Segment and Related Information, Sales By Product Category (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 29, 2019	Sep. 30, 2018	Sep. 29, 2019	Sep. 30, 2018
Revenue from External Customer [Abstract]
Net sales	$ 449.3	$ 464.1	$ 1,350.8	$ 1,360.1
Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	207.3	219.5	621.9	621.3
Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	143.1	146.3	432.6	446.8
Refractories [Member]
Revenue from External Customer [Abstract]
Net sales	73.4	79.1	224.7	234.0
Energy Services [Member]
Revenue from External Customer [Abstract]
Net sales	25.5	19.2	71.6	58.0
Metalcasting [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	69.0	77.8	218.0	245.8
Household, Personal Care and Specialty Products [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	94.1	97.4	280.4	256.4
Environmental Products [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	27.1	26.3	72.0	64.2
Building Materials [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	17.1	18.0	51.5	54.9
Paper PCC [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	90.2	93.1	271.9	284.6
Specialty PCC [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	17.7	16.9	53.1	51.2
Ground Calcium Carbonate [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	23.0	23.0	70.1	70.7
Talc [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	12.2	13.3	37.5	40.3
Refractory Products [Member] | Refractories [Member]
Revenue from External Customer [Abstract]
Net sales	61.3	66.7	184.3	195.7
Metallurgical Products [Member] | Refractories [Member]
Revenue from External Customer [Abstract]
Net sales	$ 12.1	$ 12.4	$ 40.4	$ 38.3