Stock-Based Compensation (Tables)

9 Months Ended

Feb. 28, 2015

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   February 28,				Nine months ended   February 28,
	2015		2014		2015		2014
Stock option expense	$	0.8	$	0.8	$	5.4	$	5.4
Restricted stock unit expense	0.6		0.2		1.9		2.1
Management stock purchase plan	0.1		0.0		0.7		0.1
Employee stock purchase plan	0.1		0.1		0.2		0.2
Total stock-based compensation expense	$	1.6	$	1.1	$	8.2	$	7.8