Stock-Based Compensation (Details) - Schedule of stock-based compensation (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Aug. 31, 2014	Aug. 31, 2013
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Share-based payment awards, options, by number of shares issued from Treasury Stock	0.5	0.4
Stock option expense	$ 0.8	$ 0.2
Restricted stock unit expense	0.7	0.8
Stock-based compensation expense	1.6	1.1
Management Stock Purchase Plan
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	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