Property and Equipment (Details) - USD ($)	12 Months Ended
	May 31, 2016	May 31, 2015	May 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,413,572,000	$ 2,194,278,000
Less: accumulated depreciation	1,419,335,000	1,322,857,000
Property, plant and equipment, net	994,237,000	871,421,000
Capitalized interest	1,100,000	600,000	$ 0
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	117,881,000	116,172,000
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	509,316,000	501,742,000
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,584,478,000	1,446,041,000
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	28,530,000	26,023,000
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 173,367,000	$ 104,300,000