NET LOSS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Basic and diluted net loss per share
Net loss	$ (15,992)	$ (12,894)	$ (69,392)	$ (44,352)
Denominator (in shares)	62,997,484	61,422,015	62,555,921	61,163,059
Basic and diluted net loss per share (in dollars per share)	$ (0.25)	$ (0.21)	$ (1.11)	$ (0.73)
Potentially dilutive common shares:
Total potentially dilutive common shares (in shares)			25,324,000	27,413,000
Convertible Notes
Potentially dilutive common shares:
Total potentially dilutive common shares (in shares)			17,931,000	17,931,000
Stock options and equivalents
Potentially dilutive common shares:
Total potentially dilutive common shares (in shares)			7,393,000	9,482,000