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Stockholders' Equity (Schedule Of Fair Value Of Employee Stock Options And Employee Stock Purchase Plan) (Details)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Risk-free interest rate, maximum 0.90% 0.70% 0.50%
ESPP [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected volatility 70.00% 70.00% 70.00%
Risk-free interest rate, minimum 0.50% 0.10% 0.10%
Dividend yield
ESPP [Member] | Minimum [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected term 6 months 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 2 years
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
Expected volatility 70.00% 70.00% 70.00%
Risk-free interest rate 1.50% 1.70% 1.90%
Dividend yield