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Stock Compensation Plans - Significant Assumptions and Historical Vesting for TSR Performance Stock Awards (Details) - Performance stock awards - Total Stockholder Return
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Significant assumptions used      
Expected dividend yield (as a percent) 1.10% 0.96% 0.00%
Expected volatility (as a percent) 26.80% 25.90% 31.50%
Risk-free interest rates (as a percent) 0.83% 0.93% 0.68%
Performance (vesting) period 3 years 3 years 3 years