Segment and Related Information (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013 Segment	Dec. 31, 2012	Dec. 31, 2011
Segment and Related Information [Abstract]
Number of Reportable Segments									2
Segment Reporting Information [Line Items]
Net sales	$ 256,600,000	$ 254,200,000	$ 256,800,000	$ 250,400,000	$ 243,100,000	$ 247,800,000	$ 251,400,000	$ 254,500,000	$ 1,018,181,000	$ 996,764,000	$ 1,032,933,000
Income from operations									134,300,000	120,300,000	109,800,000
Restructuring and other charges									0	0	(411,000)
Depreciation, depletion and amortization									47,289,000	51,124,000	58,175,000
Segment assets	1,217,547,000				1,211,189,000				1,217,547,000	1,211,189,000	1,165,000,000
Capital expenditures									43,831,000	52,130,000	52,060,000
Goodwill	64,432,000				65,829,000				64,432,000	65,829,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments									134,300,000	120,300,000	109,800,000
Unallocated corporate expenses									(7,400,000)	(6,700,000)	(5,700,000)
Interest income									3,000,000	3,200,000	3,900,000
Interest expense									(3,263,000)	(3,221,000)	(3,254,000)
Other deductions									(2,800,000)	(3,000,000)	(3,200,000)
Income from continuing operations before provision for taxes									123,710,000	110,645,000	101,461,000
Specialty Minerals [Member]
Segment Reporting Information [Line Items]
Net sales	167,100,000	167,400,000	168,300,000	166,800,000	159,700,000	163,100,000	165,500,000	165,100,000	669,800,000	653,400,000	664,100,000
Income from operations									98,400,000	87,700,000	76,600,000
Restructuring and other charges											200,000
Depreciation, depletion and amortization									38,600,000	40,800,000	47,600,000
Segment assets	605,600,000				617,000,000				605,600,000	617,000,000	603,800,000
Capital expenditures									33,600,000	41,000,000	41,700,000
Goodwill	14,300,000				14,100,000				14,300,000	14,100,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments									98,400,000	87,700,000	76,600,000
Refractories [Member]
Segment Reporting Information [Line Items]
Net sales	89,500,000	86,800,000	88,500,000	83,600,000	83,400,000	84,700,000	85,900,000	89,400,000	348,400,000	343,400,000	368,800,000
Income from operations									35,900,000	32,600,000	33,200,000
Restructuring and other charges											(600,000)
Depreciation, depletion and amortization									8,700,000	10,300,000	10,600,000
Segment assets	378,100,000				355,500,000				378,100,000	355,500,000	355,800,000
Capital expenditures									8,300,000	8,000,000	8,000,000
Goodwill	50,100,000				51,700,000				50,100,000	51,700,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments									35,900,000	32,600,000	33,200,000
Total Segments [Member]
Segment Reporting Information [Line Items]
Segment assets	983,700,000				972,500,000				983,700,000	972,500,000	959,600,000
Capital expenditures									41,900,000	49,000,000	49,700,000
Corporate [Member]
Segment Reporting Information [Line Items]
Segment assets	233,800,000				238,700,000				233,800,000	238,700,000	205,400,000
Capital expenditures									$ 1,900,000	$ 3,100,000	$ 2,400,000