SEGMENT INFORMATION - SCHEDULE OF REVENUE AND LONG-LIVED ASSETS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue and Long-lived Assets by Geography
Revenue	$ 223,213	$ 181,717	$ 180,711	$ 150,745	$ 123,668	$ 133,560	$ 130,173	$ 111,489	$ 736,386	$ 498,890	$ 361,201
Property and equipment, net	53,292				23,645				53,292	23,645
United States
Revenue and Long-lived Assets by Geography
Revenue									672,159	461,372	329,117
Property and equipment, net	49,356				21,775				49,356	21,775
All other countries
Revenue and Long-lived Assets by Geography
Revenue									64,227	37,518	$ 32,084
Property and equipment, net	$ 3,936				$ 1,870				$ 3,936	$ 1,870