GEOGRAPHIC AND OPERATING SEGMENT INFORMATION - Summary by Product and Type of Service (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue from External Customer [Line Items]
Service	$ 148,823	$ 106,210	$ 107,121
Maintenance
Revenue from External Customer [Line Items]
Service	114,735	86,995	89,280
Professional services
Revenue from External Customer [Line Items]
Service	$ 34,088	$ 19,215	$ 17,841