Goodwill and Intangible Assets, Net of Accumulated Amortization (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012
Goodwill and Intangible Assets, Net of Accumulated Amortization (Textual)
Goodwill	$ 540.3	$ 533.9
Amortization expense relating to intangible assets	$ 15.9	$ 19.0	$ 23.0
Finite-Lived Intangible Assets [Line Items]
Acquired intangible assets, Weighted average amortization period	7 years 3 months 19 days
Customer Lists [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired intangible assets, Weighted average amortization period	7 years 4 months 24 days
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired intangible assets, Weighted average amortization period	3 years