SUBSEQUENT EVENTS (Details) - USD ($)		1 Months Ended		12 Months Ended
	Feb. 17, 2021	Feb. 28, 2021	Nov. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Common stock, par value (in dollars per share)				$ 0.001	$ 0.001
Stock options granted (in shares)				4,044,000	3,986,000	3,546,000
Granted exercise price (in dollars per share)				$ 0.87	$ 1.02	$ 1.71
Stock options | 2014 Stock Incentive Plan
Subsequent Event [Line Items]
Award vesting period				4 years
Award expiration period				10 years
ATM Facility
Subsequent Event [Line Items]
Aggregate sales price			$ 35,000,000.0
Subsequent Event | Stock options | Share-based Payment Arrangement, Nonemployee | 2014 Stock Incentive Plan
Subsequent Event [Line Items]
Stock options granted (in shares)		4,100,000
Granted exercise price (in dollars per share)		$ 3.17
Stock options grant-date fair value (in dollars per share)		$ 2.06
Vesting rights rate		6.25%
Award vesting period		3 months
Award expiration period		4 years
Subsequent Event | ATM Facility
Subsequent Event [Line Items]
Common stock, par value (in dollars per share)	$ 0.001
Additional shares to be issued	$ 34,500,000
Aggregate sales price	$ 35,500,000