Goodwill, Service Contracts and Other Assets Narrative (Details) (USD $)	3 Months Ended
	Aug. 31, 2012	Aug. 31, 2011	May 31, 2012
Goodwill, Service Contracts and Other Assets [Abstract]
Cash surrender value of insurance policies	$ 59,300,000		$ 57,400,000
Equity method investments	31,500,000		31,900,000
Cost method investments	900,000		900,000
Amortization expense	6,100,000	10,233,000
Estimated amortization expense, year one	22,200,000
Estimated amortization expense, year two	18,100,000
Estimated amortization expense, year three	15,300,000
Estimated amortization expense, year four	10,100,000
Estimated amortization expense, year five	$ 5,100,000