CONCENTRATION OF RISK - Long-Lived Assets (Net) by Geographic Area (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total long-lived assets	$ 58,428	$ 56,450
UNITED STATES
Segment Reporting Information [Line Items]
Total long-lived assets	55,777	53,991
Other [Member]
Segment Reporting Information [Line Items]
Total long-lived assets	$ 2,651	$ 2,459