Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Aug. 31, 2015	Aug. 31, 2014
Earnings per Share
Effect to the participating securities as result of net loss	$ 0.0
Antidilutive stock options excluded from the computation of diluted earnings per share (in shares)	148,163	180,163
Basic EPS:
Income from continuing operations	$ 8.2	$ 11.8
Less income attributable to participating shares	(0.2)	(0.2)
Income from continuing operations attributable to common shareholders	8.0	11.6
Income from discontinued operations attributable to common shareholders	14.7	2.6
Net income attributable to common shareholders for earnings per share - basic	22.7	14.2
Diluted EPS:
Income from continuing operations	8.2	11.8
Less income attributable to participating shares	(0.2)	(0.2)
Income from continuing operations attributable to common shareholders	8.0	11.6
Income from discontinued operations attributable to common shareholders	14.7	2.6
Net income attributable to common shareholders for earnings per share - diluted	$ 22.7	$ 14.2
Weighted average common shares outstanding - basic	34,700,000	38,800,000
Additional shares from the assumed exercise of stock options	400,000	400,000
Weighted average common shares outstanding - diluted	35,100,000	39,200,000
Earnings per share - basic:
Earnings from continuing operations	$ 0.23	$ 0.29
Earnings from discontinued operations	0.42	0.07
Earnings per share - basic	0.65	0.36
Earnings per share - diluted:
Earnings from continuing operations	0.23	0.29
Earnings from discontinued operations	0.42	0.07
Earnings per share - diluted	$ 0.65	$ 0.36