Share-based Compensation - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Oct. 31, 2014	Oct. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised	$ 0.1	$ 1.5
Total fair value of restricted stock grants vested in period	5.2	19.8
Stock Option and Restricted Stock Bonus Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to non-vested share-based compensation arrangements	$ 17.0
Unrecognized compensation cost related to non-vested share-based compensation arrangements, weighted average period	1 year 10 months 24 days
Time Based Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of awards granted	$ 71.09	$ 76.99
Non-GAAP EPS Performance-Based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, grants in period	34,850	35,562
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of awards granted	$ 19.95	$ 27.54
Total Shareholders Return
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, grants in period	27,065	27,355
Performance Based Restricted Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of awards granted	$ 78.25	$ 93.76