Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Nov. 30, 2019	Nov. 30, 2018	Nov. 30, 2019	Nov. 30, 2018
Earnings per Share
Effect, participating securities			$ 0.0
Basic and Diluted EPS:
Income from continuing operations	$ 20.1	$ 11.2	37.2	$ 30.1
Less income attributable to participating shares	(0.1)	(0.1)	(0.2)	(0.1)
Income from continuing operations attributable to common shareholders	20.0	11.1	37.0	30.0
Loss from discontinued operations attributable to common shareholders	(5.9)	(4.2)	(18.6)	(8.0)
Net income attributable to common shareholders for earnings per share	$ 14.1	$ 6.9	$ 18.4	$ 22.0
Weighted Average Shares:
Weighted average common shares outstanding - basic	34,600,000	34,600,000	34,600,000	34,600,000
Additional shares from the assumed exercise of stock options	400,000	400,000	400,000	500,000
Weighted average common shares outstanding - diluted	35,000,000.0	35,000,000.0	35,000,000.0	35,100,000
Earnings per share - basic:
Earnings from continuing operations	$ 0.58	$ 0.32	$ 1.07	$ 0.87
Loss from discontinued operations	(0.17)	(0.12)	(0.54)	(0.23)
Earnings per share - basic	0.41	0.20	0.53	0.64
Earnings per share - diluted:
Earnings from continuing operations	0.57	0.32	1.06	0.85
Loss from discontinued operations	(0.17)	(0.12)	(0.53)	(0.23)
Earnings per share - diluted	$ 0.40	$ 0.20	$ 0.53	$ 0.62
Antidilutive shares excluded from the computation of diluted earnings per share (in shares)	267,000	290,000	267,000	290,000