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]
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2014		16,746,000
Shareholders' Equity, Beginning Balance at Dec. 31, 2014	$ 346,279	$ 1,047	$ 101,204	$ 252,837	$ (8,809)
Net income	32,721			32,721
Total other comprehensive income (loss), net of tax	384				384
Cash dividends declared	(17,392)			(17,392)
Share-based compensation	1,640		1,640
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		102,000
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	1,465	$ 7	1,458
Common Stock, Shares Outstanding, Ending Balance at Sep. 30, 2015		16,985,000
Shareholders' Equity, Ending Balance at Sep. 30, 2015	$ 370,527	$ 1,062	109,724	268,166	(8,425)
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2015	17,019,578	17,020,000
Shareholders' Equity, Beginning Balance at Dec. 31, 2015	$ 375,388	$ 1,064	110,949	273,074	(9,699)
Net income	34,319			34,319
Total other comprehensive income (loss), net of tax	2,054				2,054
Cash dividends declared	(18,780)			(18,780)
Share-based compensation	1,634		1,634
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	$ 712	$ 5	707
Common Stock, Shares Outstanding, Ending Balance at Sep. 30, 2016	17,107,476	17,107,000
Shareholders' Equity, Ending Balance at Sep. 30, 2016	$ 395,327	$ 1,069	$ 113,290	$ 288,613	$ (7,645)