Consolidated Statements of Changes in Shareholders' Equity (USD $) In Thousands, except Share data	Total USD ($)	Common Shares Outstanding	Accumulated Other Comprehensive (Loss) Income USD ($)	Common Stock USD ($)	Additional Paid-in Capital USD ($)	Retained Earnings USD ($)	Treasury Stock USD ($)
Beginning balance at Dec. 31, 2009	$ 267,807		$ (524)	$ 91,332	$ 60,126	$ 150,507	$ (33,634)
Beginning balance, shares at Dec. 31, 2009		16,465,083
Net income	15,756					15,756
Other comprehensive income, net of income tax	(6,242)		(6,242)
Cash dividends declared ($0.80 per share)	(13,284)					(13,284)
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs	2,189					(605)	2,794
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs, shares		123,750
Purchases of treasury stock	(153)						(153)
Purchases of treasury stock, shares		(8,512)
Restricted stock awards granted	(9)				(1,206)	(396)	1,593
Restricted stock awards granted, shares		67,982
Vesting of restricted stock awards	160				160
Ending balance at Dec. 31, 2010	266,224		(6,766)	91,332	59,080	151,978	(29,400)
Ending balance, shares at Dec. 31, 2010		16,648,303
Net income	18,882					18,882
Other comprehensive income, net of income tax	665		665
Cash dividends declared ($0.80 per share)	(13,382)					(13,382)
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs	2,287				65	13	2,209
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs, shares		141,485
Expired stock options	28					28
Purchases of treasury stock	(1,928)						(1,928)
Purchases of treasury stock, shares		(137,494)
Restricted stock awards granted					(1,019)	47	972
Restricted stock awards granted, shares		58,736
Vesting of restricted stock awards	203				203
Repurchase of cancelled restricted stock awards					166		(166)
Repurchase of cancelled restricted stock awards, shares		(8,654)
Ending balance at Dec. 31, 2011	272,979		(6,101)	91,332	58,495	157,556	(28,313)
Ending balance, shares at Dec. 31, 2011		16,702,376
Net income	20,872					20,872
Other comprehensive income, net of income tax	(819)		(819)
Cash dividends declared ($0.80 per share)	(13,411)					(13,411)
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs	2,515					(70)	2,585
Stock issued under dividend reinvestment and employee stock purchase plans and other employee benefit programs, shares		150,579
Purchases of treasury stock	(2,319)						(2,319)
Purchases of treasury stock, shares		(140,755)
Restricted stock awards granted					(1,154)	(134)	1,288
Restricted stock awards granted, shares		71,157
Stock-based compensation	4,544				4,544
Repurchase of cancelled restricted stock awards					300		(300)
Repurchase of cancelled restricted stock awards, shares		(13,125)
Tax expense on stock based compensation	(84)				(84)
Ending balance at Dec. 31, 2012	$ 284,277		$ (6,920)	$ 91,332	$ 62,101	$ 164,823	$ (27,059)
Ending balance, shares at Dec. 31, 2012		16,770,232