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Share-Based Arrangements (Restricted Stock Activity) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Nonqualified Stock Options and Restricted Stock      
Restricted Stock, Weighted-Average Grant Date Fair Value [Roll Forward]      
Tax benefit from compensation expense $ 2.0 $ 2.2 $ 1.9
Compensation cost not yet recognized $ 7.4    
Compensation cost recognized, period 2 years 11 months    
Employee Stock Options and ESPP Stock      
Restricted Stock, Weighted-Average Grant Date Fair Value [Roll Forward]      
Windfall tax benefit realized $ 0.0 $ 0.3 0.8
Restricted Stock      
Restricted Stock, Outstanding [Roll Forward]      
Outstanding at beginning of period (in shares) 183,543    
Granted (in shares) 82,519    
Vested (in shares) (87,424)    
Forfeited or expired (in shares) (10,964)    
Outstanding at end of period (in shares) 167,674 183,543  
Restricted Stock, Weighted-Average Grant Date Fair Value [Roll Forward]      
Outstanding at beginning of period (in dollars per share) $ 37.80    
Granted (in dollars per share) 42.73    
Vested (in dollars per share) 37.94    
Forfeited or expired (in dollars per share) 39.71    
Outstanding at end of period (in dollars per share) $ 40.27 $ 37.80  
Total fair value of restricted stock awards vested $ 4.3 $ 3.8 $ 4.5