Long-Term Debt, Derivatives and Letters of Credit (Details Textual) In Millions, unless otherwise specified	3 Months Ended			3 Months Ended
	Aug. 31, 2012 USD ($)	Aug. 31, 2012 Economic Hedge [Member] USD ($)	Aug. 31, 2012 Economic Hedge [Member] EUR (€)	Aug. 31, 2012 Line of Credit [Member]	Aug. 31, 2012 Standby Letters of Credit [Member] USD ($)	May 31, 2012 Standby Letters of Credit [Member] USD ($)
Line of Credit Facility [Line Items]
Interest based on variable euro dollar rate option				LIBOR plus 1.75% margin
Basis spread on LIBOR Rate				1.75%
Maturity period				July 2016
Borrowing under credit facility		$ 15.4	€ 12.3
Outstanding letter of credit					16.7	13.5
Long-Term Debt Derivatives and Letters of Credit (Textual) [Abstract]
Borrowing capacity	150
Debt issuance costs	$ 0.8