Fair Value of Option Grant Assumptions (Detail) (USD $)	12 Months Ended
	Jul. 31, 2012		Jul. 31, 2011		Jul. 31, 2010
Stock Options
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected option term	5 years 3 months 26 days	[1]	4 years 8 months 27 days	[1]	4 years 10 months 2 days	[1]
Expected volatility factor	42.00%	[2]	43.00%	[2]	43.00%	[2]
Risk-free interest rate	0.95%	[3]	1.18%	[3]	2.20%	[3]
Expected annual dividend yield	0.90%	[4]	1.00%	[4]	1.00%	[4]
Total Shareholders Return
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Stock Price	57.81	[5]	41.96	[5]	40.06	[5]
Expected volatility factor	29.00%	[6]	49.00%	[6]	51.00%	[6]
Risk-free interest rate	0.33%	[7]	0.73%	[7]	1.19%	[7]
Expected annual dividend yield	0.00%	[8]	0.00%	[8]	0.00%	[8]
Employee Stock Purchase Plan
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected option term	6 months		6 months		6 months
Expected volatility factor	42.00%		42.00%		50.00%
Risk-free interest rate	0.79%		0.27%		2.58%
Expected annual dividend yield	1.00%		1.00%		1.10%

[1] The option life was determined by estimating the expected option life, using historical data.

[2] The stock volatility for each grant is determined based on the review of the experience of the weighted average of historical daily price changes of the Company's common stock over the most recent five years, which approximates the expected option life of the grant.

[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 weighted average closing price of the Company's common stock on the dates of grant.

[6] The stock volatility for each grant is determined based on the historical volatility for the peer group companies 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%.