Stock-Based Compensation (Tables)

6 Months Ended

Nov. 30, 2014

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan

The following table summarizes stock-based compensation expense included in Selling, general and administrative expenses for the periods indicated: 

	Three months ended   November 30,				Six months ended   November 30,
	2014		2013		2014		2013
Stock option expense	$	3.8	$	4.4	$	4.6	$	4.6
Restricted stock unit expense	0.6		1.2		1.3		1.9
Management stock purchase plan	0.6		0.0		0.6		0.1
Employee stock purchase plan	0.1		0.0		0.1		0.1
Total stock-based compensation expense	$	5.1	$	5.6	$	6.6	$	6.7