NET LOSS PER SHARE - Schedule of Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net loss	$ (3,470)	$ (6,854)	$ (12,336)	$ (42,252)
Denominator:
Weighted average common shares outstanding (in shares)	102,798	84,862	97,257	81,993
Net loss per share, basic and diluted (in usd per share)	$ (0.03)	$ (0.08)	$ (0.13)	$ (0.52)