INCOME TAXES - Components of Net Income Before Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Loss before provision for income taxes	$ (122,093)	$ (22,526)	$ (26,003)	$ (18,168)	$ (30,227)	$ (37,013)	$ (38,632)	$ (40,576)	$ (188,790)	$ (146,448)	$ (101,867)
United States
Operating Loss Carryforwards [Line Items]
Loss before provision for income taxes									(65,881)	(129,452)	(87,573)
Foreign
Operating Loss Carryforwards [Line Items]
Loss before provision for income taxes									$ (122,909)	$ (16,996)	$ (14,294)