Restructuring Expenses and Repositioning Expenses - Expenses and Asset Impairments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 1.9	$ 1.0	$ 3.0	$ 2.0
Catalysts Technologies
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	1.9	1.0	2.1	1.5
Materials Technologies
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	0.2	0.0	1.2	0.4
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ (0.2)	$ 0.0	$ (0.3)	$ 0.1