Other Accrued Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Aug. 31, 2012	May 31, 2012
Summary of other accrued liabilities
Payroll and other compensation expenses	$ 21,416	$ 27,871
Insurance accruals	5,102	4,388
Property, sales and other non-income related taxes	2,009	1,966
Other	4,959	4,267
Total	$ 33,486	$ 38,492