Segment and Related Information, Segment Information (Details) $ in Millions	3 Months Ended					6 Months Ended		12 Months Ended
	Jul. 04, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 27, 2020 USD ($)	Jun. 28, 2020 USD ($)	Mar. 29, 2020 USD ($)	Jul. 04, 2021 USD ($) Segment	Jun. 28, 2020 USD ($)	Dec. 31, 2020 USD ($)
Segment and Related Information [Abstract]
Number of reportable segments | Segment						3
Net sales	$ 455.6			$ 357.2		$ 908.2	$ 774.7
Income from operations	63.7			27.2		122.5	84.9
Performance Materials [Member]
Segment and Related Information [Abstract]
Net sales	238.4	$ 219.0	$ 203.9	191.5	$ 211.4	469.3	402.9	$ 825.8
Income from operations		$ 30.9	$ 28.2	22.4	$ 27.3			$ 108.8
Specialty Minerals [Member]
Segment and Related Information [Abstract]
Net sales	142.7			109.8		290.5	246.9
Refractories [Member]
Segment and Related Information [Abstract]
Net sales	74.5			55.9		148.4	124.9
Reportable Segments [Member]
Segment and Related Information [Abstract]
Net sales	455.6			357.2		908.2	774.7
Income from operations	66.4			37.3		129.3	96.1
Reportable Segments [Member] | Performance Materials [Member]
Segment and Related Information [Abstract]
Net sales	238.4			191.5		469.3	402.9
Income from operations	34.7			22.4		64.5	49.7
Reportable Segments [Member] | Specialty Minerals [Member]
Segment and Related Information [Abstract]
Net sales	142.7			109.8		290.5	246.9
Income from operations	20.0			9.0		41.1	29.3
Reportable Segments [Member] | Refractories [Member]
Segment and Related Information [Abstract]
Net sales	74.5			55.9		148.4	124.9
Income from operations	$ 11.7			$ 5.9		$ 23.7	$ 17.1