- Schedule of other intangible assets subject to amortization (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Aug. 31, 2017	Aug. 31, 2016	May 31, 2016	May 31, 2017
Finite-lived Intangible Assets [Roll Forward]
Beginning balance other intangibles subject to amortization	$ 9.0	$ 4.7
Additions	0.1	0.2	$ 7.0
Amortization expense	(0.5)	(0.6)	(2.5)
Foreign currency translation	0.0	(0.1)	(0.2)
Total other intangibles subject to amortization, net of accumulated amortization of $22.5, $22.0 and $20.1, respectively	8.6	4.2	$ 4.7
Accumulated amortization of intangible assets	22.5	20.1		$ 22.0
Total other intangibles not subject to amortization	2.1	2.1		2.1
Total other intangibles	$ 10.7	$ 6.3		$ 11.1