Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Aug. 31, 2017	Aug. 31, 2016
Earnings Per Share
Effect to the participating securities as result of net loss	$ 0.0
Basic and Diluted EPS:
Income from continuing operations	10.6	$ 9.9
Less income attributable to participating shares	(0.1)	(0.1)
Income from continuing operations attributable to common shareholders	10.5	9.8
Loss from discontinued operations attributable to common shareholders		(0.4)
Net income attributable to common shareholders for earnings per share	$ 10.5	$ 9.4
Weighted Average Shares:
Weighted average common shares outstanding - basic	34,000,000	33,900,000
Additional shares from assumed exercise of stock options	500,000	200,000
Weighted average common shares outstanding - diluted	34,500,000	34,100,000
Earnings per share - basic:
Earnings from continuing operations	$ 0.31	$ 0.29
Loss from discontinued operations		(0.01)
Earnings per share - basic	0.31	0.28
Earnings per share - diluted:
Earnings from continuing operations	0.31	0.29
Loss from discontinued operations		(0.01)
Earnings per share - diluted	$ 0.31	$ 0.28
Antidilutive stock options excluded from the computation of diluted earnings per share (in shares)		2,041,000