Income Taxes The components of deferred income taxes included on the consolidated balance sheets (Details) (USD $) In Thousands, unless otherwise specified	May 31, 2012	May 31, 2011
Deferred tax assets:
Allowance for doubtful accounts	$ 5,577	$ 5,630
Inventory obsolescence	11,507	11,204
Insurance and contingencies	28,708	19,121
Stock-based compensation	16,017	12,585
Foreign tax credit carry-forward	9,054	0
Other	18,453	15,065
Deferred Tax Assets, Gross	89,316	63,605
Valuation reserve	(9,054)	0
Deferred Tax Assets, Net	80,262	63,605
Deferred tax liabilities:
In service inventory	64,061	10,108
Property	122,675	118,413
Intangibles	88,696	77,910
State taxes and other	11,970	7,682
Deferred tax liabilities	287,402	214,113
Net deferred tax liability	$ 207,140	$ 150,508