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Stock Compensation (Schedule Of Weighted-Average Assumptions Used To Determine The Fair Value Of Options) (Details)
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Stock Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected life of options     4 years 9 months 4 years 9 months
Expected stock price volatility     0.40% 0.40%
Risk-free interest rate     1.87% 1.20%
ESPP Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected life of options 6 months 6 months 6 months 6 months
Expected stock price volatility 0.35% 0.30% 0.35% 0.30%
Risk-free interest rate 0.62% 0.49% 0.62% 0.49%