Property and Equipment (Details) (USD $) In Thousands, unless otherwise specified	May 31, 2012	May 31, 2011	May 31, 2010
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	$ 2,163,285	$ 2,042,396
Less: accumulated depreciation	1,218,980	1,096,178
Property and equipment, at cost, net	944,305	946,218
Land [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	104,850	103,838
Buildings and Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	492,293	484,254
Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	1,478,270	1,334,943
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	25,502	21,763
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, Gross	62,370	97,598
Capitalized Interest Costs [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, at cost, net	$ 1,300	$ 2,200	$ 2,200