Accounts Payable and Accrued Liabilities (Details) (USD $) In Thousands	Jul. 31, 2011	Jul. 31, 2010
Payables and Accruals [Abstract]
Trade accounts payable	$ 12,365	$ 14,923
Accounts payable to sellers	42,190	40,370
Accrued insurance	5,494	4,831
Accrued compensation and benefits	15,605	14,298
Buyer prepayments	14,229	9,105
Other accrued liabilities	11,825	10,213
Accounts Payable and Accrued Liabilities, Current, Total	$ 101,708	$ 93,740