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Incentive Plans (Assumptions used in Valuation Performance Awards Granted) (Details) - Performance Based Restricted Stock [Member]
12 Months Ended
Dec. 31, 2016
item
$ / shares
Dec. 31, 2015
item
$ / shares
Dec. 31, 2014
item
$ / shares
Assumptions      
Expected volatility 33.00% 26.00% 29.00%
Risk-free interest rate 0.93% 0.85% 0.65%
Stock beta | item 0.863 0.813 0.843
Expected life 3 years 3 years 3 years
Minimum [Member]      
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Fair value per share at grant date $ 12.21 $ 44.03 $ 33.90
Maximum [Member]      
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Fair value per share at grant date $ 16.34 $ 48.12 $ 51.30