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Primary Assumptions Valuation Market Component Awards (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Expected volatility 35.70% 39.50% 31.40%
Risk-free interest rate 0.87% 1.63% 1.88%
Dividend yield 0.00% 0.00% 0.00%
Restricted Stock Units With Market Based Performance Criteria
     
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Grant date fair value per share of Company common stock 58.63    
Expected volatility 36.44%    
Risk-free interest rate 0.47%    
Dividend yield 0.00%    
Performance vesting hurdle future fair value per share of Company common stock 85.00