Segment and Related Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Oct. 02, 2011	Jul. 03, 2011	Apr. 03, 2011	Dec. 31, 2010	Oct. 03, 2010	Jul. 04, 2010	Apr. 04, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting Information [Line Items]
Net sales	$ 251,700	$ 262,200	$ 268,400	$ 262,500	$ 243,300	$ 249,800	$ 255,800	$ 253,500	$ 1,044,853	$ 1,002,354	$ 907,321
Income (loss) from operations									97,740	98,849	(23,140)
Impairment of assets									0	0	39,831
Restructuring and other charges									470	865	22,024
Depreciation, depletion and amortization									58,223	63,981	72,401
Segment assets	1,164,955				1,116,105				1,164,955	1,116,105	1,072,100
Capital expenditures									52,060	34,518	26,591
Specialty Minerals [Member]
Segment Reporting Information [Line Items]
Net sales	159,900	171,100	171,800	173,300	158,600	166,100	168,200	172,100	676,100	665,000	628,400
Income (loss) from operations									72,800	74,700	34,200
Impairment of assets											8,500
Restructuring and other charges									1,000	500	11,500
Depreciation, depletion and amortization									47,600	52,600	58,500
Segment assets	603,800				585,700				603,800	585,700	631,700
Capital expenditures									41,700	23,300	19,100
Refractories [Member]
Segment Reporting Information [Line Items]
Net sales	91,800	91,100	96,600	89,200	84,700	83,700	87,600	81,400	368,800	337,400	278,900
Income (loss) from operations									33,200	28,000	(48,800)
Impairment of assets											31,300
Restructuring and other charges									(600)	300	10,500
Depreciation, depletion and amortization									10,600	11,400	13,900
Segment assets	355,800				340,500				355,800	340,500	326,200
Capital expenditures									8,000	8,200	5,600
Total Segments [Member]
Segment Reporting Information [Line Items]
Income (loss) from operations									106,000	102,700	(14,600)
Impairment of assets											39,800
Segment assets	959,600				926,200				959,600	926,200	957,900
Capital expenditures									$ 49,700	$ 31,500	$ 24,700