SEGMENT INFORMATION - Revenue and Long-Lived Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Revenue and Long-lived Assets by Geography
Revenue	$ 255,311	$ 150,745
Long-lived assets (excluding goodwill and intangible assets)	46,971		$ 53,292
United States
Revenue and Long-lived Assets by Geography
Revenue	233,475	137,466
Long-lived assets (excluding goodwill and intangible assets)	42,420		49,356
All other countries
Revenue and Long-lived Assets by Geography
Revenue	21,836	$ 13,279
Long-lived assets (excluding goodwill and intangible assets)	$ 4,551		$ 3,936