Derivative Instruments and Hedging Activities (Details 2) (Cash flow hedges, USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Nov. 30, 2011	Nov. 30, 2011
Cash flow hedges
Impact of the interest rate swap and interest cap agreement on the condensed consolidated statement of income
Gain (loss) recognized in other comprehensive income - effective portion	$ (221)	$ (2,736)
Minimal gain or loss to be reclassified into earnings within the next 12 months