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Stockholders' Equity (Schedule of Fair Value of Employee Stock Purchase Plan) (Details) - ESPP [Member]
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected volatility 68.00% 57.00%
Risk-free interest rate, minimum 0.07% 0.80%
Risk-free interest rate, maximum 0.13% 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
Maximum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term in years 2 years 2 years