SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - SCHEDULE OF ESTIMATED USEFUL LIVES OF PROPERTY AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property and equipment, net of accumulated depreciation and amortization :
Property and equipment, net	$ 53,292	$ 23,645
Computer equipment and capitalized software | Minimum
Property and equipment, net of accumulated depreciation and amortization :
Estimated useful life	2 years
Computer equipment and capitalized software | Maximum
Property and equipment, net of accumulated depreciation and amortization :
Estimated useful life	3 years
Furniture and other equipment | Minimum
Property and equipment, net of accumulated depreciation and amortization :
Estimated useful life	5 years
Furniture and other equipment | Maximum
Property and equipment, net of accumulated depreciation and amortization :
Estimated useful life	7 years
Buildings and leasehold improvements | Minimum
Property and equipment, net of accumulated depreciation and amortization :
Estimated useful life	5 years
Buildings and leasehold improvements | Maximum
Property and equipment, net of accumulated depreciation and amortization :
Estimated useful life	25 years
Capitalized internal use software
Property and equipment, net of accumulated depreciation and amortization :
Property and equipment, net	$ 23,300	$ 14,500