Schedule of Differences Between Income Taxes at Federal Statutory Rate and Actual Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2010
Reconciliation of Statutory Federal Tax Rate [Line Items]
Provision at federal statutory rate	$ 63,242	$ 53,420	$ 59,988
State and local income taxes (net of federal benefit)	975	978	5,124
Federal income tax credits and incentives	(980)	(2,421)	(1,069)
Domestic production activities deduction	(5,645)	(5,236)	(3,745)
Change in uncertain tax positions	1,619	(1,124)	(278)
Executive compensation limitation	38		1,578
Reduction of excess current tax payable and deferred tax liabilities	(642)	(645)	(1,061)
Other permanent Items	345	1,382	792
Income Taxes	$ 58,952	$ 46,354	$ 61,329