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Stockholders' Equity And Stock-Based Compensation (Schedule Of Fair Value Of Employee Stock Options) (Details)
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Employee Stock Option [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected volatility 70.00% 70.00%
Employee Stock Option [Member] | Minimum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term in years 6 years 1 month 6 days 4 months 24 days
Risk-free interest rate 0.40% 2.40%
Employee Stock Option [Member] | Maximum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term in years   6 years 1 month 6 days
Risk-free interest rate 1.70% 2.70%
2017 Employee Stock Purchase Plan [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected volatility 70.00% 70.00%
2017 Employee Stock Purchase Plan [Member] | Minimum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term in years 6 months 6 months
Risk-free interest rate 0.90% 2.50%
2017 Employee Stock Purchase Plan [Member] | Maximum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term in years 1 year 1 year
Risk-free interest rate 1.00% 2.60%