Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Feb. 28, 2021	Feb. 29, 2020	Feb. 28, 2021	Feb. 29, 2020
Earnings per Share
Effect, participating securities			$ 0.0
Basic and Diluted EPS:
Income from continuing operations	$ 31.1	$ 2.6	31.6	$ 39.8
Less income attributable to participating shares	(0.2)		(0.2)	(0.2)
Income from continuing operations attributable to common stockholders	30.9	2.6	31.4	39.6
Loss from discontinued operations attributable to common stockholders	(3.0)	(0.3)	(9.8)	(18.9)
Net income (loss) attributable to common stockholders for earnings per share	$ 27.9	$ 2.3	$ 21.6	$ 20.7
Weighted Average Shares:
Weighted average common shares outstanding - basic	35,000,000.0	34,700,000	35,000,000.0	34,800,000
Additional shares from the assumed exercise of stock options	500,000	400,000	200,000	300,000
Weighted average common shares outstanding - diluted	35,500,000	35,100,000	35,200,000	35,100,000
Earnings per share - basic:
Earnings from continuing operations	$ 0.88	$ 0.08	$ 0.90	$ 1.14
Loss from discontinued operations	(0.09)	(0.01)	(0.28)	(0.54)
Earnings per share - basic	0.79	0.07	0.62	0.60
Earnings (Loss) per share - diluted:
Earnings from continuing operations	0.87	0.07	0.89	1.13
Loss from discontinued operations	(0.08)	(0.01)	(0.28)	(0.54)
Earnings per share - diluted	$ 0.79	$ 0.06	$ 0.61	$ 0.59
Antidilutive shares excluded from the computation of diluted earnings per share (in shares)	653,000	265,000	1,187,000	265,000