Stock-Based Compensation (Details)	3 Months Ended
	Oct. 31, 2011 Year	Oct. 31, 2010 Year
Performance Based Options [Member]
Stock Option Assumptions
Expected term (in years)	6.57	6.57
Expected volatility	39.21%	39.39%
Expected dividend yield	1.99%	1.96%
Risk-free interest rate	2.05%	2.35%
Weighted-average market value of underlying stock at grant date	29.55	28.35
Weighted average exercise price	29.55	28.35
Weighted-average fair value of options granted during the period	10.01	9.82
Service Based Options [Member]
Stock Option Assumptions
Expected term (in years)	5.89	5.92
Expected volatility	39.40%	40.22%
Expected dividend yield	2.07%	1.94%
Risk-free interest rate	1.16%	1.65%
Weighted-average market value of underlying stock at grant date	27.00	29.09
Weighted average exercise price	27.00	29.09
Weighted-average fair value of options granted during the period	8.37	9.58