Other Income (Expense) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Component Of Other Expense Income Nonoperating [Line Items]
Interest expense		$ 3.2	$ 0.6
Foreign exchange (losses)	$ (0.1)	$ (2.7)	$ (0.4)
Cash Deposits and Marketable Securities
Component Of Other Expense Income Nonoperating [Line Items]
Interest income	$ 0.6