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Stock-based Compensation (Schedule of Restricted Stock Outstanding) (Details) - Restricted Stock [Member] - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Shares      
Balance at December 31, 2016 81,269    
Granted 26,064 39,816 47,065
Vested (29,167)    
Forfeited    
Balance at December 31, 2017 78,166 81,269  
Weighted Average Grant Date Fair Value      
Balance at December 31, 2016 $ 46.39    
Granted 59.46    
Vested 47.58    
Forfeited    
Balance at December 31, 2017 $ 50.30 $ 46.39