Segment and Related Information (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 29, 2013	Sep. 30, 2012	Sep. 29, 2013	Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Net sales	$ 254,192,000	$ 247,803,000	$ 761,549,000	$ 753,719,000
Income from operations	34,400,000	30,500,000	98,200,000	91,900,000
Goodwill	64,683,000		64,683,000		65,829,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	34,400,000	30,500,000	98,200,000	91,900,000
Unallocated corporate expenses	(1,600,000)	(2,000,000)	(4,800,000)	(5,300,000)
Income from operations	32,757,000	28,565,000	93,388,000	86,594,000
Non-operating deductions, net	(1,234,000)	(650,000)	(2,572,000)	(2,016,000)
Income from continuing operations before provision for taxes	31,523,000	27,915,000	90,816,000	84,578,000
Specialty Minerals [Member]
Segment Reporting Information [Line Items]
Net sales	167,400,000	163,100,000	502,500,000	493,700,000
Income from operations	26,000,000	23,300,000	74,400,000	66,900,000
Goodwill	14,100,000		14,100,000		14,100,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	26,000,000	23,300,000	74,400,000	66,900,000
Refractories [Member]
Segment Reporting Information [Line Items]
Net sales	86,800,000	84,700,000	259,000,000	260,000,000
Income from operations	8,400,000	7,200,000	23,800,000	25,000,000
Goodwill	50,600,000		50,600,000		51,700,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	$ 8,400,000	$ 7,200,000	$ 23,800,000	$ 25,000,000