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Stock-Based Compensation - Narrative (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Employee Stock Option
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Award expiration period 10 years  
Grants in period, weighted average grant date fair value $ 8.86  
Share-based compensation expense $ 0.5 $ 0.9
Tax benefit from compensation expense 0.2 0.4
Compensation cost not yet recognized 7.0  
Compensation cost not yet recognized, period for recognition 2 years  
Employee Stock Option | Minimum
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Award vesting period 4 years  
Employee Stock Option | Maximum
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Award vesting period 5 years  
Restricted Stock Units
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share-based compensation expense 4.6 4.7
Tax benefit from compensation expense 1.7 1.8
Compensation cost not yet recognized $ 58.5  
Compensation cost not yet recognized, period for recognition 2 years  
Restricted Stock Units | Minimum
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Award vesting period 4 years  
Restricted Stock Units | Maximum
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Award vesting period 5 years  
Employee Stock | Common Class A
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares authorized 1.0  
Maximum employee subscription rate 15.00%  
Award offering period 6 months  
Discount from market price 15.00%  
Number of shares available for grant 0.3  
2003 Incentive Compensation Plan
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares authorized 13.5  
Number of shares available for grant 2.0  
WMS Equity Compensation Plan
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares authorized 5.6  
Number of shares available for grant 4.5