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Stock-based Compensation - Additional Information (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based compensation expense $ 9.7 $ 10.9 $ 18.1 $ 21.3
Tax benefit from compensation expense 1.9 $ 3.4 3.4 6.3
Proceeds from stock options exercised     10.5 $ 12.9
Tax benefit realized from exercise of stock options     3.9  
Unrecognized compensation cost 6.8   6.8  
Employee Stock Option [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Proceeds from stock options exercised     $ 11.0  
Period for recognition of compensation not yet recognized     1 year 6 months  
Restricted Stock and Restricted Stock Units [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Period for recognition of compensation not yet recognized     1 year 8 months 12 days  
Tax benefit realized on the vesting of restricted stock     $ 0.2  
Compensation not yet recognized, share-based awards other than options 23.8   $ 23.8  
Performance Shares [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Period for recognition of compensation not yet recognized     2 years 1 month 6 days  
Compensation not yet recognized, share-based awards other than options $ 16.9   $ 16.9