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	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 awards and related tax benefit, shares		61,000
Exercise of stock options, issuance of other compensation-related equity awards and related tax benefit, value	260	$ 4	256
Common Stock, Shares Outstanding, Ending Balance at Jun. 30, 2016		17,081,000
Shareholders' Equity, Ending Balance at Jun. 30, 2016	$ 388,332	$ 1,068	112,314	282,666	(7,716)
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	24,981			24,981
Total other comprehensive income (loss), net of tax	2,088				2,088
Cash dividends declared	(13,195)			(13,195)
Share-based compensation	1,198		1,198
Exercise of stock options and issuance of other compensation-related equity awards, shares		39,000
Exercise of stock options and issuance of other compensation-related equity awards, value	$ 166	$ 3	163
Common Stock, Shares Outstanding, Ending Balance at Jun. 30, 2017	17,209,699	17,210,000
Shareholders' Equity, Ending Balance at Jun. 30, 2017	$ 406,042	$ 1,076	$ 116,484	$ 306,151	$ (17,669)