Segment and Related Information, Sales By Product Category (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 01, 2018	Jun. 30, 2019	Jul. 01, 2018
Revenue from External Customer [Abstract]
Net sales	$ 463.8	$ 464.7	$ 901.5	$ 896.0
Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	215.4	214.5	414.6	401.8
Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	145.1	150.9	289.5	300.5
Refractories [Member]
Revenue from External Customer [Abstract]
Net sales	77.5	79.6	151.3	154.9
Energy Services [Member]
Revenue from External Customer [Abstract]
Net sales	25.8	19.7	46.1	38.8
Metalcasting [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	75.8	88.8	149.0	168.0
Household, Personal Care and Specialty Products [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	69.0	58.6	143.9	107.3
Environmental Products [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	29.0	25.2	44.9	37.9
Building Materials [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	19.1	18.0	34.4	36.9
Basic Minerals [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	22.5	23.9	42.4	51.7
Paper PCC [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	90.2	94.5	181.7	191.5
Specialty PCC [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	17.3	17.3	35.4	34.3
Ground Calcium Carbonate [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	24.8	25.2	47.1	47.7
Talc [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	12.8	13.9	25.3	27.0
Refractory Products [Member] | Refractories [Member]
Revenue from External Customer [Abstract]
Net sales	61.0	66.7	123.0	129.0
Metallurgical Products [Member] | Refractories [Member]
Revenue from External Customer [Abstract]
Net sales	$ 16.5	$ 12.9	$ 28.3	$ 25.9