Goodwill, Service Contracts and Other Assets - Information Regarding Service Contracts and Other Assets (Details) - USD ($) $ in Thousands	May. 31, 2015	May. 31, 2014	May. 31, 2013
Information regarding service contracts and other assets
Service contracts, net	$ 42,434	$ 55,675	$ 92,153
Other assets, carrying amount	65,423	72,906
Other assets, accumulated amortization	47,929	53,280
Other assets, net	17,494	19,626
Noncompete and consulting agreements
Information regarding service contracts and other assets
Other assets, carrying amount	41,828	49,080
Other assets, accumulated amortization	40,379	47,036
Other assets, net	1,449	2,044
Other
Information regarding service contracts and other assets
Other assets, carrying amount	23,595	23,826
Other assets, accumulated amortization	7,550	6,244
Other assets, net	16,045	17,582
Service contracts
Information regarding service contracts and other assets
Service contracts, carrying amount	340,816	360,634
Service contracts, accumulated amortization	298,382	304,959
Service contracts, net	$ 42,434	$ 55,675