NET LOSS PER SHARE - Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Numerator:
Net loss	$ (105,891)	$ (38,151)
Denominator:
Weighted-average shares used to compute basic and diluted net loss per share (in shares)	434,940	419,289
Net loss per share:
Basic (in USD per share)	$ (0.24)	$ (0.09)
Diluted (in USD per share)	$ (0.24)	$ (0.09)