Derivative Instruments and Hedging Activities (Details 2) (Cash flow hedges, USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
	Feb. 29, 2012	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 pre-tax loss recorded in accumulated other comprehensive income (loss)	$ (937)	$ (5,146)
Minimal gain or loss to be reclassified into earnings within the next 12 months