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Stockholders' Equity (Schedule Of Fair Value Of Employee Stock Options) (Details)
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Risk-free interest rate, maximum     1.30%  
Stock Options [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expected term 6 years 1 month 6 days 6 years 1 month 6 days 6 years 1 month 6 days 6 years 1 month 6 days
Expected volatility 70.00% 70.00% 70.00% 70.00%
Risk-free interest rate 1.90% 1.40% 2.10% 1.50%
Dividend yield