SEGMENT AND GEOGRAPHICAL CONCENTRATION - Revenues by Geographic Area (Details) - USD ($) $ 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
Segment Reporting Information [Line Items]
Revenue	$ 67,801	$ 62,653	$ 65,692	$ 61,885	$ 61,791	$ 59,310	$ 59,227	$ 56,306	$ 258,031	$ 236,634	$ 216,007
United States [Member]
Segment Reporting Information [Line Items]
Revenue									197,312	181,078	155,291
International [Member]
Segment Reporting Information [Line Items]
Revenue									60,719	55,556	60,716
Sales Revenue, Net [Member]
Segment Reporting Information [Line Items]
Revenue									258,031	236,634	216,007
Sales Revenue, Net [Member] | United States [Member]
Segment Reporting Information [Line Items]
Revenue									197,312	181,078	155,291
Sales Revenue, Net [Member] | International [Member]
Segment Reporting Information [Line Items]
Revenue									$ 60,719	$ 55,556	$ 60,716