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	21,947			21,947
Total other comprehensive income (loss), net of tax	2,943				2,943
Cash dividends declared	(10,844)			(10,844)
Share-based compensation	1,037		1,037
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		74
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	793	4	789
Shares issued - dividend reinvestment plan, shares		33
Shares issued - dividend reinvestment plan	754	2	752
Stockholders' Equity, Ending Balance at Sep. 30, 2011	285,494	1,017	87,467	190,042	6,968
Common Stock, Shares Outstanding, Ending Balance at Sep. 30, 2011		16,279
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	26,051			26,051
Total other comprehensive income (loss), net of tax	(202)				(202)
Cash dividends declared	(11,610)			(11,610)
Share-based compensation	1,404		1,404
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		69
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	1,254	4	1,250
Stockholders' Equity, Ending Balance at Sep. 30, 2012	$ 298,394	$ 1,023	$ 90,829	$ 208,639	$ (2,097)
Common Stock, Shares Outstanding, Ending Balance at Sep. 30, 2012		16,371