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Stock-Based Compensation (Assumptions Used To Value Option Grants, Stock Awards and ESPP Shares) (Details) - 2015 ESPP Plan [Member]
3 Months Ended 9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]        
Expected life (in years) 6 months 6 months 6 months 6 months
Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]        
Expected volatility factor 21.00% 22.00% 21.00% 22.00%
Risk free interest rate 0.13% 2.06% 0.13% 2.06%
Expected dividend yield 0.92% 1.31% 0.92% 1.27%
Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]        
Expected volatility factor 35.00% 29.00% 35.00% 29.00%
Risk free interest rate 1.56% 2.49% 2.06% 2.49%
Expected dividend yield 1.20% 1.39% 1.39% 1.39%