NET LOSS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Basic and diluted net loss per share
Net loss	$ (12,894)	$ (11,785)	$ (44,352)	$ (45,070)
Denominator (in shares)	61,422,015	60,320,369	61,163,059	59,960,507
Basic and diluted net loss per share (in dollars per share)	$ (0.21)	$ (0.20)	$ (0.73)	$ (0.75)
Diluted net loss per share
Total potentially dilutive common shares (in shares)			27,413,000	26,297,000
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)			9,482,000	8,366,000