Fair Value of Option Granted Valuation Assumption (Detail) - Stock Options - $ / shares		3 Months Ended	6 Months Ended
		Jan. 31, 2015	Jan. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected option term in years	[1]	5 years 3 months 22 days	5 years 3 months 22 days
Expected volatility	[2]	28.20%	29.30%
Risk-free interest rate	[3]	1.65%	1.82%
Expected annual dividend yield	[4]	0.54%	0.56%
Weighted average grant date fair value		$ 19.89	$ 19.95

[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.