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Stockholders' Equity (Schedule of Fair Value of Employee Stock Purchase Plan) (Details) - ESPP [Member] - $ / shares
3 Months Ended
Mar. 31, 2022
Mar. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected volatility 70.00% 68.00%
Risk-free interest rate, minimum 0.60% 0.07%
Risk-free interest rate, maximum 1.31%  
Weighted average grant date fair value, per share $ 5.42 $ 29.26
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
Risk-free interest rate, maximum   0.13%