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Share-Based Arrangements (Employee Stock Purchase Plan) (Details) - ESPP Stock - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award      
Market price after discount, purchase date 85.00%    
Number of shares authorized 1,500,000    
Employee stock issued (in shares) 74,273 79,294 76,805
Number of shares available for purchase 235,065    
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award      
Employee stock issued (in dollars per share) $ 32.95 $ 31.64 $ 32.48
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award      
Employee stock issued (in dollars per share) $ 42.40 $ 36.46 $ 36.42