Property and Equipment, Net of Accumulated Depreciation (Narrative) (Details) $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended
	Sep. 30, 2017	Aug. 31, 2017 USD ($) ft² item	Nov. 30, 2017 USD ($)	Nov. 30, 2016 USD ($)	Nov. 30, 2017 USD ($)	Nov. 30, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Depreciation expense			$ 28.4	$ 25.5	$ 56.5	$ 50.8
Cost of building purchased					$ 95.5	$ 46.8
Multi-Building Campus [Member] | County Of Monroe Industrial Development Agency [Member]
Property, Plant and Equipment [Line Items]
Public benefits and inducements expiration date	Dec. 31, 2039
Multi-Building Campus [Member] | Rochester, NY [Member]
Property, Plant and Equipment [Line Items]
Number of buildings planned to be purchased | item		5
Renovation square feet | ft²		300,000
Estimated cost of buildings to be purchased and building renovations		$ 60.0
Cost of building purchased			34.7
Escrow for building renovations			$ 16.0