NET LOSS PER SHARE - Schedule of basic and diluted net loss per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net loss attributable to common stock	$ (19,283)	$ (10,693)	$ (27,513)	$ (20,336)
Weighted average shares outstanding, basic and diluted (in shares)	79,507	52,062	71,971	52,241
Net loss per share, basic and diluted (in dollars per share)	$ (0.24)	$ (0.21)	$ (0.38)	$ (0.39)
Anti-dilutive securities excluded from diluted net loss per share calculation for stock-based compensation plans (in shares)	6,255	6,084	6,255	6,084