Share-based Compensation Expense - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended						12 Months Ended																		0 Months Ended
	Jul. 31, 2014	Jul. 31, 2013	Jul. 31, 2012	Jan. 21, 2014 2009 Stock Incentive Plan	Jan. 23, 2012 2009 Stock Incentive Plan	Jan. 29, 2010 2009 Stock Incentive Plan	Jul. 31, 2014 Stock Option and Restricted Stock Bonus Plans	Jul. 31, 2013 Maximum	Jul. 31, 2012 Maximum	Jul. 31, 2014 Time Based Restricted Stock Awards	Jul. 31, 2013 Time Based Restricted Stock Awards	Jul. 31, 2012 Time Based Restricted Stock Awards	Jul. 31, 2014 Non-GAAP EPS Performance-Based Awards	Jul. 31, 2013 Non-GAAP EPS Performance-Based Awards	Jul. 31, 2012 Non-GAAP EPS Performance-Based Awards	Jul. 31, 2014 Stock Options	Jul. 31, 2013 Stock Options	Jul. 31, 2012 Stock Options	Jul. 31, 2014 Total Shareholders Return	Jul. 31, 2013 Total Shareholders Return	Jul. 31, 2012 Total Shareholders Return	Jul. 31, 2014 Performance Based Restricted Stock Awards	Jul. 31, 2013 Performance Based Restricted Stock Awards	Jul. 31, 2012 Performance Based Restricted Stock Awards	Nov. 04, 1985 Employee Stock Purchase Plan	Nov. 04, 1985 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares authorized to be granted				4,453,518	2,200,000	1,600,000																				700,000
Unrecognized compensation cost related to non-vested share-based compensation arrangements							$ 10.4
Unrecognized compensation cost related to non-vested share-based compensation arrangements, weighted average period							1 year 3 months 18 days
Weighted average grant date fair value of awards granted										$ 82.46	$ 71.78	$ 50.45				$ 27.55	$ 25.25	$ 16.71				$ 93.85	$ 85.94	$ 77.59
Intrinsic value of options exercised	1.9	1.5	0.5
Cash received from exercise of options	4.9	3.4	1.9
Tax benefit realized for tax deduction from option exercises	0.1							0.1	0.1
Options, grants in period													35,686	31,806	38,042				27,450	24,470	38,042
Total fair value of restricted stock grants vested in period	$ 24.9	$ 16.0	$ 1.9
Share-based compensation arrangement by share-based payment award, purchase price of common stock, percent																									85.00%