Fair Value of TSR Performance-Based Awards Valuation Assumption (Detail) - Restricted Stock Units (RSUs) - $ / shares
 3 Months Ended 9 Months Ended
Apr. 30, 2017
Apr. 30, 2016
Apr. 30, 2017
Apr. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock price [1] $ 73.60   $ 89.88 $ 84.06
Expected volatility [2] 27.00% 0.00% 27.00% 26.40%
Risk-free interest rate [3] 0.85% 0.00% 0.85% 1.04%
Expected annual dividend yield [4] 0.00% 0.00% 0.00% 0.00%
Time Based Restricted Stock Awards        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted average grant date fair value $ 78.22 $ 74.18 $ 88.16 $ 82.66
Performance Based Restricted Stock Awards        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Weighted average grant date fair value $ 73.60   $ 86.88 $ 98.81
[1] The stock price is the closing price of our common stock on the date of grant.
[2] 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.
[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 performance period.
[4] Dividends are considered reinvested when calculating TSR. The dividend yield is therefore considered to be 0%.