Segment and Related Information, Segment Information (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 28, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 28, 2020 USD ($) Segment	Jun. 30, 2019 USD ($)
Segment Reporting Information [Abstract]
Number of reportable segments | Segment			4
Net sales	$ 357.2	$ 463.8	$ 774.7	$ 901.5
Income from operations	27.2	45.5	84.9	107.5
Performance Materials [Member]
Segment Reporting Information [Abstract]
Net sales	173.8	215.4	360.0	414.6
Specialty Minerals [Member]
Segment Reporting Information [Abstract]
Net sales	109.8	145.1	246.9	289.5
Refractories [Member]
Segment Reporting Information [Abstract]
Net sales	55.9	77.5	124.9	151.3
Energy Services [Member]
Segment Reporting Information [Abstract]
Net sales	17.7	25.8	42.9	46.1
Reportable Segments [Member]
Segment Reporting Information [Abstract]
Net sales	357.2	463.8	774.7	901.5
Income from operations	37.3	48.7	96.1	111.5
Reportable Segments [Member] | Performance Materials [Member]
Segment Reporting Information [Abstract]
Net sales	173.8	215.4	360.0	414.6
Income from operations	21.0	20.7	45.1	47.0
Reportable Segments [Member] | Specialty Minerals [Member]
Segment Reporting Information [Abstract]
Net sales	109.8	145.1	246.9	289.5
Income from operations	9.0	20.0	29.3	42.0
Reportable Segments [Member] | Refractories [Member]
Segment Reporting Information [Abstract]
Net sales	55.9	77.5	124.9	151.3
Income from operations	5.9	7.1	17.1	19.2
Reportable Segments [Member] | Energy Services [Member]
Segment Reporting Information [Abstract]
Net sales	17.7	25.8	42.9	46.1
Income from operations	$ 1.4	$ 0.9	$ 4.6	$ 3.3