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Share-Based Compensation (Restricted Stock Unit Activity) (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Number of units      
Converted into shares of common stock, Number of Units (179,887) (621,355) (229,055)
Restricted Stock Units      
Number of units      
Beginning balance, Number of Units 380,940    
Granted, Number of Units 321,043    
Converted into shares of common stock, Number of Units (102,553)    
Forfeited/expired, Number of Units (22,940)    
Ending balance, Number of Units 576,490 380,940  
Weighted-average grant date fair value per unit      
Beginning balance, Weighted Average Grant Date Fair Value Per Share (USD per share) $ 41.29    
Granted, Weighted Average Grant Date Fair Value Per Unit (USD per Unit) 54.15    
Converted into shares of common stock, Weighted Average Grant Date Fair Value Per Unit (USD per Unit) 34.77    
Forfeited/expired, Weighted Average Grant Date Fair Value Per Unit (USD per Unit) 47.87    
Ending balance, Weighted Average Grant Date Fair Value Per Share (USD per share) $ 49.35 $ 41.29