Stock-Based Compensation (Details) - Schedule of stock-based compensation (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2013	Nov. 30, 2012	Nov. 30, 2013	Nov. 30, 2012
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock option expense	$ 4.4	$ 0.6	$ 4.6	$ 1.6
Restricted stock unit expense	1.2	0.8	1.9	1.8
Stock-based compensation expense	5.6	2.1	6.7	4.2
Management Stock Purchase Plan [Member]
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	0	0.6	0.1	0.6
Employee Stock Purchase Plan [Member]
Stock-Based Compensation (Details) - Schedule of stock-based compensation [Line Items]
Stock-based compensation expense	$ 0	$ 0.1	$ 0.1	$ 0.2