Property and Equipment (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012
Property, Plant and Equipment [Line Items]
Property and equipment	$ 541,718	$ 505,012
Less accumulated depreciation and amortization of property and equipment	171,965	156,948
Property and equipment, net	369,753	348,064
Depreciation and amortization expense of property and equipment	60,124	55,023	48,403
Land [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	1,942	1,983
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	33,996	35,216
Buildings [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Range of Useful Lives in Years	25 years	25 years
Buildings [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Range of Useful Lives in Years	30 years	30 years
Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	204,102	181,316
Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Range of Useful Lives in Years	2 years	2 years
Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Range of Useful Lives in Years	10 years	10 years
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	224,766	167,084
Software [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Range of Useful Lives in Years	5 years	5 years
Software [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Range of Useful Lives in Years	10 years	10 years
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	19,399	12,278
Leasehold improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Range of Useful Lives in Years	5 years	5 years
Leasehold improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Range of Useful Lives in Years	15 years	15 years
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	3,809	5,796
Furniture and fixtures [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Range of Useful Lives in Years	5 years	5 years
Furniture and fixtures [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Range of Useful Lives in Years	7 years	7 years
Work in progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	$ 53,704	$ 101,339