Fair Value of Option Grant Assumptions (Detail) (USD $)	3 Months Ended
	Oct. 31, 2013		Oct. 31, 2012
Stock Options
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected option term	5 years 4 months 13 days	[1]	5 years 5 months 1 day	[1]
Expected volatility	38.60%	[2]	41.00%	[2]
Risk-free interest rate	1.77%	[3]	0.78%	[3]
Expected annual dividend yield	0.52%	[4]	0.57%	[4]
Weighted average grant date fair value	$ 27.54		$ 24.77
Total Shareholders Return
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Stock Price	$ 77.08	[5]	$ 70.04	[5]
Expected volatility	27.60%	[6]	28.00%	[6]
Risk-free interest rate	0.82%	[7]	0.32%	[7]
Expected annual dividend yield	0.00%	[8]	0.00%	[8]

[1] The expected option term factor was estimated using historical data.

[2] The expected volatility factor for each grant is determined based on the review of the average of historical daily price changes of our common stock over the most recent 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 factor 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. For the purpose of the fair value model, the dividend yield is therefore considered to be 0%.