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STOCK-BASED COMPENSATION PLANS - Stock options granted (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Fair value of stock option grants        
Expected term (years) 6 years 4 months 17 days 6 years 3 months 6 years 5 months 1 day 6 years 3 months
Risk-free interest rate 0.34% 1.83% 1.15% 2.34%
Expected volatility 112.97% 121.58% 116.79% 121.83%
Expected dividend yield 0.00% 0.00% 0.00% 0.00%