NET LOSS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Basic and diluted net loss per share
Net loss	$ (10,541)	$ (21,653)	$ (31,458)	$ (33,286)
Denominator (in shares)	61,166,044	59,991,934	61,032,155	59,777,594
Basic and diluted net loss per share (in dollars per share)	$ (0.17)	$ (0.36)	$ (0.52)	$ (0.56)
Diluted net loss per share
Total potentially dilutive common shares (in shares)			27,576,000	26,587,000
Convertible Notes
Diluted net loss per share
Total potentially dilutive common shares (in shares)			17,931,000	17,931,000
Stock options and restricted stock units
Diluted net loss per share
Total potentially dilutive common shares (in shares)			9,645,000	8,656,000