CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Unaudited) (USD $) In Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Stockholders' Equity, Beginning Balance at Dec. 31, 2010	$ 268,864	$ 1,011	$ 84,889	$ 178,939	$ 4,025
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2010		16,172
Net income	14,365			14,365
Total other comprehensive income, net of tax	3,467				3,467
Cash dividends declared	(7,226)			(7,226)
Share-based compensation	680		680
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		73
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	791	4	787
Shares issued - dividend reinvestment plan, shares		21
Shares issued - dividend reinvestment plan	484	2	482
Stockholders' Equity, Ending Balance at Jun. 30, 2011	281,425	1,017	86,838	186,078	7,492
Common Stock, Shares Outstanding, Ending Balance at Jun. 30, 2011		16,266
Stockholders' Equity, Beginning Balance at Dec. 31, 2011	281,351	1,018	88,030	194,198	(1,895)
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2011		16,292
Net income	17,151			17,151
Total other comprehensive income, net of tax	(141)				(141)
Cash dividends declared	(7,623)			(7,623)
Share-based compensation	876		876
Deferred compensation plan, shares		10
Deferred compensation plan	146	1	145
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		57
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	974	3	971
Stockholders' Equity, Ending Balance at Jun. 30, 2012	$ 292,734	$ 1,022	$ 90,022	$ 203,726	$ (2,036)
Common Stock, Shares Outstanding, Ending Balance at Jun. 30, 2012		16,359