CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	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, 2009	$ 254,946	$ 1,004	$ 82,592	$ 168,514	$ 3,337	$ (501)
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2009		16,043,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	24,051			24,051
Total other comprehensive income (loss), net of tax	688				688
Cash dividends declared	(13,626)			(13,626)
Share-based compensation	909		909
Deferred compensation plan, shares		3,000
Deferred compensation plan	44		(20)			64
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		69,000
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		57,000
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		16,172,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	29,724			29,724
Total other comprehensive income (loss), net of tax	(5,920)				(5,920)
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		87,000
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	1,000	5	995			0
Shares issued - dividend reinvestment plan, shares		33,000
Shares issued - dividend reinvestment plan	754	2	752			0
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	16,292,471	16,292,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	35,074			35,074
Total other comprehensive income (loss), net of tax	(8,604)				(8,604)
Cash dividends declared	(15,598)			(15,598)
Share-based compensation	1,962		1,962
Deferred compensation plan, shares		10,000
Deferred compensation plan	146	1	145			0
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		78,000
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	1,321	5	1,316			0
Stockholders' Equity, Ending Balance at Dec. 31, 2012	$ 295,652	$ 1,024	$ 91,453	$ 213,674	$ (10,499)	$ 0
Common Stock, Shares Outstanding, Ending Balance at Dec. 31, 2012	16,379,771	16,380,000