Product Warranty Liability (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013	Jan. 31, 2012
Product Liability Contingency [Line Items]
Balance at the beginning of the period	$ 5,443	$ 5,250	$ 5,634	$ 5,174
Accrual	1,595	1,867	2,879	3,829
Settlements made in cash or in kind during the period	(1,581)	(1,350)	(3,056)	(3,236)
Balance at the end of the period	$ 5,457	$ 5,767	$ 5,457	$ 5,767