Restructuring Expenses and Repositioning Expenses - Expenses and Asset Impairments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 1.0	$ 2.0	$ 2.0	$ 4.8
Catalysts Technologies
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	1.0	0.0	1.5	0.4
Materials Technologies
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	0.0	0.1	0.4	0.3
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 0.0	$ 1.9	$ 0.1	$ 4.1