealized gains (losses) on cash flow hedges, net of tax	(942)				(942)
Reclassification adjustments for net realized (losses) gains included in net income, net of tax	486				486
Comprehensive income	23,804
Cash dividends declared	(14,465)			(14,465)
Share-based compensation	1,394		1,394
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		87
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	1,000	5	995
Shares issued - dividend reinvestment plan, shares		33
Shares issued - dividend reinvestment plan	754	2	752
Stockholders' Equity, Ending Balance at Dec. 31, 2011	$ 281,351	$ 1,018	$ 88,030	$ 194,198	$ (1,895)	$ 0
Common Stock, Shares Outstanding, Ending Balance at Dec. 31, 2011		16,292