Change in Product Warranty Liability (Detail) - USD ($) $ in Thousands	9 Months Ended
	Apr. 30, 2018	Apr. 30, 2017
Product Information [Line Items]
Balance at beginning of period	$ 3,610	$ 2,725
Warranty expenditures for current period	(3,224)	(2,778)
Changes in liability related to pre-existing warranties	114	(14)
Provision for warranty costs in the period	3,486	3,243
Balance at end of period	$ 3,986	$ 3,176