Commitments and Contingencies (Details) (USD $)	12 Months Ended
	Jul. 31, 2011	Jul. 31, 2010	Jul. 31, 2009
Major Operating and Capital Expenses [Abstract]
2012	$ 18,984,000
2012	231,000
2013	15,147,000
2013	204,000
2014	10,470,000
2014	182,000
2015	8,067,000
2016	6,175,000
Thereafter	37,029,000
Operating Leases, Future Minimum Payments Due	95,872,000
Capital Leases, Future Minimum Payments Due	617,000
Less amount representing interest	(36,000)
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments	581,000
Outstanding letters of credit	6,700,000
Legal Matters Estimate Of Possible Loss	2,000,000
Notice of proposed assessment for uncollected sales tax including interest and penalties	7,380,000
Environmental Matters Remedition expenses Reserves	3,000,000
Environmental Matters Cover Costs	200,000
Facilities Rental Expense
Major Operating and Capital Expenses [Abstract]
Rental expense	17,400,000	16,800,000	16,800,000
Yard Operations Equipment Rental Expense
Major Operating and Capital Expenses [Abstract]
Rental expense	$ 3,300,000	$ 4,100,000	$ 3,800,000