Change in Product Warranty Liability (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Product Information [Line Items]
Balance at beginning of period	$ 3,610	$ 2,725
Warranty expenditures for current period	(1,990)	(1,865)
Changes in liability related to pre-existing warranties	129	(31)
Provision for warranty costs in the period	2,123	1,702
Balance at end of period	$ 3,872	$ 2,531