NET LOSS PER SHARE - Computation of Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net loss attributable to common stockholders	$ (17,912)	$ (14,571)	$ (12,145)	$ (9,268)	$ (12,287)	$ (3,828)	$ (44,628)	$ (25,383)
Weighted average common shares outstanding, basic and diluted	35,927,485			2,065,676			31,860,716	2,054,115
Net loss per share, basic and diluted (in dollars per share)	$ (0.50)			$ (4.50)			$ (1.42)	$ (12.36)