Fair Value of Option Grant Assumptions (Detail) (USD $)	3 Months Ended				6 Months Ended
	Jan. 31, 2014		Jan. 31, 2013		Jan. 31, 2014		Jan. 31, 2013
Stock Options
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected option term in years	0 years	[1]	5 years 4 months 17 days	[1]	5 years 4 months 13 days	[1]	5 years 4 months 28 days	[1]
Expected volatility			41.30%	[2]	38.60%	[2]	40.60%	[2]
Risk-free interest rate			0.75%	[3]	1.77%	[3]	0.78%	[3]
Expected annual dividend yield			0.54%	[4]	0.52%	[4]	0.57%	[4]
Total Shareholders Return
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Stock Price			$ 70.04	[5]	$ 77.08	[5]	$ 70.04	[5]
Expected volatility			28.00%	[6]	27.60%	[6]	28.00%	[6]
Risk-free interest rate			0.32%	[7]	0.82%	[7]	0.32%	[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 for periods equal to the expected term of the stock option is based on the U.S. Treasury yield curve in effect at the time of grant

[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 for periods equal to the performance period is based on the U.S. Treasury yield curve in effect at the time of grant.

[8] Dividends are considered reinvested when calculating TSR. The dividend yield is therefore considered to be 0%.