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Share-Based Payments (Weighted Average Assumptions for Employee Stock Purchase Plan and Other Options) (Details) - Employee Stock Purchase Plan [Member]
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Risk-free interest rate 1.88% 1.07% 0.47%
Expected term 6 months 6 months 6 months
Dividend yield 1.30% 1.30% 1.70%
Expected volatility 18.00% 24.00% 31.00%