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STOCK-BASED COMPENSATION PLANS - Stock options granted (Details)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Fair value of stock option grants    
Weighted average expected term 6 years 9 months 14 days 6 years 3 months
Weighted average volatility 117.00% 122.00%
Weighted average risk-free interest rate 1.59% 2.30%
Dividend yield 0.00% 0.00%