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Stock Compensation (Schedule Of Weighted-Average Assumptions Used To Determine The Fair Value Of Options) (Details)
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Stock Options [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life of options 5 years 5 years
Expected stock price volatility 0.40% 0.40%
Risk-free interest rate 2.54% 2.64%
ESPP Options [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life of options 6 months 6 months
Expected stock price volatility 0.39% 0.35%
Risk-free interest rate 2.56% 1.53%