Goodwill and Other Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Roll Forward]
Balance Beginning	$ 778.7	$ 781.2
Change in goodwill relating to [Abstract]
Foreign exchange translation	0.6	(2.5)
Total	0.6	(2.5)
Balance Ending	$ 779.3	778.7
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	28 years
Gross carrying amount	$ 229.5	229.5
Accumulated amortization	33.0	25.1
Specialty Minerals [Member]
Goodwill [Roll Forward]
Balance Beginning	12.1	13.3
Change in goodwill relating to [Abstract]
Foreign exchange translation	0.6	(1.2)
Total	0.6	(1.2)
Balance Ending	12.7	12.1
Refractories [Member]
Goodwill [Roll Forward]
Balance Beginning	45.7	47.0
Change in goodwill relating to [Abstract]
Foreign exchange translation	0.0	(1.3)
Total	0.0	(1.3)
Balance Ending	45.7	45.7
Performance Materials [Member]
Goodwill [Roll Forward]
Balance Beginning	720.9	720.9
Change in goodwill relating to [Abstract]
Foreign exchange translation	0.0	0.0
Total	0.0	0.0
Balance Ending	$ 720.9	720.9
Trade Names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	34 years
Gross carrying amount	$ 199.8	199.8
Accumulated amortization	$ 20.7	15.3
Technology [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	12 years
Gross carrying amount	$ 18.8	18.8
Accumulated amortization	$ 4.8	3.6
Patents and Trademarks [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	17 years
Gross carrying amount	$ 6.4	6.4
Accumulated amortization	$ 5.3	4.8
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted average useful life	30 years
Gross carrying amount	$ 4.5	4.5
Accumulated amortization	$ 2.2	$ 1.4