Derivative Instruments and Hedging Activities (Details 2) (Cash flow hedges, USD $) In Millions, unless otherwise specified	12 Months Ended
May 31, 2014	May 31, 2013	May 31, 2012
Cash flow hedges
Impact of the interest rate swap and interest cap agreement on the condensed consolidated statement of income
Amount of unrealized gain recorded in other accumulated comprehensive income (loss)	$ 0.7	$ 0.6	$ (3.9)

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration