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	22,513			22,513
Total other comprehensive income (loss), net of tax	(274)				(274)
Cash dividends declared	(11,560)			(11,560)
Share-based compensation	1,156		1,156
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		88,000
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	1,053	$ 5	1,048
Common Stock, Shares Outstanding, Ending Balance at Jun. 30, 2015		16,834,000
Shareholders' Equity, Ending Balance at Jun. 30, 2015	$ 359,167	$ 1,052	103,408	263,790	(9,083)
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	21,992			21,992
Total other comprehensive income (loss), net of tax	1,983				1,983
Cash dividends declared	(12,400)			(12,400)
Share-based compensation	1,109		1,109
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		61,000
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	$ 260	$ 4	256
Common Stock, Shares Outstanding, Ending Balance at Jun. 30, 2016	17,081,124	17,081,000
Shareholders' Equity, Ending Balance at Jun. 30, 2016	$ 388,332	$ 1,068	$ 112,314	$ 282,666	$ (7,716)