Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2015	Nov. 30, 2014	Nov. 30, 2015	Nov. 30, 2014
Earnings per Share
Effect to the participating securities as result of net loss			$ 0.0
Basic EPS:
Income from continuing operations	$ 10.4	$ 13.9	18.6	$ 25.7
Less income attributable to participating shares	(0.1)	(0.3)	(0.2)	(0.5)
Income from continuing operations attributable to common shareholders	10.3	13.6	18.4	25.2
Income (Loss) from discontinued operations attributable to common shareholders	(2.4)	1.3	12.3	3.9
Net income attributable to common shareholders for earnings per share - basic	7.9	14.9	30.7	29.1
Diluted EPS:
Income from continuing operations	10.4	13.9	18.6	25.7
Less income attributable to participating shares	(0.1)	(0.3)	(0.2)	(0.5)
Income from continuing operations attributable to common shareholders	10.3	13.6	18.4	25.2
Income (Loss) from discontinued operations attributable to common shareholders	(2.4)	1.3	12.3	3.9
Net income attributable to common shareholders for earnings per share - diluted	$ 7.9	$ 14.9	$ 30.7	$ 29.1
Weighted Average Shares:
Weighted average common shares outstanding - basic	34,400,000	38,700,000	34,600,000	38,700,000
Additional shares from the assumed exercise of stock options	200,000	400,000	300,000	500,000
Weighted average common shares outstanding - diluted	34,600,000	39,100,000	34,900,000	39,200,000
Earnings per share - basic:
Earnings from continuing operations	$ 0.30	$ 0.35	$ 0.53	$ 0.65
Earnings (Loss) from discontinued operations	(0.07)	0.03	0.36	0.10
Earnings per share - basic	0.23	0.38	0.89	0.75
Earnings per share - diluted:
Earnings from continuing operations	0.30	0.35	0.53	0.65
Earnings (Loss) from discontinued operations	(0.07)	0.03	0.36	0.10
Earnings per share - diluted	$ 0.23	$ 0.38	$ 0.89	$ 0.75
Antidilutive stock options excluded from the computation of diluted earnings per share (in shares)			181,247	185,163