Share-based Compensation Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense before tax	$ 2.6	$ 1.8	$ 4.2	$ 4.2
Income tax effect	(0.8)	(0.5)	(1.3)	(1.2)
Share-based compensation expense included in net income	1.8	1.3	2.9	3.0
Product
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense before tax	0.1	0.1	0.2	0.3
Engineering
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense before tax	0.1	0.1	0.1	0.1
Research and Product Development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense before tax	0.5	0.6	0.9	1.1
Selling and Marketing
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense before tax	0.5	0.3	0.9	0.7
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation expense before tax	$ 1.4	$ 0.7	$ 2.2	$ 2.0