Segment and Related Information, Reportable Segments (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Oct. 01, 2017 USD ($)	Sep. 30, 2018 USD ($) Segment	Oct. 01, 2017 USD ($)
Segment Reporting Information [Abstract]
Number of reportable segments | Segment			4
Net Sales	$ 464.1	$ 424.4	$ 1,360.1	$ 1,243.5
Income from Operations	68.2	67.2	193.6	198.3
Performance Materials [Member]
Segment Reporting Information [Abstract]
Net Sales	219.5	188.8	621.3	539.0
Specialty Minerals [Member]
Segment Reporting Information [Abstract]
Net Sales	146.3	147.7	446.8	440.9
Refractories [Member]
Segment Reporting Information [Abstract]
Net Sales	79.1	68.9	234.0	208.0
Energy Services [Member]
Segment Reporting Information [Abstract]
Net Sales	19.2	19.0	58.0	55.6
Reportable Segments [Member]
Segment Reporting Information [Abstract]
Net Sales	464.1	424.4	1,360.1	1,243.5
Income from Operations	69.4	69.4	199.7	203.9
Reportable Segments [Member] | Performance Materials [Member]
Segment Reporting Information [Abstract]
Net Sales	219.5	188.8	621.3	539.0
Income from Operations	31.8	30.6	87.6	91.6
Reportable Segments [Member] | Specialty Minerals [Member]
Segment Reporting Information [Abstract]
Net Sales	146.3	147.7	446.8	440.9
Income from Operations	25.0	26.6	74.2	77.9
Reportable Segments [Member] | Refractories [Member]
Segment Reporting Information [Abstract]
Net Sales	79.1	68.9	234.0	208.0
Income from Operations	11.5	9.9	34.6	29.6
Reportable Segments [Member] | Energy Services [Member]
Segment Reporting Information [Abstract]
Net Sales	19.2	19.0	58.0	55.6
Income from Operations	$ 1.1	$ 2.3	$ 3.3	$ 4.8