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Stockholders' Equity (Schedule Of Fair Value Of Employee Stock Options And Employee Stock Purchase Plan) (Details)
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Risk-free interest rate, maximum 1.30% 0.90%
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
Expected volatility 70.00% 70.00%
Risk-free interest rate 2.10% 1.50%
Dividend yield
ESPP [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected volatility 70.00% 70.00%
Risk-free interest rate, minimum 0.80% 0.50%
Dividend yield
ESPP [Member] | Minimum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term 6 months 6 months
ESPP [Member] | Maximum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term 2 years 2 years