CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - 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
Stockholders' equity, beginning balance at Dec. 31, 2014	$ 346,279	$ 1,047	$ 101,204	$ 252,837	$ (8,809)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	43,465			43,465
Total other comprehensive income (loss), net of tax	(890)				(890)
Cash dividends declared	(23,228)			(23,228)
Share-based compensation	2,074		2,074
Common stock issued for acquisition, shares		137,000
Common stock issued for acquisition	5,430	$ 8	5,422
Exercise of stock options and issuance of other compensation related equity instruments and related tax benefit, shares		137,000
Exercise of stock options and issuance of other compensation related equity instruments and related tax benefit	2,258	$ 9	2,249
Common stock, shares outstanding, ending balance at Dec. 31, 2015		17,020,000
Stockholders' equity, ending balance at Dec. 31, 2015	375,388	$ 1,064	110,949	273,074	(9,699)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	46,481			46,481
Total other comprehensive income (loss), net of tax	(10,058)				(10,058)
Cash dividends declared	(25,190)			(25,190)
Share-based compensation	2,190		2,190
Common stock issued for acquisition	0
Exercise of stock options and issuance of other compensation related equity instruments and related tax benefit, shares		151,000
Exercise of stock options and issuance of other compensation related equity instruments and related tax benefit	$ 1,993	$ 9	1,984
Common stock, shares outstanding, ending balance at Dec. 31, 2016	17,170,820	17,171,000
Stockholders' equity, ending balance at Dec. 31, 2016	$ 390,804	$ 1,073	115,123	294,365	(19,757)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	45,925			45,925
Total other comprehensive income (loss), net of tax	472				472
Cash dividends declared	(26,759)			(26,759)
Share-based compensation	2,577		2,577
Common stock issued for acquisition	0
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit, shares		56,000
Exercise of stock options, issuance of other compensation-related equity instruments and related tax benefit	265	$ 4	261
Reclassification of income tax effects due to the adoption of ASU 2018-02	$ 0			4,225	(4,225)
Common stock, shares outstanding, ending balance at Dec. 31, 2017	17,226,508	17,227,000
Stockholders' equity, ending balance at Dec. 31, 2017	$ 413,284	$ 1,077	$ 117,961	$ 317,756	$ (23,510)