Segment and Related Information, Reportable Segments (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jul. 01, 2018 USD ($)	Jun. 30, 2019 USD ($) Segment	Jul. 01, 2018 USD ($)
Segment Reporting Information [Abstract]
Number of reportable segments | Segment			4
Net sales	$ 463.8	$ 464.7	$ 901.5	$ 896.0
Income from operations	45.5	62.8	107.5	125.4
Performance Materials [Member]
Segment Reporting Information [Abstract]
Net sales	215.4	214.5	414.6	401.8
Specialty Minerals [Member]
Segment Reporting Information [Abstract]
Net sales	145.1	150.9	289.5	300.5
Refractories [Member]
Segment Reporting Information [Abstract]
Net sales	77.5	79.6	151.3	154.9
Energy Services [Member]
Segment Reporting Information [Abstract]
Net sales	25.8	19.7	46.1	38.8
Reportable Segments [Member]
Segment Reporting Information [Abstract]
Net sales	463.8	464.7	901.5	896.0
Income from operations	48.7	65.7	111.5	130.3
Reportable Segments [Member] | Performance Materials [Member]
Segment Reporting Information [Abstract]
Net sales	215.4	214.5	414.6	401.8
Income from operations	20.7	29.6	47.0	55.8
Reportable Segments [Member] | Specialty Minerals [Member]
Segment Reporting Information [Abstract]
Net sales	145.1	150.9	289.5	300.5
Income from operations	20.0	25.1	42.0	49.2
Reportable Segments [Member] | Refractories [Member]
Segment Reporting Information [Abstract]
Net sales	77.5	79.6	151.3	154.9
Income from operations	7.1	10.3	19.2	23.1
Reportable Segments [Member] | Energy Services [Member]
Segment Reporting Information [Abstract]
Net sales	25.8	19.7	46.1	38.8
Income from operations	$ 0.9	$ 0.7	$ 3.3	$ 2.2