SELECTED QUARTERLY INFORMATION (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended									12 Months Ended
		Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
NET REVENUES		$ 108,249		$ 111,255	$ 107,563	$ 104,688	$ 102,436	$ 101,625	$ 97,571	$ 88,036	$ 431,755	$ 389,668	$ 344,609
Gross Profit		54,028		55,713	53,447	50,476	50,076	49,842	47,785	44,488	213,664	192,191	173,300
Net income (loss)		$ (16,898)	[1]	$ 16,506	$ 13,902	$ 14,099	$ 14,303	$ 12,809	$ 11,407	$ 10,379	$ 27,609	$ 48,898	$ 39,152
Earnings per share
Basic		$ (0.57)		$ 0.55	$ 0.47	$ 0.48	$ 0.49	$ 0.44	$ 0.40	$ 0.36	$ 0.93	$ 1.69	$ 1.35
Diluted	[2]	$ (0.57)		$ 0.54	$ 0.46	$ 0.47	$ 0.48	$ 0.43	$ 0.39	$ 0.35	$ 0.90	$ 1.65	$ 1.32
Shares used in per share calculation
Basic		29,759		29,759	29,720	29,456	29,196	28,972	28,850	28,679	29,674	28,925	29,001
Diluted	[2]	29,759		30,614	30,454	30,248	29,914	29,625	29,422	29,244	30,545	29,619	29,696

[1] In December 2017 the U.S. government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (Refer to Note 11, Provision for Income Taxes, in the Notes to Consolidated Financial Statements).

[2] The Company includes the shares underlying performance-based awards in the calculation of diluted earnings per share if the performance conditions have been satisfied as of the end of the reporting period and excludes such shares when the necessary conditions have not been met. The Company has included in the 2017, 2016 and 2015 calculations those shares that were contingently issuable upon the satisfaction of the performance conditions as of the end of the respective periods.