Stock-Based Compensation (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Aug. 31, 2018	Aug. 31, 2017
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	$ 1.5	$ 1.5
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	0.1	0.1
Stock option expense
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	$ 0.8	$ 0.8
Restricted stock unit expense
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	0.6	0.6
Management stock purchase plan
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	0.0	0.0
Employee stock purchase plan
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	$ 0.1	$ 0.1