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Pension and Other Postretirement Benefits - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Defined contribution expense $ 10.9 $ 9.0 $ 8.1
Accumulated benefit obligation 258.9 235.4  
Project benefit obligation for the pension plans with an accumulated benefit obligation in excess of plan assets 219.4 200.7  
Accumulated benefit obligation for the pension plans with an accumulated benefit obligation in excess of assets 214.7 196.2  
Fair value of plan assets for the pension plans with an accumulated benefit obligations in excess of plan assets 120.0 112.0  
Projected benefit obligation for the pension plans with an accumulated benefit less than plan assets 44.5 39.3  
Accumulated benefit obligation for the pension plans with an accumulated benefit obligation less than plan assets 44.2 39.2  
Fair value of plan assets for the pension plans with an accumulated benefit obligations less than plan assets 53.2 48.8  
Target asset allocation for the investment of the assets in equity securities minimum 20.00%    
Target asset allocation for the investment of the assets in equity securities maximum 25.00%    
Target asset allocation for the investment of the assets in fixed income securities minimum 75.00%    
Target asset allocation for the investment of the assets in fixed income securities maximum 80.00%    
Pension Benefits [Member]
     
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Pension and other postretirement plans 10.5    
Other benefit [Member]
     
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Pension and other postretirement plans $ 2.8    
Minimum [Member]
     
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Target asset allocation for the investment of the assets in fixed income securities 30.00%    
Target asset allocation for the investment of the assets in equity securities 60.00%    
Maximum [Member]
     
Pension Plans, Postretirement and Other Employee Benefits [Line Items]      
Target asset allocation for the investment of the assets in fixed income securities 40.00%    
Target asset allocation for the investment of the assets in equity securities 70.00%