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Summary of Stock Option Activity (Detail) (Stock Option, USD $)
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Stock Option
   
Options Outstanding Number of Shares    
Outstanding at beginning of period 4,350,631  
Granted 12,450  
Exercised (256,255)  
Forfeited (167,041)  
Outstanding at end of period 3,939,785  
Exercisable at end of period 2,390,668  
Weighted Average Exercise Price    
Outstanding at beginning of period $ 23.01  
Granted $ 31.49  
Exercised $ 18.97  
Forfeited $ 24.78  
Outstanding at end of period $ 23.22  
Exercisable at end of period $ 24.32  
Weighted Average Fair Value    
Outstanding at beginning of period $ 9.17  
Granted $ 11.76 $ 8.20
Exercised $ 7.71  
Forfeited $ 9.80  
Outstanding at end of period $ 9.25  
Exercisable at end of period $ 9.21  
Weighted Average Remaining Contractual Life    
Outstanding at end of period 4 years 6 months 7 days  
Exercisable at end of period 3 years 4 months 24 days