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Stock Based Compensation (Weighted Average Assumptions Used to Value Option Grants) (Details) - Employee Stock Option
9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate (%) 2.63% 2.03%
Expected option life (years) 5 years 3 months 25 days 5 years 3 months 4 days
Expected volatility (%) 18.04% 18.76%
Expected dividend yield (%) 0.59% 0.67%