Summary of Significant Accounting Policies (Details 3) (USD $)	12 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010
Performance Based Options [Member]
Stock Option Assumptions
Expected term (in years)	6 years 6 months 26 days	6 years 6 months 26 days	6 years 6 months 26 days
Expected volatility	39.21%	39.39%	38.72%
Expected dividend yield	1.99%	1.96%	3.02%
Risk-free interest rate	2.05%	2.35%	3.03%
Weighted-average market value of underlying stock at grant date	$ 29.55	$ 28.43	$ 28.73
Weighted average exercise price	$ 29.55	$ 28.35	$ 29.78
Weighted average fair value of options granted	$ 10.01	$ 9.87	$ 8.70
Service Based Options [Member]
Stock Option Assumptions
Expected term (in years)	5 years 10 months 14 days	5 years 10 months 28 days	5 years 11 months 9 days
Expected volatility	39.41%	40.22%	39.88%
Expected dividend yield	2.07%	1.94%	3.01%
Risk-free interest rate	1.16%	1.65%	2.63%
Weighted-average market value of underlying stock at grant date	$ 27.05	$ 29.13	$ 28.68
Weighted average exercise price	$ 27.05	$ 29.13	$ 28.68
Weighted average fair value of options granted	$ 8.42	$ 9.59	$ 8.77