Derivative Instruments - Additional Information (Detail) - Forward Contracts - USD ($) $ in Millions	3 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Jul. 31, 2017
Derivative [Line Items]
Notional amount of cash flow hedge instruments	$ 11.3		$ 10.9
Unrealized gain on cash flow hedges	0.1		0.5
Cost of Revenue and Operating Expenses
Derivative [Line Items]
Realized gains (losses) on cash flow hedge instruments	0.2	$ (0.1)
Designated as Hedging Instrument
Derivative [Line Items]
Derivative asset, current	$ 0.1		$ 0.6