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Employee Benefit Plans (Schedule of Stock Option Valuation Assumptions) (Details)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Weighted average fair value of options      
Risk free interest rate 1.80% 1.20% 1.40%
Volatility 20.10% 20.40% 21.70%
Dividend yield 1.40% 1.60% 1.60%
Weighted average expected life (years) 4 years 2 months 12 days 4 years 2 months 18 days 4 years 2 months 12 days