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Stock Options - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
9 Months Ended 3 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Restricted Stock Units
Sep. 30, 2011
Restricted Stock Units
Sep. 30, 2012
Stock Options
Sep. 30, 2011
Stock Options
Sep. 30, 2012
Minimum
Performance Based Unit
Sep. 30, 2012
Maximum
Performance Based Unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Shares reserved for issuance upon granting 4,000,000              
Number of shares which will vest after achievement of goals             0.0 1.5
Share-based compensation expense recognized $ 11.8 $ 12.8 $ 4.7 $ 5.1 $ 7.1 $ 7.7    
Total intrinsic value of options exercised         0.8 4.4    
Total unrecognized compensation cost     4.8   7.8      
Recognition period for remaining unrecognized compensation expense, weighted-average period (years)     1 year 9 months 18 days   1 year 4 months 24 days      
Aggregate weighted-average grant-date fair value of units granted     3.2 11.3        
Aggregate weighted-average grant-date fair value of units vested     4.1 5.5        
Cash received from stock options exercised $ 0.4 $ 1.4