STOCK AWARD PLAN AND STOCK-BASED COMPENSATION - Stock Option Activity for Employees and Non-Employees (Details) - Employees and Non-Employees Stock Option - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Shares Issuable Pursuant to Stock Options
Outstanding at the beginning of period (in shares)	9,040,328
Granted (in shares)	2,148,344
Exercised (in shares)	(198,762)
Forfeited (in shares)	(1,537,500)
Outstanding at the end of the period (in shares)	9,347,054	9,040,328
Exercisable at the end of the period (in shares)	5,543,155
Available for future grant (in shares)	859,510
Expired (in shares)	(105,356)
Weighted-Average Exercise Price
Outstanding at the beginning of period (in dollars per share)	$ 6.98
Granted (in dollars per share)	6.80
Exercised (in dollars per share)	5.75
Forfeited (in dollars per share)	7.20
Outstanding at the end of the period (in dollars per share)	6.90	$ 6.98
Exercisable at the end of the period (in dollars per share)	6.75
Expired (in dollars per share)	$ 9.63
Weighted-Average Remaining Contractual Term Outstanding (Years)	7 years	7 years 3 months 18 days
Weighted-Average Remaining Contractual Term Exercisable (Years)	5 years 10 months 24 days
Total Intrinsic Value Outstanding at the begining of period	$ 7,420
Total Intrinsic Value Outstanding at the end of period		$ 7,420