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Stock Incentive Plan Stock Incentive Plan (Restricted Stock Units) (Details) - Restricted Stock Units (RSUs) - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Weighted average grant date fair value (in dollars per share) $ 45.10 $ 44.03
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]    
Shares awarded but not earned at January 1 (in shares) 137,396  
Shares awarded (in shares) 141,202  
Shares forfeited (in shares) (9,418)  
Shares earned (in shares) (46,450)  
Shares awarded but not earned at December 31 (in shares) 222,730 137,396