Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	May 31, 2020	Feb. 29, 2020	Nov. 30, 2019	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2020	May 31, 2019	May 31, 2018
Earnings Per Share
Effect to the participating securities as result of net loss									$ 0.0
Basic and Diluted EPS:
Income (Loss) from continuing operations	$ (15.0)	$ 2.6	$ 20.1	$ 17.1	$ 26.6	$ 27.4	$ 11.2	$ 18.9	24.8	$ 84.1	$ 73.7
Less income attributable to participating shares									(0.1)	(0.4)	(0.6)
Income from continuing operations attributable to common stockholders									24.7	83.7	73.1
Loss from discontinued operations attributable to common stockholders									(20.4)	(76.6)	(58.1)
Net income attributable to common stockholders for earnings per share									$ 4.3	$ 7.1	$ 15.0
Weighted Average Shares:
Weighted average common shares outstanding - basic									34,800,000	34,500,000	34,200,000
Additional shares from the assumed exercise of stock options									200,000	400,000	400,000
Weighted average common shares outstanding - diluted									35,000,000.0	34,900,000	34,600,000
Earnings per share - basic:
Earnings from continuing operations	$ (0.43)	$ 0.08	$ 0.58	$ 0.49	$ 0.77	$ 0.79	$ 0.32	$ 0.54	$ 0.71	$ 2.42	$ 2.14
Loss from discontinued operations	(0.04)	(0.01)	(0.17)	(0.37)	(0.11)	(1.87)	(0.12)	(0.11)	(0.59)	(2.22)	(1.70)
Earnings per share - basic	(0.47)	0.07	0.41	0.12	0.66	(1.08)	0.20	0.43	0.12	0.20	0.44
Earnings per share - diluted:
Earnings from continuing operations	(0.43)	0.07	0.57	0.49	0.76	0.78	0.32	0.54	0.71	2.40	2.11
Loss from discontinued operations	(0.04)	(0.01)	(0.17)	(0.36)	(0.11)	(1.86)	(0.12)	(0.11)	(0.58)	(2.19)	(1.70)
Earnings per share - diluted	$ (0.47)	$ 0.06	$ 0.40	$ 0.13	$ 0.65	$ (1.08)	$ 0.20	$ 0.43	$ 0.13	$ 0.21	$ 0.41
Antidilutive shares excluded from the computation of diluted earnings per share (in shares)									669,400	273,400