Quarterly report pursuant to Section 13 or 15(d)

Goodwill and Intangible Assets, Net of Accumulated Amortization (Details Textuals)

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Goodwill and Intangible Assets, Net of Accumulated Amortization (Details Textuals) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Nov. 30, 2011
Nov. 30, 2010
Nov. 30, 2011
Nov. 30, 2010
May 31, 2011
Goodwill and Intangible Assets, Net of Accumulated Amortization (Textuals) [Abstract]          
Goodwill $ 513.6   $ 513.6   $ 513.7
Amortization expense $ 5.7 $ 4.6 $ 11.4 $ 9.3