Earnings per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Aug. 31, 2021	Aug. 31, 2020
Earnings per Share
Effect, participating securities	$ 0.0
Basic and Diluted EPS:
Income (Loss) from continuing operations	11.2	$ (13.9)
Less income attributable to participating shares	(0.1)	0.0
Income (Loss) from continuing operations attributable to common shareholders	11.1	(13.9)
Income (Loss) from discontinued operations attributable to common shareholders	0.3	(0.6)
Net income (loss) attributable to common stockholders for earnings per share	$ 11.4	$ (14.5)
Weighted Average Shares:
Weighted average common shares outstanding - basic	35,100,000	34,900,000
Additional shares from assumed exercise of stock options	600,000	100,000
Weighted average common shares outstanding - diluted	35,700,000	35,000,000.0
Earnings (Loss) per share - basic:
Earnings (Loss) from continuing operations	$ 0.32	$ (0.40)
Earnings (Loss) from discontinued operations	0.01	(0.02)
Earnings (Loss) per share - basic	0.33	(0.42)
Earnings (Loss) per share - diluted:
Earnings (Loss) from continuing operations	0.31	(0.40)
Earnings (Loss) from discontinued operations	0.01	(0.02)
Earnings (Loss) per share - diluted	$ 0.32	$ (0.42)
Antidilutive shares excluded from the computation of diluted earnings per share (in shares)	793,000	1,750,000