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Equity Incentive Program - 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        
Allocated share-based compensation expense $ 7.3 $ 6.2 $ 14.3 $ 12.1
SSARs        
Share-based Compensation Arrangement by Share-based Payment Award        
Unrecognized compensation expense 0.0   0.0  
Stock Options        
Share-based Compensation Arrangement by Share-based Payment Award        
Unrecognized compensation expense 8.6   $ 8.6  
Weighted average period for compensation expense to be recognized     1 year 5 months  
Restricted Stock Units (RSUs)        
Share-based Compensation Arrangement by Share-based Payment Award        
Unrecognized compensation expense 33.0   $ 33.0  
Weighted average period for compensation expense to be recognized     1 year 6 months  
Performance Shares        
Share-based Compensation Arrangement by Share-based Payment Award        
Unrecognized compensation expense $ 8.4   $ 8.4  
Weighted average period for compensation expense to be recognized     2 years 5 months  
Minimum | Performance Shares        
Share-based Compensation Arrangement by Share-based Payment Award        
Percentage increase of initial grant value     0.00%  
Maximum | Performance Shares        
Share-based Compensation Arrangement by Share-based Payment Award        
Percentage increase of initial grant value     225.00%