Goodwill, Service Contracts and Other Assets (Details 3) (USD $)	9 Months Ended
	Feb. 29, 2012	Feb. 28, 2011	May 31, 2011
Information regarding service contracts and other assets
Other Assets, Carrying Amount	$ 190,447,000		$ 183,423,000
Other Assets, Accumulated Amortization	74,981,000		68,672,000
Other Assets, Net	115,466,000		114,751,000
Investments
Cash surrender value of insurance policies	58,100,000		51,100,000
Equity method investments	32,700,000		30,200,000
Cost method investments	800,000		2,900,000
Amortization
Amortization expense	29,520,000	32,166,000
Estimated amortization expense, year one	38,100,000
Estimated amortization expense, year two	21,500,000
Estimated amortization expense, year three	18,100,000
Estimated amortization expense, year four	15,200,000
Estimated amortization expense, year five	9,800,000
Noncompete agreements
Information regarding service contracts and other assets
Other Assets, Carrying Amount	76,231,000		76,091,000
Other Assets, Accumulated Amortization	69,076,000		63,982,000
Other Assets, Net	7,155,000		12,109,000
Investments
Information regarding service contracts and other assets
Other Assets, Carrying Amount	91,638,000		84,197,000
Other Assets, Net	91,638,000		84,197,000
Other
Information regarding service contracts and other assets
Other Assets, Carrying Amount	22,578,000		23,135,000
Other Assets, Accumulated Amortization	5,905,000		4,690,000
Other Assets, Net	16,673,000		18,445,000
Service Contracts
Information regarding service contracts and other assets
Service contracts, Carrying Amount	382,835,000		379,967,000
Service contracts, Accumulated Amortization	301,169,000		277,655,000
Service contracts, Net	$ 81,666,000		$ 102,312,000