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Stockholders' Equity (Details 1)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Fair value of stock options granted using the following weighted average assumptions      
Expected volatility 74.00% 65.00% 68.00%
Expected risk-free interest rate 0.90% 2.20% 2.60%
Expected life (years) 4 years 7 months 6 days 4 years 4 months 24 days 4 years 6 months