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STOCKHOLDERS' EQUITY - Fair value assumptions of options (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Volatility, minimum 172.99% 192.76%
Volatility, maximum 291.61% 296.71%
Risk-free rate, minimum 1.82% 2.49%
Risk-free rate, maximum 2.49% 2.56%
Minimum [Member]    
Expected term (in years) 5 years 5 years
Maximum [Member]    
Expected term (in years) 6 years 3 months 6 years 3 months