Segment and Related Information (Details) (USD $)	3 Months Ended		6 Months Ended
	Jul. 03, 2011	Jul. 04, 2010	Jul. 03, 2011	Jul. 04, 2010	Dec. 31, 2010
Segment Reporting Information [Line Items]
Net sales	$ 268,399,000	$ 255,770,000	$ 530,919,000	$ 509,227,000
Income from operations	26,400,000	28,600,000	52,600,000	52,800,000
Restructuring costs (reversals)	0	13,000	230,000	865,000
Goodwill	67,348,000		67,348,000		67,156,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	26,400,000	28,600,000	52,600,000	52,800,000
Unallocated corporate expenses	1,300,000	1,100,000	2,800,000	2,200,000
Income from operations	25,067,000	27,512,000	49,781,000	50,564,000
Non-operating deductions, net	(799,000)	535,000	(1,636,000)	486,000
Income from continuing operations before provision for taxes	24,268,000	28,047,000	48,145,000	51,050,000
Revenue from External Customer [Line Items]
Net sales	268,399,000	255,770,000	530,919,000	509,227,000
Specialty Minerals [Member]
Segment Reporting Information [Line Items]
Net sales	171,800,000	168,200,000	345,100,000	340,300,000
Income from operations	18,600,000	19,300,000	37,900,000	37,700,000
Restructuring costs (reversals)	400,000	(300,000)	400,000	500,000
Goodwill	14,200,000		14,200,000		13,800,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	18,600,000	19,300,000	37,900,000	37,700,000
Revenue from External Customer [Line Items]
Net sales	171,800,000	168,200,000	345,100,000	340,300,000
Refractories [Member]
Segment Reporting Information [Line Items]
Net sales	96,600,000	87,600,000	185,800,000	168,900,000
Income from operations	7,800,000	9,300,000	14,700,000	15,100,000
Restructuring costs (reversals)	200,000	300,000	200,000	400,000
Goodwill	53,100,000		53,100,000		53,300,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	7,800,000	9,300,000	14,700,000	15,100,000
Revenue from External Customer [Line Items]
Net sales	96,600,000	87,600,000	185,800,000	168,900,000
Paper PCC [Member]
Segment Reporting Information [Line Items]
Net sales	123,600,000	123,200,000	252,800,000	253,900,000
Revenue from External Customer [Line Items]
Net sales	123,600,000	123,200,000	252,800,000	253,900,000
Specialty PCC [Member]
Segment Reporting Information [Line Items]
Net sales	16,600,000	15,200,000	32,200,000	29,600,000
Revenue from External Customer [Line Items]
Net sales	16,600,000	15,200,000	32,200,000	29,600,000
Talc [Member]
Segment Reporting Information [Line Items]
Net sales	12,700,000	11,400,000	24,100,000	21,600,000
Revenue from External Customer [Line Items]
Net sales	12,700,000	11,400,000	24,100,000	21,600,000
Ground Calcium Carbonate [Member]
Segment Reporting Information [Line Items]
Net sales	18,900,000	18,400,000	36,000,000	35,200,000
Revenue from External Customer [Line Items]
Net sales	18,900,000	18,400,000	36,000,000	35,200,000
Refractory Products [Member]
Segment Reporting Information [Line Items]
Net sales	75,300,000	68,300,000	144,900,000	130,800,000
Revenue from External Customer [Line Items]
Net sales	75,300,000	68,300,000	144,900,000	130,800,000
Metallurgical Products [Member]
Segment Reporting Information [Line Items]
Net sales	21,300,000	19,300,000	40,900,000	38,100,000
Revenue from External Customer [Line Items]
Net sales	$ 21,300,000	$ 19,300,000	$ 40,900,000	$ 38,100,000