Long-Term Debt, Derivatives and Letters of Credit - Additional Information (Detail) In Millions, unless otherwise specified	9 Months Ended			9 Months Ended
	Feb. 28, 2013 USD ($)	Feb. 28, 2013 Economic Hedge USD ($)	Feb. 28, 2013 Economic Hedge EUR (€)	Feb. 28, 2013 Line of Credit	Feb. 28, 2013 Standby Letters of Credit USD ($)	May 31, 2012 Standby Letters of Credit USD ($)
Line of Credit Facility [Line Items]
Borrowing capacity	$ 150
Interest based on variable euro dollar rate option				LIBOR plus 1.75% margin
Basis spread on LIBOR Rate				1.75%
Maturity period				July 2016
Debt issuance costs	0.8
Borrowing under credit facility		16.1	12.3
Outstanding letter of credit					$ 15.3	$ 13.5