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INVESTMENTS - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Gain (loss) from changes in fair value of investments	$ (244)	$ (3,955)	$ (8,312)	$ (5,100)
Impairment of other equity investment			4,600
Monster LP
Schedule of Equity Method Investments [Line Items]
Fair value of investments	70,200		70,200		$ 78,900
Gain (loss) from changes in fair value of investments	(474)	(3,768)	(8,759)	(1,492)
Nearbuy
Schedule of Equity Method Investments [Line Items]
Fair value of investments	4,500		4,500		$ 4,000
Gain (loss) from changes in fair value of investments	$ 230	$ (187)	$ 447	$ (3,608)