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Share Based Compensation (Narrative) (Detail) (USD $)
In Millions, except Share data, 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]      
Shares authorized to issue grants 26,963,150 26,963,150 26,963,150
Options available for grant under the Plans 854,266    
Tax benefits recorded on stock based compensation $ 6.8 $ 7.2 $ 7.8
Aggregate intrinsic value of options exercisable $ 103.8    
Weighted average remaining contractual term of options exercisable (in years) 6 years 1 month 6 days    
Weighted-average remaining contractual life for options outstanding (in years) 7 years 4 months 24 days 7 years  
Minimum [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value of common stock to preferred stock, percentage 10.00%    
Period of vesting provisions (in years) 1 year    
Minimum [Member] | Stock Options [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Period of vesting provisions (in years) 1 year    
Minimum [Member] | Restricted Stock [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Period of vesting provisions (in years)   1 year  
Maximum [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value of common stock to preferred stock, percentage 25.00%    
Period of vesting provisions (in years) 6 years    
Maximum [Member] | Stock Options [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Period of vesting provisions (in years) 6 years    
Maximum [Member] | Restricted Stock [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Period of vesting provisions (in years)   6 years