Share-based Compensation - Additional Information (Detail) (USD $)	3 Months Ended				12 Months Ended			3 Months Ended		3 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2013 Total Shareholders Return	Oct. 31, 2012 Total Shareholders Return	Jul. 31, 2013 Total Shareholders Return Y	Jul. 31, 2012 Total Shareholders Return Y	Jul. 31, 2014 Future Period Total Shareholders Return Y	Oct. 31, 2013 Performance Based Restricted Share Awards	Oct. 31, 2012 Performance Based Restricted Share Awards	Oct. 31, 2013 Performance Based Restricted Share Awards Minimum	Oct. 31, 2013 Performance Based Restricted Share Awards Maximum	Oct. 31, 2013 Performance Based Restricted Share Awards Total Shareholders Return	Oct. 31, 2013 Performance Based Restricted Share Awards Earnings Per Share	Oct. 31, 2013 Performance Based Restricted Stock and Restricted Stock Units	Oct. 31, 2013 Performance Based Restricted Stock and Restricted Stock Units Total Shareholders Return	Oct. 31, 2013 Performance Based Restricted Stock and Restricted Stock Units Earnings Per Share
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted	107,767	97,300
Share based compensation expense, service period					2.8	2.8	2.8
Weighted average grant date fair values of restricted stock units granted			$ 115.45	$ 106.36
Restricted stock units granted during period								189,039	326,585					189,039	86,857	102,182
Share based compensation performance period								3 years
Share based compensation target award percentage										0.00%	200.00%
Restricted stock units granted during period												27,355	35,562