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Share-Based Compensation - Valuation Assumptions (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Equity [Abstract]      
Risk-free interest rate 2.67% 1.84% 1.51%
Expected life in years 6 years 5 years 5 years
Expected volatility 20.00% 21.00% 24.00%
Expected dividend yield 1.43% 1.40% 1.36%
Estimated fair value of options granted per share (in dollars per share) $ 14.08 $ 10.50 $ 9.88