NET LOSS PER SHARE - SUMMARY OF BASIC AND DILUTED NET LOSS PER COMMON 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
Earnings Per Share [Abstract]
Net loss	$ (4,375)	$ (6,550)	$ (8,284)	$ (13,144)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.10)	$ (0.16)	$ (0.20)	$ (0.33)
Weighted-average shares used to compute net loss per share attributable to common stockholders, basic and diluted (in shares)	43,146,930	39,706,473	41,958,305	39,578,246