Schedule of Components of Total Current Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010
Income Taxes [Line Items]
Federal tax expense at statutory rates	$ 63,242	$ 53,420	$ 59,988
State tax expense at various state tax rates (net of federal benefit)	1,054	956	5,153
Current tax expense effect of accrued product warranties	2,371	1,698	3,622
Current tax expense effect of other temporary items	(270)	1,989	(407)
Federal income tax credits and incentives	(980)	(2,421)	(1,069)
Domestic production activities deduction	(5,645)	(5,236)	(3,745)
Executive compensation limitation	38		1,578
Change in uncertain tax positions	2,540	(1,426)	(1,931)
Adjustments to current tax payable	(301)	(1,169)	807
Other permanent items	345	1,382	792
Total current expense	$ 62,394	$ 49,193	$ 64,788