Segment and Related Information, Sales By Product Category (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 27, 2020	Sep. 29, 2019	Sep. 27, 2020	Sep. 29, 2019
Revenue from External Customer [Abstract]
Net sales	$ 388.3	$ 449.3	$ 1,163.0	$ 1,350.8
Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	190.6	207.3	550.6	621.9
Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	125.1	143.1	372.0	432.6
Refractories [Member]
Revenue from External Customer [Abstract]
Net sales	59.3	73.4	184.2	224.7
Energy Services [Member]
Revenue from External Customer [Abstract]
Net sales	13.3	25.5	56.2	71.6
Metalcasting [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	66.3	69.0	180.8	218.0
Household, Personal Care & Specialty Products [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	93.9	94.1	278.0	280.4
Environmental Products [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	16.9	27.1	48.3	72.0
Building Materials [Member] | Performance Materials [Member]
Revenue from External Customer [Abstract]
Net sales	13.5	17.1	43.5	51.5
Paper PCC [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	74.5	90.2	225.1	271.9
Specialty PCC [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	17.3	17.7	49.7	53.1
Ground Calcium Carbonate [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	23.2	23.0	66.4	70.1
Talc [Member] | Specialty Minerals [Member]
Revenue from External Customer [Abstract]
Net sales	10.1	12.2	30.8	37.5
Refractory Products [Member] | Refractories [Member]
Revenue from External Customer [Abstract]
Net sales	48.8	61.3	151.7	184.3
Metallurgical Products [Member] | Refractories [Member]
Revenue from External Customer [Abstract]
Net sales	$ 10.5	$ 12.1	$ 32.5	$ 40.4