Change in Product Warranty Liability (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jan. 31, 2013	Jan. 31, 2012
Product Information [Line Items]
Balance at beginning of period	$ 1,672	$ 2,281
Warranty expenditures for current period	(2,025)	(1,783)
Changes in liability related to pre-existing warranties	(33)	20
Provision for warranty costs in the period	1,644	887
Balance at end of period	$ 1,258	$ 1,405