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Share-Based Payments and Other Compensation - Weighted Average Assumptions (Details) - Stock Options - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation      
Volatility rate 33.70% 40.50% 38.00%
Risk-free interest rate 1.46% 0.91% 1.10%
Expected life (years) 2 years 11 months 1 day 2 years 10 months 28 days 2 years 11 months 12 days
Weighted average fair value of units granted (in dollars per share) $ 19.19 $ 3.37 $ 5.95