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Stock-Based Compensation Plans and Arrangements - Restricted Stock and Performance Stock Unit Activity (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized compensation cost $ 18.0    
Weighted average period for total unrecognized compensation cost 1 year 9 months 18 days    
Restricted Stock [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total fair value of shares vested 4 6 9
Unrecognized compensation cost 0.2    
Weighted average period for total unrecognized compensation cost 9 months 18 days    
Restricted Stock Units and Performance Stock Units [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized compensation cost 14.0    
Weighted average period for total unrecognized compensation cost 1 year 10 months 24 days    
Total fair value of restricted stock units that vested and converted to common stock $ 13.0 $ 0.4 $ 0.4