Stock-Based Compensation (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2019	Nov. 30, 2018
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	$ 0.9	$ 3.7	$ 2.4	$ 5.2
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	0.1	0.2	0.1	0.3
Stock option expense
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	$ 0.4	$ 2.8	$ 1.0	$ 3.6
Restricted stock unit expense
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	0.4	0.7	1.2	1.3
Management stock purchase plan
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	0.0	0.2	0.0	0.2
Employee stock purchase plan
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	$ 0.1	$ 0.0	$ 0.2	$ 0.1