STOCKHOLDERS' EQUITY - Stock grant agreements with non-employees, Stock (Details) - Nonemployees - Researchers, Employees of MSK	1 Months Ended	12 Months Ended						32 Months Ended
	Aug. 31, 2015 individual shares	Dec. 31, 2020 shares	Dec. 31, 2019 individual shares	Dec. 31, 2018 item individual shares	Dec. 31, 2017 shares	Dec. 31, 2016 shares	Dec. 31, 2015 shares	Aug. 31, 2020 item
Share-Based Compensation Awards
Number of individuals | individual	2		1	2
Number of stock grants | item				1
Forecast
Share-Based Compensation Awards
Number of stock grants | item								2
Common Stock
Share-Based Compensation Awards
Shares agreed to be issued	2,800,000
Issuance of common stock to nonemployees (in shares)			400,000	544,000	448,000	448,000	560,000
Common Stock | Forecast
Share-Based Compensation Awards
Issuance of common stock to nonemployees (in shares)		400,000