Stock-Based Compensation (Tables)

6 Months Ended

Nov. 30, 2017

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,
	2017		2016		2017		2016
Stock option expense	$	4.6	$	4.3	$	5.4	$	5.1
Restricted stock unit expense	0.8		0.7		1.4		1.4
Management stock purchase plan	0.6		0.4		0.6		0.4
Employee stock purchase plan	0.0		0.1		0.1		0.2
Total stock-based compensation expense	$	6.0	$	5.5	$	7.5	$	7.1

Schedule of Shares Issued Pursuant to Share-based Compensation Activity

The following table sets forth Common Stock issued pursuant to stock-based compensation plans as of the dates indicated:

	Three months ended November 30,		Six months ended November 30,
	2017	2016	2017	2016
Common Stock issued pursuant to stock-based compensation plans (in millions)	0.1	0.1	0.2	0.3