Derivative Instruments - Additional Information (Detail) - Forward Contracts - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017	Jul. 31, 2017
Derivative [Line Items]
Notional amount of cash flow hedge instruments	$ 11.7		$ 11.7		$ 10.9
Unrealized gain on cash flow hedges	0.4		0.4		0.5
Cost of Revenue and Operating Expenses
Derivative [Line Items]
Realized gains (losses) on cash flow hedge instruments	0.1	$ (0.2)	0.2	$ (0.3)
Designated as Hedging Instrument
Derivative [Line Items]
Derivative asset, current	$ 0.5		$ 0.5		$ 0.6