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, 2015		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 awards and related tax benefit, shares		87,000
Exercise of stock options, issuance of other compensation-related equity awards and related tax benefit, value	712	$ 5	707
Common Stock, Shares Outstanding, Ending Balance at Sep. 30, 2016		17,107,000
Shareholders' Equity, Ending Balance at Sep. 30, 2016	$ 395,327	$ 1,069	113,290	288,613	(7,645)
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2016	17,170,820	17,171,000
Shareholders' Equity, Beginning Balance at Dec. 31, 2016	$ 390,804	$ 1,073	115,123	294,365	(19,757)
Net income	37,943			37,943
Total other comprehensive income (loss), net of tax	3,386				3,386
Cash dividends declared	(19,974)			(19,974)
Share-based compensation	1,872		1,872
Exercise of stock options and issuance of other compensation-related equity awards, shares		43,000
Exercise of stock options and issuance of other compensation-related equity awards, value	$ 197	$ 3	194
Common Stock, Shares Outstanding, Ending Balance at Sep. 30, 2017	17,214,160	17,214,000
Shareholders' Equity, Ending Balance at Sep. 30, 2017	$ 414,228	$ 1,076	$ 117,189	$ 312,334	$ (16,371)