Segment and Related Information, Segment Information (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 27, 2020 USD ($)	Jun. 28, 2020 USD ($)	Mar. 29, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 29, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment and Related Information [Abstract]
Number of reportable segments | Segment									4
Segment Reporting Information [Abstract]
Net sales	$ 431.8	$ 388.3	$ 357.2	$ 417.5	$ 440.2	$ 449.3	$ 463.8	$ 437.7	$ 1,594.8	$ 1,791.0	$ 1,807.6
Income from operations	54.5	48.5	27.2	57.7	47.7	53.5	45.5	62.0	187.9	208.7	255.9
Depreciation, depletion and amortization									93.9	98.4	94.3
Segment assets	3,209.4				3,112.6				3,209.4	3,112.6	3,087.1
Capital expenditures									66.8	65.0	75.9
Income from Operations before Tax and Equity in Earnings [Abstract]
Litigation expenses									(10.4)	(10.9)	0.0
Acquisition-related expenses									(3.1)	0.0	(1.7)
Unallocated corporate expenses									(10.7)	(8.2)	(4.5)
Consolidated income from operations	54.5	48.5	27.2	57.7	47.7	53.5	45.5	62.0	187.9	208.7	255.9
Non-operating deductions, net									(49.9)	(51.4)	(51.8)
Income from operations before provision for taxes and equity in earnings									138.0	157.3	204.1
Performance Materials [Member]
Segment Reporting Information [Abstract]
Net sales	202.2	190.6	173.8	186.2	201.4	207.3	215.4	199.2	752.8	823.3	828.1
Specialty Minerals [Member]
Segment Reporting Information [Abstract]
Net sales	138.9	125.1	109.8	137.1	141.8	143.1	145.1	144.4	510.9	574.4	589.3
Refractories [Member]
Segment Reporting Information [Abstract]
Net sales	73.9	59.3	55.9	69.0	73.4	73.4	77.5	73.8	258.1	298.1	311.9
Energy Services [Member]
Segment Reporting Information [Abstract]
Net sales	16.8	$ 13.3	$ 17.7	$ 25.2	23.6	$ 25.5	$ 25.8	$ 20.3	73.0	95.2	78.3
Reportable Segments [Member]
Segment Reporting Information [Abstract]
Net sales									1,594.8	1,791.0	1,807.6
Income from operations									212.1	227.8	262.1
Depreciation, depletion and amortization									93.9	98.4	94.3
Segment assets	3,069.5				3,031.0				3,069.5	3,031.0	3,038.6
Capital expenditures									66.6	64.9	74.7
Income from Operations before Tax and Equity in Earnings [Abstract]
Consolidated income from operations									212.1	227.8	262.1
Reportable Segments [Member] | Performance Materials [Member]
Segment Reporting Information [Abstract]
Net sales									752.8	823.3	828.1
Income from operations									103.6	97.1	116.8
Depreciation, depletion and amortization									41.4	43.6	41.1
Segment assets	2,111.6				2,091.2				2,111.6	2,091.2	2,119.7
Capital expenditures									10.0	16.8	22.4
Income from Operations before Tax and Equity in Earnings [Abstract]
Consolidated income from operations									103.6	97.1	116.8
Reportable Segments [Member] | Specialty Minerals [Member]
Segment Reporting Information [Abstract]
Net sales									510.9	574.4	589.3
Income from operations									67.8	83.1	95.4
Depreciation, depletion and amortization									39.6	40.4	38.2
Segment assets	559.6				525.1				559.6	525.1	511.9
Capital expenditures									46.5	37.7	42.4
Income from Operations before Tax and Equity in Earnings [Abstract]
Consolidated income from operations									67.8	83.1	95.4
Reportable Segments [Member] | Refractories [Member]
Segment Reporting Information [Abstract]
Net sales									258.1	298.1	311.9
Income from operations									35.5	39.8	45.4
Depreciation, depletion and amortization									6.9	7.0	6.6
Segment assets	290.8				293.2				290.8	293.2	296.6
Capital expenditures									5.5	5.7	5.0
Income from Operations before Tax and Equity in Earnings [Abstract]
Consolidated income from operations									35.5	39.8	45.4
Reportable Segments [Member] | Energy Services [Member]
Segment Reporting Information [Abstract]
Net sales									73.0	95.2	78.3
Income from operations									5.2	7.8	4.5
Depreciation, depletion and amortization									6.0	7.4	8.4
Segment assets	107.5				121.5				107.5	121.5	110.4
Capital expenditures									4.6	4.7	4.9
Income from Operations before Tax and Equity in Earnings [Abstract]
Consolidated income from operations									5.2	7.8	4.5
Unallocated and Other Corporate Expenses [Member]
Segment Reporting Information [Abstract]
Segment assets	$ 139.9				$ 81.6				139.9	81.6	48.5
Capital expenditures									$ 0.2	$ 0.1	$ 1.2