Long-Term Debt, Derivatives and Letters of Credit (Details 2) (Designated as Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified	Aug. 31, 2012	May 31, 2012
Fair value totals and balance sheet classification for derivatives designated as hedges
Fair value liability	$ 2,566	$ 2,678
Long-term Debt [Member] | Euro denominated long-term debt [Member]
Fair value totals and balance sheet classification for derivatives designated as hedges
Fair value liability	$ 2,566	$ 2,678