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Equity - Valuation Assumptions (Details) - $ / shares
9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Equity [Abstract]    
Risk-free interest rate 1.84% 1.51%
Expected life in years 5 years 5 years
Expected volatility 21.00% 24.00%
Expected dividend yield 1.40% 1.36%
Estimated weighted-average fair value of options granted per share (in dollars per share) $ 10.50 $ 9.88