PROPERTY AND EQUIPMENT - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 109,712	$ 95,455
Less accumulated depreciation and amortization	(84,932)	(83,714)
Property and equipment, net	$ 24,780	11,741
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 67,415	63,622
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Software
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Property and equipment, gross	$ 21,977	19,378
Software | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Software | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,892	698
Furniture and fixtures | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Furniture and fixtures | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Property and equipment, gross	$ 18,428	$ 11,757
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	1 year
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years