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Schedule Of Estimated Fair Value Of Option Using Black-Scholes Option Pricing Model, Weighted Average Assumptions (Detail) (USD $)
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Stock Option
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Average risk free interest rate 0.80% 0.80% 0.90% 0.80%
Average expected term (in years) 4 years 4 months 24 days 4 years 3 months 18 days 4 years 7 months 6 days 4 years 6 months
Average expected volatility 31.00% 32.00% 29.00% 32.00%
Weighted average fair value at grant date $ 132.88 $ 149.90 $ 141.68 $ 143.50
Employee Stock Purchase Plan
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Average risk free interest rate     0.20% 0.20%
Average expected term (in years) 0 years 0 years 1 year 3 months 18 days 1 year 3 months 18 days
Average expected volatility     33.00% 32.00%
Weighted average fair value at grant date     $ 170.51 $ 133.75