NET LOSS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic and diluted net loss per share
Net loss	$ (26,659)	$ (10,541)	$ (53,400)	$ (31,458)
Denominator (in shares)	62,531,696	61,166,044	62,331,471	61,032,155
Basic and diluted net loss per share (in dollars per share)	$ (0.43)	$ (0.17)	$ (0.86)	$ (0.52)
Potentially dilutive common shares:
Total potentially dilutive common shares (in shares)			26,146,000	27,576,000
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)			8,215,000	9,645,000