Goodwill, Service Contracts and Other Assets - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Aug. 31, 2016	Aug. 31, 2015
Goodwill [Line Items]
Amortization expense for continuing operations	$ 3.5	$ 3.6
Estimated amortization expense, year one	14.7
Estimated amortization expense, year two	12.6
Estimated amortization expense, year three	12.1
Estimated amortization expense, year four	11.6
Estimated amortization expense, year five	$ 9.7