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, 2016		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		17,210,000
Shareholders' Equity, Ending Balance at Jun. 30, 2017	$ 406,042	$ 1,076	116,484	306,151	(17,669)
Common Stock, Shares Outstanding, Beginning Balance at Dec. 31, 2017	17,226,508	17,227,000
Shareholders' Equity, Beginning Balance at Dec. 31, 2017	$ 413,284	$ 1,077	117,961	317,756	(23,510)
Net income	33,885			33,885
Total other comprehensive income (loss), net of tax	(11,552)				(11,552)
Cash dividends declared	(14,971)			(14,971)
Share-based compensation	1,319		1,319
Exercise of stock options and issuance of other compensation-related equity awards, shares		51,000
Exercise of stock options and issuance of other compensation-related equity awards, value	$ (394)	$ 3	(397)
Common Stock, Shares Outstanding, Ending Balance at Jun. 30, 2018	17,278,116	17,278,000
Shareholders' Equity, Ending Balance at Jun. 30, 2018	$ 421,571	$ 1,080	$ 118,883	$ 336,670	$ (35,062)