Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Nov. 30, 2017 USD ($)	Nov. 30, 2016 USD ($)	Nov. 30, 2017 USD ($) segment	Nov. 30, 2016 USD ($)	May 31, 2017 USD ($)
Accounting Policies [Line Items]
Number of reportable segments | segment			1
Maximum individual workers' compensation claims liability			$ 1.3		$ 1.3
Maximum individual health insurance claims liability			0.3		$ 0.3
Stock-based compensation costs recognized	$ 10.4	$ 8.5	$ 19.1	$ 17.6
Germany [Member] | Total Revenue [Member] | Geographic Concentration Risk [Member]
Accounting Policies [Line Items]
Percentage of total revenue less than one percent			1.00%	1.00%