STOCK AWARD PLAN AND STOCK-BASED COMPENSATION - Stock Option Activity for Employees and Non-Employees (Details) - Employees and Non-Employees Stock Option - $ / shares		9 Months Ended	12 Months Ended
		Sep. 30, 2021	Dec. 31, 2020
Shares Issuable Pursuant to Stock Options
Outstanding at the beginning of period (in shares)		10,050,523
Granted (in shares)		140,000
Cancelled/Forfeited (in shares)	[1]	(8,396,056)
Outstanding at the end of the period (in shares)		1,794,467	10,050,523
Exercisable at the end of the period (in shares)		913,530
Available for future grant (in shares)		4,762,269
Weighted-Average Exercise Price
Outstanding at the beginning of period (in dollars per share)		$ 6.60
Granted (in dollars per share)		2.90
Cancelled/forfeited(in dollars per share)	[1]	6.94
Outstanding at the end of the period (in dollars per share)		4.75	$ 6.60
Exercisable at the end of the period (in dollars per share)		$ 5.99
Weighted-Average Remaining Contractual Term Outstanding (Years)		7 years 9 months 18 days	7 years
Weighted-Average Remaining Contractual Term Exercisable (Years)		6 years 7 months 6 days

[1] 7,631,844 shares of the Company’s common stock were cancelled during the Exchange Program