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Stockholders' Equity And Stock-Based Compensation (Schedule Of Fair Value Of Employee Stock Options) (Details)
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Stock Options [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected volatility 78.00% 70.00% 70.00%
Stock Options [Member] | Minimum [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term in years 5 years 3 months 18 days 5 years 3 months 18 days 4 months 24 days
Risk-free interest rate 0.90% 0.30% 1.40%
Stock Options [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  
Risk-free interest rate 1.40% 0.50% 2.60%
2017 Employee Stock Purchase Plan [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected volatility 78.00% 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 6 months
Risk-free interest rate 0.06% 0.10% 1.70%
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
Risk-free interest rate 0.10% 1.00% 2.60%