INCOME TAXES - Schedule of Income before Income Tax, Domestic and Foreign (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Domestic	$ (202,831)	$ (139,654)	$ (115,137)
Foreign	(7,865)	(12,113)	(10,798)
Loss before income taxes	$ (210,696)	$ (151,767)	$ (125,935)