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Stockholders' Equity (Schedule of Fair Value of Employee Stock Purchase Plan) (Details) - ESPP [Member]
3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expected volatility 71.00%  
Risk-free interest rate    
Risk-free interest rate, minimum 0.10%   0.10%  
Risk-free interest rate, maximum     1.00%  
Dividend yield
Minimum [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expected term in years 6 months   6 months  
Expected volatility       57.00%
Maximum [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expected term in years 2 years   2 years  
Expected volatility       71.00%