Stock-Based Compensation (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2018	Nov. 30, 2017	Nov. 30, 2018	Nov. 30, 2017
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	$ 3.7	$ 6.0	$ 5.2	$ 7.5
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	0.2	0.1	0.3	0.2
Stock option expense
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	$ 2.8	$ 4.6	$ 3.6	$ 5.4
Restricted stock unit expense
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	0.7	0.8	1.3	1.4
Management stock purchase plan
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	0.2	0.6	0.2	0.6
Employee stock purchase plan
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	$ 0.0	$ 0.0	$ 0.1	$ 0.1