Subsequent Event (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Aug. 31, 2013 Subsequent Event [Member]	Aug. 31, 2013 2013 Fixed Rate Notes [Member] Subsequent Event [Member]	May 31, 2013 2011 Fixed Rate Notes [Member]
Subsequent Event [Line Items]
Long-term debt		$ 155.0	$ 450.2
Senior secured notes interest rate, percentage		3.75%	5.40%
Expected life of debt instrument		7 years
Maturity date		2043
Proceeds from issuance of debt	$ 155.0