Segment and Related Information (Details) (USD $)	3 Months Ended		9 Months Ended
	Oct. 02, 2011	Oct. 03, 2010	Oct. 02, 2011	Oct. 03, 2010	Dec. 31, 2010
Segment Reporting Information [Line Items]
Net sales	$ 262,192,000	$ 249,812,000	$ 793,111,000	$ 759,039,000
Income from operations	26,800,000	26,000,000	79,400,000	78,800,000
Restructuring costs (reversals)	240,000	0	470,000	865,000
Goodwill	65,359,000		65,359,000		67,156,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	26,800,000	26,000,000	79,400,000	78,800,000
Unallocated corporate expenses	(1,400,000)	(1,000,000)	(4,200,000)	(3,300,000)
Income from operations	25,394,000	24,956,000	75,175,000	75,520,000
Non-operating deductions, net	(1,663,000)	(177,000)	(3,299,000)	309,000
Income from continuing operations before provision for taxes	23,731,000	24,779,000	71,876,000	75,829,000
Revenue from External Customer [Line Items]
Net sales	262,192,000	249,812,000	793,111,000	759,039,000
Specialty Minerals [Member]
Segment Reporting Information [Line Items]
Net sales	171,100,000	166,100,000	516,100,000	506,400,000
Income from operations	19,300,000	19,700,000	57,200,000	57,400,000
Restructuring costs (reversals)			400,000	500,000
Goodwill	13,900,000		13,900,000		13,800,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	19,300,000	19,700,000	57,200,000	57,400,000
Revenue from External Customer [Line Items]
Net sales	171,100,000	166,100,000	516,100,000	506,400,000
Refractories [Member]
Segment Reporting Information [Line Items]
Net sales	91,100,000	83,700,000	277,000,000	252,600,000
Income from operations	7,500,000	6,300,000	22,200,000	21,400,000
Restructuring costs (reversals)	200,000		0	400,000
Goodwill	51,500,000		51,500,000		53,300,000
Income from operations before provision for taxes on income [Abstract]
Income from operations for reportable segments	7,500,000	6,300,000	22,200,000	21,400,000
Revenue from External Customer [Line Items]
Net sales	91,100,000	83,700,000	277,000,000	252,600,000
Paper PCC [Member]
Segment Reporting Information [Line Items]
Net sales	126,500,000	121,700,000	379,300,000	375,600,000
Revenue from External Customer [Line Items]
Net sales	126,500,000	121,700,000	379,300,000	375,600,000
Specialty PCC [Member]
Segment Reporting Information [Line Items]
Net sales	16,000,000	15,400,000	48,200,000	44,100,000
Revenue from External Customer [Line Items]
Net sales	16,000,000	15,400,000	48,200,000	44,100,000
Talc [Member]
Segment Reporting Information [Line Items]
Net sales	11,300,000	12,500,000	35,400,000	34,100,000
Revenue from External Customer [Line Items]
Net sales	11,300,000	12,500,000	35,400,000	34,100,000
Ground Calcium Carbonate [Member]
Segment Reporting Information [Line Items]
Net sales	17,300,000	16,800,000	53,200,000	52,000,000
Revenue from External Customer [Line Items]
Net sales	17,300,000	16,800,000	53,200,000	52,000,000
Refractory Products [Member]
Segment Reporting Information [Line Items]
Net sales	71,100,000	65,400,000	216,100,000	196,200,000
Revenue from External Customer [Line Items]
Net sales	71,100,000	65,400,000	216,100,000	196,200,000
Metallurgical Products [Member]
Segment Reporting Information [Line Items]
Net sales	20,000,000	18,300,000	60,900,000	56,400,000
Revenue from External Customer [Line Items]
Net sales	$ 20,000,000	$ 18,300,000	$ 60,900,000	$ 56,400,000