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Stockholders' Equity - Black Scholes option (Details)
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Expected term (years)   5 years 10 months 6 days   5 years 10 months 6 days
Expected volatility 93.00% 99.00%    
Expected dividends 0.00% 0.00% 0.00% 0.00%
Minimum        
Expected term (years) 5 years 10 months 6 days   5 years 10 months 6 days  
Risk free interest rate 0.80% 0.34% 0.45% 0.34%
Expected volatility     93.00% 96.00%
Maximum        
Expected term (years) 10 years   10 years  
Risk free interest rate 1.58% 0.38% 1.58% 1.32%
Expected volatility     94.00% 99.00%