Property and Equipment (Details) - USD ($)	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,194,278,000	$ 2,143,663,000
Less: accumulated depreciation	1,322,857,000	1,287,961,000
Property, plant and equipment, net	871,421,000	855,702,000
Capitalized interest	600,000	0	$ 0
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	116,172,000	116,989,000
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	501,742,000	521,113,000
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,446,041,000	1,427,356,000
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	26,023,000	35,821,000
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 104,300,000	$ 42,384,000