Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in-Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2016	$ 207,475	$ 1,300	$ 92,432	$ 138,789	$ (25,046)
Beginning Balance, shares at Dec. 31, 2016		12,996
Issuance of restricted stock awards		$ 7	(7)
Issuance of restricted stock awards, shares		74
Exercise of stock options	334	$ 29	305
Exercise of stock options, shares		289
Shares withheld related to net share settlement	(2,021)	$ (15)	(2,006)
Shares withheld related to net share settlement, shares		(154)
Share-based compensation	3,660		3,660
Net income	29,963			29,963
Ending Balance at Dec. 31, 2017	239,411	$ 1,321	94,384	168,752	(25,046)
Ending Balance, shares at Dec. 31, 2017		13,205
Issuance of restricted stock awards		$ 10	(10)
Issuance of restricted stock awards, shares		100
Exercise of stock options	$ 9	$ 9
Exercise of stock options, shares	89	88
Shares withheld related to net share settlement	$ (516)	$ (6)	(510)
Shares withheld related to net share settlement, shares		(57)
Share-based compensation	3,950		3,950
Net income	24,575			24,575
Ending Balance at Sep. 30, 2018	$ 267,429	$ 1,334	$ 97,814	$ 193,327	$ (25,046)
Ending Balance, shares at Sep. 30, 2018		13,336