SEGMENT INFORMATION - Revenue and Long-Lived Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenue and Long-lived Assets by Geography
Revenue	$ 294,822	$ 180,711	$ 550,133	$ 331,456
Long-lived assets (excluding goodwill and intangible assets)	53,396		53,396		$ 53,292
United States
Revenue and Long-lived Assets by Geography
Revenue	274,785	163,669	508,260	301,135
Long-lived assets (excluding goodwill and intangible assets)	48,684		48,684		49,356
All other countries
Revenue and Long-lived Assets by Geography
Revenue	20,037	$ 17,042	41,873	$ 30,321
Long-lived assets (excluding goodwill and intangible assets)	$ 4,712		$ 4,712		$ 3,936