Segment and Related Information, Segment Information (Details) $ in Millions	3 Months Ended					12 Months Ended
	Apr. 04, 2021 USD ($) Segment	Dec. 31, 2020 USD ($)	Sep. 27, 2020 USD ($)	Jun. 28, 2020 USD ($)	Mar. 29, 2020 USD ($)	Dec. 31, 2020 USD ($)
Segment and Related Information [Abstract]
Number of reportable segments | Segment	3
Net sales	$ 452.6				$ 417.5
Income from operations	58.8				57.7
Performance Materials [Member]
Segment and Related Information [Abstract]
Net sales	230.9	$ 219.0	$ 203.9	$ 191.5	211.4	$ 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	147.8				137.1
Refractories [Member]
Segment and Related Information [Abstract]
Net sales	73.9				69.0
Reportable Segments [Member]
Segment and Related Information [Abstract]
Net sales	452.6				417.5
Income from operations	62.9				58.8
Reportable Segments [Member] | Performance Materials [Member]
Segment and Related Information [Abstract]
Net sales	230.9				211.4
Income from operations	29.8				27.3
Reportable Segments [Member] | Specialty Minerals [Member]
Segment and Related Information [Abstract]
Net sales	147.8				137.1
Income from operations	21.1				20.3
Reportable Segments [Member] | Refractories [Member]
Segment and Related Information [Abstract]
Net sales	73.9				69.0
Income from operations	$ 12.0				$ 11.2