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Share-Based Compensation - Restricted Stock Units - Additional Information (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation (income) expense $ 7.1 $ 7.4 $ 11.1 $ 14.8
Restricted Stock
       
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Share-based compensation (income) expense 6.0 6.2 9.2 12.0
Unrecognized share-based compensation cost $ 20.7   $ 20.7  
Equity instruments other than options expected to vest, Shares 2.4   2.4  
Equity instruments other than options expected to vest, weighted-average grant date fair value $ 11.95   $ 11.95  
Unrecognized compensation expense, weighted-average period of recognition     2 years 4 months 24 days