Summary of Charges Related to Accrued Restructuring Activities (Detail) - USD ($) $ in Millions		3 Months Ended	6 Months Ended
		Jan. 31, 2018	Jan. 31, 2018
Restructuring Cost and Reserve [Line Items]
Balance at beginning period		$ 1.4	$ 2.8
Restructuring charge		0.2	0.9
Adjustments			(0.2)
Cash payments		(0.8)	(2.6)
Non-cash adjustments		0.3	0.2
Balance at end period		1.1	1.1
Employee Severance and Benefits
Restructuring Cost and Reserve [Line Items]
Balance at beginning period	[1]	1.1	2.7
Restructuring charge	[1]	0.2	0.6
Adjustments	[1]		(0.2)
Cash payments	[1]	(0.8)	(2.6)
Non-cash adjustments	[1]	0.3	0.3
Balance at end period	[1]	0.8	0.8
Facility Exit Costs
Restructuring Cost and Reserve [Line Items]
Balance at beginning period	[1]	0.3	0.1
Restructuring charge	[1]		0.3
Non-cash adjustments	[1]		(0.1)
Balance at end period	[1]	$ 0.3	$ 0.3

[1] Restructuring charges in fiscal year 2018 relate to the Fiscal Year 2017 Restructuring Plan.