Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	May 31, 2017	Feb. 28, 2017	Nov. 30, 2016	Aug. 31, 2016	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	Aug. 31, 2015	May 31, 2017	May 31, 2016	May 31, 2015
Earnings Per Share
Effect to the participating securities as result of net loss									$ 0.0
Basic and Diluted EPS:
Income (Loss) from continuing operations	$ 15.1	$ 13.1	$ 12.1	$ 9.9	$ 11.8	$ 9.9	$ 9.2	$ 7.4	50.2	$ 38.3	$ (73.9)
Less income attributable to participating shares									(0.5)	(0.4)	(0.3)
Income (Loss) from continuing operations attributable to common shareholders									49.7	37.9	(74.2)
Income from discontinued operations attributable to common shareholders	$ 6.1	$ 0.6		$ (0.4)	$ 0.2	$ (5.1)	$ (1.2)	$ 15.5	6.3	9.4	84.1
Net income attributable to common shareholders for earnings per share									$ 56.0	$ 47.3	$ 9.9
Weighted Average Shares:
Weighted average common shares outstanding - basic									33,900,000	34,400,000	39,100,000
Additional shares from assumed exercise of stock options									400,000	200,000	300,000
Weighted average common shares outstanding - diluted									34,300,000	34,600,000	39,400,000
Earnings per share - basic:
Earnings (Loss) from continuing operations	$ 0.44	$ 0.39	$ 0.35	$ 0.29	$ 0.35	$ 0.29	$ 0.26	$ 0.21	$ 1.47	$ 1.10	$ (1.90)
Earnings from discontinued operations	0.18	0.02		(0.01)		(0.15)	(0.03)	0.44	0.19	0.27	2.16
Earnings per share - basic	0.62	0.41	0.35	0.28	0.35	0.14	0.23	0.65	1.66	1.37	0.26
Earnings per share - diluted:
Earnings (Loss) from continuing operations	0.44	0.38	0.35	0.29	0.34	0.29	0.26	0.21	1.45	1.10	(1.90)
Earnings from discontinued operations	0.18	0.02		(0.01)		(0.15)	(0.03)	0.44	0.19	0.27	2.14
Earnings per share - diluted	$ 0.62	$ 0.40	$ 0.35	$ 0.28	$ 0.34	$ 0.14	$ 0.23	$ 0.65	$ 1.64	$ 1.37	$ 0.24
Antidilutive stock options excluded from the computation of diluted earnings per share (in shares)									11,200	1,374,200	168,200