BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Property, Plant and Equipment [Line Items]
Maximum measurement period from the acquisition date within which company records adjustments to the assets acquired and liabilities assumed	1 year
Advertising expense | $	$ 0.3	$ 0.1	$ 0.9
Number of reportable operating segments | segment	1
Leasehold improvements
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
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Minimum | Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	1 year
Minimum | Software
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
Maximum | Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years
Maximum | Software
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years