Segment and Related Information (Details) (USD $)	3 Months Ended
	Mar. 30, 2014		Mar. 31, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net sales	$ 244,396,000		$ 250,513,000
Income from operations	30,700,000		30,200,000
Goodwill	64,274,000	[1]		64,432,000	[2]
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	30,700,000		30,200,000
Unallocated corporate expenses	(7,100,000)		(2,000,000)
Consolidated income from operations	23,584,000		28,253,000
Non-operating income (deductions), net	(310,000)		133,000
Income from continuing operations before provision for taxes	23,274,000		28,386,000
Specialty Minerals [Member]
Segment Reporting Information [Line Items]
Net sales	159,700,000		166,900,000
Income from operations	21,500,000		23,300,000
Goodwill	14,400,000			14,300,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	21,500,000		23,300,000
Refractories [Member]
Segment Reporting Information [Line Items]
Net sales	84,700,000		83,600,000
Income from operations	9,200,000		6,900,000
Goodwill	49,900,000			50,100,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	$ 9,200,000		$ 6,900,000

[1] Unaudited

[2] Condensed from audited financial statements