- Schedule of other intangible assets subject to amortization (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Aug. 31, 2018	Aug. 31, 2017	May 31, 2016	May 31, 2018
Finite-lived Intangible Assets [Roll Forward]
Beginning balance other intangibles subject to amortization	$ 10.1	$ 9.0
Additions	0.5	0.1	$ 3.3
Amortization expense	(0.7)	(0.5)	(2.1)
Foreign currency translation	0.0	0.0	$ (0.1)
Total other intangibles subject to amortization, net of accumulated amortization of $24.8, $24.1 and $22.5, respectively	9.9	8.6
Accumulated amortization of intangible assets	24.8	22.5		$ 24.1
Total other intangibles not subject to amortization	2.1	2.1		2.1
Total other intangibles	$ 12.0	$ 10.7		$ 12.2