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Stockholders' Equity (Schedule of Fair Value of Employee Stock Options) (Details) - Stock Options [Member]
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term in years 4 years 7 months 6 days 5 years 1 month 6 days
Expected volatility 68.00% 57.00%
Risk-free interest rate 0.50% 1.20%
Dividend yield