Share-based Compensation Expense - Additional Information (Detail) (USD $)	3 Months Ended			12 Months Ended			3 Months Ended		3 Months Ended			3 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2012 Total Shareholders Return	Jul. 31, 2012 Total Shareholders Return Y	Jul. 31, 2011 Total Shareholders Return Y	Jul. 31, 2013 Subsequent Event Total Shareholders Return Y	Oct. 31, 2012 Performance Based Restricted Stock Units	Oct. 31, 2011 Performance Based Restricted Stock Units	Oct. 31, 2012 Performance Based Restricted Stock Units Minimum	Oct. 31, 2012 Performance Based Restricted Stock Units Maximum	Oct. 31, 2012 Performance Based Restricted Stock and Restricted Stock Units	Oct. 31, 2012 Performance Based Restricted Stock and Restricted Stock Units Earnings Per Share	Oct. 31, 2012 Performance Based Restricted Stock and Restricted Stock Units Total Shareholders Return
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-qualified stock options granted	97,300
Weighted Average Grant Date Fair Value of Options Granted	$ 24.77	$ 16.36
Restricted stock units outstanding							326,585	407,137			326,585	194,964	131,621
Share based compensation performance period							3 years
Share based compensation target award percentage									0.00%	200.00%
Restricted stock units granted during period												30,474	23,668
Share based compensation expense, service period				2.7	2.7	2.7
Weighted average grant date fair value of restricted stock units granted			$ 106.36