Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details) $ in Millions		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 28, 2018 USD ($)	Mar. 31, 2018 USD ($)	Feb. 28, 2018 USD ($)	Feb. 28, 2017 USD ($)	Feb. 28, 2018 USD ($) segment	Feb. 28, 2017 USD ($)	May 31, 2017 USD ($)
Accounting Policies [Line Items]
Number of reportable segments | segment					1
Other current liabilities related to termination of license agreements	$ 32.6		$ 32.6		$ 32.6
Cost related to termination of license agreement			24.7
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			$ 10.3	$ 8.9	$ 29.4	$ 26.5
Subsequent Event [Member]
Accounting Policies [Line Items]
Cost expected to acquire rights to client lists		$ 30.0
Europe [Member] | Revenue [Member] | Geographic Concentration Risk [Member]
Accounting Policies [Line Items]
Total percentage			1.00%	1.00%	1.00%	1.00%
Europe [Member] | Long Lived Assets [Member] | Geographic Concentration Risk [Member]
Accounting Policies [Line Items]
Total percentage	13.00%