Segment and Related Information (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jul. 01, 2012	Jun. 30, 2013	Jul. 01, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Net sales	$ 256,844,000	$ 251,358,000	$ 507,357,000	$ 505,916,000
Income from operations	33,700,000	31,400,000	63,900,000	61,300,000
Goodwill	64,592,000		64,592,000		65,829,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	33,700,000	31,400,000	63,900,000	61,300,000
Unallocated corporate expenses	(1,300,000)	(1,300,000)	(3,300,000)	(3,300,000)
Income from operations	32,379,000	30,140,000	60,632,000	58,029,000
Non-operating deductions, net	(1,472,000)	(767,000)	(1,339,000)	(1,366,000)
Income from continuing operations before provision for taxes	30,907,000	29,373,000	59,293,000	56,663,000
Specialty Minerals [Member]
Segment Reporting Information [Line Items]
Net sales	168,300,000	165,500,000	335,300,000	330,600,000
Income from operations	25,200,000	22,700,000	48,500,000	43,500,000
Goodwill	13,700,000		13,700,000		14,100,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	25,200,000	22,700,000	48,500,000	43,500,000
Refractories [Member]
Segment Reporting Information [Line Items]
Net sales	88,500,000	85,900,000	172,100,000	175,300,000
Income from operations	8,500,000	8,700,000	15,400,000	17,800,000
Goodwill	50,900,000		50,900,000		51,700,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	$ 8,500,000	$ 8,700,000	$ 15,400,000	$ 17,800,000