Share-based Compensation Expense - Additional Information (Detail) - USD ($) $ in Millions		12 Months Ended
	Nov. 04, 1985	Jul. 31, 2015	Jul. 31, 2014	Jul. 31, 2013	Jan. 21, 2014	Jan. 23, 2012	Jan. 29, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised		$ 4.3	$ 1.9	$ 1.5
Cash received from exercise of options		7.3	4.9	3.4
Total fair value of restricted stock grants vested in period		9.8	24.9	16.0
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Tax benefit realized for tax deduction from option exercises		0.1	$ 0.1	$ 0.1
2009 Stock Incentive 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
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		$ 10.3
Unrecognized compensation cost related to non-vested share-based compensation arrangements, weighted average period		1 year 3 months 18 days
Total Shareholders Return Performance-based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, grants in period		28,455	27,450	24,470
Non-GAAP EPS Performance-Based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, grants in period		36,641	35,686	31,806
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares authorized to be granted	700,000
Share-based compensation arrangement by share-based payment award, purchase price of common stock, percent	85.00%