Derivative Instruments and Hedging Activities (Details) (USD $) In Millions, unless otherwise specified	Aug. 31, 2012	May 31, 2012
Derivative Instruments and Hedging Activities
Number of derivative financial instruments	2
Interest rate cap | Derivatives designated as hedging instruments:
Derivative Instruments and Hedging Activities
Notional amount under revolving credit agreement	$ 50
Fair value carrying amount of the Company's interest rate derivatives
Derivative Assets	0.2	0.2
Interest rate swap | Derivatives designated as hedging instruments:
Derivative Instruments and Hedging Activities
Notional amount under revolving credit agreement	50
Fair value carrying amount of the Company's interest rate derivatives
Derivative Liabilities	$ (5.0)	$ (4.5)