Product Warranty Liability (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Oct. 31, 2012	Oct. 31, 2011
Product Liability Contingency [Line Items]
Balance at the beginning of the period	$ 5,634	$ 5,174
Accrual	1,284	1,962
Settlements made in cash or in kind during the period	(1,475)	(1,886)
Balance at the end of the period	$ 5,443	$ 5,250