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Fair Value of Option Grant Assumptions (Detail) (USD $)
 12 Months Ended
Jul. 31, 2014
Jul. 31, 2013
Jul. 31, 2012
Stock Options
      
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Expected option term in years 5 years 4 months 13 days [1] 5 years 5 months 1 day [1] 5 years 3 months 26 days [1]
Expected volatility 38.60% [2] 41.00% [2] 42.00% [2]
Risk-free interest rate 1.77% [3] 0.80% [3] 0.95% [3]
Expected annual dividend yield 0.52% [4] 0.57% [4] 0.90% [4]
Total Shareholders Return
      
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Stock Price $ 77.14 [5] $ 70.04 [5] $ 57.81 [5]
Expected volatility 27.60% [6] 28.00% [6] 29.00% [6]
Risk-free interest rate 0.82% [7] 0.32% [7] 0.33% [7]
Expected annual dividend yield 0.00% [8] 0.00% [8] 0.00% [8]
[1] The expected option term was estimated using historical data.
[2] The expected volatility for each grant is determined based on the review of the average of historical daily price changes of our common stock over the expected option term.
[3] The risk-free interest rate is determined based on the yield of zero-coupon U.S. Treasury securities for a period that is commensurate with the expected term assumption.
[4] The expected annual dividend yield is calculated by dividing the expected annual dividends by the stock price on the date of grant.
[5] The stock price is the closing price of our common stock on the date of grant.
[6] The expected volatility for each grant is determined based on the historical volatility for the peer group companies and our common stock over a period equal to the remaining term of the performance period from the date of grant for all awards.
[7] The risk-free interest rate is determined based on the yield of zero-coupon U.S. Treasury securities for a period that is commensurate with the performance period.
[8] Dividends are considered reinvested when calculating TSR. The dividend yield is therefore considered to be 0%.