Restructuring and Other Items, net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring, settlement and impairment provisions [Abstract]
Annualized savings from reduction of workforce	$ 12.0
Restructuring Charges [Abstract]
Impairment of assets	7.5	$ 0.7	$ 5.3
Severance and other employee costs	5.7	1.8	10.8
Total restructuring and other items, net	13.2	2.5	15.0
Restructuring Reserve [Roll Forward]
Restructuring liability, beginning of period	2.5
Additional provisions	5.7
Cash payments	(3.2)
Other	0.0
Restructuring liability, ending of period	5.0	2.5
Performance Materials [Member]
Restructuring Charges [Abstract]
Impairment of assets	4.2	0.0	0.0
Severance and other employee costs	2.8	0.0	0.0
Specialty Minerals [Member]
Restructuring Charges [Abstract]
Impairment of assets	1.6	0.7	5.3
Severance and other employee costs	0.9	0.0	5.0
Refractories [Member]
Restructuring Charges [Abstract]
Severance and other employee costs	0.8	0.0	0.0
Energy Services [Member]
Restructuring Charges [Abstract]
Impairment of assets	1.7	0.0	0.0
Severance and other employee costs	0.1	1.8	1.7
Other	0.0	0.0	(1.1)
Corporate [Member]
Restructuring Charges [Abstract]
Severance and other employee costs	$ 1.1	$ 0.0	$ 4.1