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]
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		16,292,000
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
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
Stockholders' Equity, Ending Balance at Dec. 31, 2012	295,652	1,024	91,453	213,674	(10,499)
Common Stock, Shares Outstanding, Ending Balance at Dec. 31, 2012		16,380,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	36,153			36,153
Total other comprehensive income (loss), net of tax	8,946				8,946
Cash dividends declared	17,232			17,232
Share-based compensation	1,876		1,876
Deferred compensation plan, shares		2,000
Deferred compensation plan	30		30
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		232,000
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	4,221	14	4,207
Stockholders' Equity, Ending Balance at Dec. 31, 2013	329,646	1,038	97,566	232,595	(1,553)
Common Stock, Shares Outstanding, Ending Balance at Dec. 31, 2013	16,613,561	16,614,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,824			40,824
Total other comprehensive income (loss), net of tax	(7,256)				(7,256)
Cash dividends declared	20,582			20,582
Share-based compensation	1,880		1,880
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		132,000
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	1,767	9	1,758
Stockholders' Equity, Ending Balance at Dec. 31, 2014	$ 346,279	$ 1,047	$ 101,204	$ 252,837	$ (8,809)
Common Stock, Shares Outstanding, Ending Balance at Dec. 31, 2014	16,746,363	16,746,000