Goodwill and other intangible assets, net - Carrying Amount (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill
Goodwill, beginning balance	$ 12.4	$ 11.9
Foreign currency translation	0.0	0.5
Goodwill, ending balance	12.4	12.4
Performance Chemicals
Goodwill
Goodwill, beginning balance	8.1	7.6
Foreign currency translation	0.0	0.5
Goodwill, ending balance	8.1	8.1
Performance Materials
Goodwill
Goodwill, beginning balance	4.3	4.3
Foreign currency translation	0.0	0.0
Goodwill, ending balance	$ 4.3	$ 4.3