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Stockholders' Equity And Stock-Based Compensation (Schedule Of Fair Value Of Employee Stock Options) (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Options outstanding [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected volatility 70.00%    
Options outstanding [Member] | Minimum [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term in years 4 months 24 days 5 years 3 months 18 days 4 months 24 days
Expected volatility   70.00% 70.00%
Risk-free interest rate 1.40% 2.60% 1.00%
Options outstanding [Member] | Maximum [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term in years 6 years 1 month 6 days 6 years 1 month 6 days  
Expected volatility     90.00%
Risk-free interest rate 2.60% 3.00% 2.20%
2017 Employee Stock Purchase Plan [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected volatility 70.00% 70.00% 95.00%
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 6 months
Risk-free interest rate 1.70% 1.90% 1.10%
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 1 year 3 months 18 days
Risk-free interest rate 2.60% 2.50% 1.20%