Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	May 31, 2016	Feb. 29, 2016	Nov. 30, 2015	Aug. 31, 2015	May 31, 2015	Feb. 28, 2015	Nov. 30, 2014	Aug. 31, 2014	May 31, 2016	May 31, 2015	May 31, 2014
Earnings Per Share
Effect to the participating securities as result of net loss									$ 0.0
Basic EPS:
Income (Loss) from continuing operations	$ 11.2	$ 10.7	$ 10.4	$ 8.2	$ (82.1)	$ 1.9	$ 13.9	$ 11.8	40.5	$ (54.5)	$ 67.2
Less income attributable to participating shares									(0.5)	(0.3)	(1.5)
Income (Loss) from continuing operations attributable to common shareholders									40.0	(54.8)	65.7
Income from discontinued operations attributable to common shareholders	0.8	(5.9)	(2.4)	14.7	97.2	(36.4)	1.3	2.6	7.2	64.7	5.7
Net income attributable to common shareholders for earnings per share - basic									47.2	9.9	71.4
Diluted EPS:
Income (Loss) from continuing operations	11.2	10.7	10.4	8.2	(82.1)	1.9	13.9	11.8	40.5	(54.5)	67.2
Less income attributable to participating shares									(0.5)	(0.3)	(1.5)
Income (Loss) from continuing operations attributable to common shareholders									40.0	(54.8)	65.7
Income from discontinued operations attributable to common shareholders	$ 0.8	$ (5.9)	$ (2.4)	$ 14.7	$ 97.2	$ (36.4)	$ 1.3	$ 2.6	7.2	64.7	5.7
Net income attributable to common shareholders for earnings per share - diluted									$ 47.2	$ 9.9	$ 71.4
Weighted average common shares outstanding - basic									34,400,000	39,100,000	38,600,000
Additional shares from the assumed exercise of stock options									200,000	300,000	500,000
Weighted average common shares outstanding - diluted									34,600,000	39,400,000	39,100,000
Earnings per share - basic:
Earnings (Loss) from continuing operations	$ 0.32	$ 0.31	$ 0.30	$ 0.23	$ (2.12)	$ 0.05	$ 0.35	$ 0.29	$ 1.16	$ (1.40)	$ 1.70
Earnings from discontinued operations	0.03	(0.17)	(0.07)	0.42	2.50	(0.94)	0.03	0.07	0.21	1.66	0.15
Earnings per share - basic	0.35	0.14	0.23	0.65	0.38	(0.89)	0.38	0.36	1.37	0.26	1.85
Earnings per share - diluted:
Earnings (Loss) from continuing operations	0.32	0.31	0.30	0.23	(2.12)	0.05	0.35	0.29	1.16	(1.40)	1.68
Earnings from discontinued operations	0.02	(0.17)	(0.07)	0.42	2.48	(0.94)	0.03	0.07	0.21	1.64	0.15
Earnings per share - diluted	$ 0.34	$ 0.14	$ 0.23	$ 0.65	$ 0.36	$ (0.89)	$ 0.38	$ 0.36	$ 1.37	$ 0.24	$ 1.83
Antidilutive stock options excluded from the computation of diluted earnings per share (in shares)									1,374,200	168,200	180,000