Derivative Instruments and Hedging Activities (Details 2) (Cash flow hedges, USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Feb. 28, 2013	Feb. 29, 2012	Feb. 28, 2013	Feb. 29, 2012
Cash flow hedges
Impact of the interest rate swap and interest cap agreement on the condensed consolidated statement of income
Amount of unrealized loss recorded in other accumulated comprehensive income (loss)	$ 0.4	$ (0.9)	$ 0	$ (5.1)