Commitments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended			1 Months Ended		1 Months Ended		12 Months Ended			1 Months Ended		12 Months Ended												12 Months Ended				12 Months Ended		1 Months Ended	12 Months Ended				12 Months Ended	1 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Nov. 01, 2008 Lease Agreements	Dec. 31, 2011 Lease Agreements	Nov. 01, 2008 Prior Agreement Lease Agreements	Oct. 31, 2008 Bauxite raw materials Supplier 4	Dec. 31, 2011 Bauxite raw materials Supplier 4	Dec. 31, 2010 Bauxite raw materials Supplier 4	Dec. 31, 2009 Bauxite raw materials Supplier 4	Oct. 31, 2008 Bauxite raw materials Supplier 4 Within Three Years From Agreement Date ton	Oct. 31, 2008 Bauxite raw materials Supplier 4 More Than Three Years From Agreement Date ton	Dec. 31, 2011 During 2012 Natural Gas Purchase Contract	Dec. 31, 2011 During 2013 Natural Gas Purchase Contract	Dec. 31, 2011 During 2014 Natural Gas Purchase Contract	Dec. 31, 2011 During 2015 Natural Gas Purchase Contract	Dec. 31, 2011 During 2016 Natural Gas Purchase Contract	Dec. 31, 2010 CHINA Bauxite And Hard Clays Supplier 5	Dec. 31, 2002 CHINA Bauxite And Hard Clays Supplier 5	Dec. 31, 2011 CHINA Bauxite And Hard Clays Supplier 6	Dec. 31, 2010 CHINA Bauxite And Hard Clays Supplier 6	Dec. 31, 2009 CHINA Bauxite And Hard Clays Supplier 6	Dec. 31, 2002 CHINA Bauxite And Hard Clays Supplier 6	Dec. 31, 2002 CHINA Bauxite And Hard Clays Supplier 6 Minimum	Dec. 31, 2010 Eufaula kaolin Supplier 1	Dec. 31, 2009 Eufaula kaolin Supplier 1	Dec. 31, 2003 Eufaula kaolin Supplier 1	Dec. 31, 2003 Eufaula kaolin Supplier 1 Minimum	Dec. 31, 2011 Eufaula kaolin Supplier 2	Dec. 31, 2011 Eufaula kaolin Supplier 2 Minimum	Jan. 31, 2003 McIntyre kaolin Supplier 3	Dec. 31, 2011 McIntyre kaolin Supplier 3	Dec. 31, 2010 McIntyre kaolin Supplier 3	Dec. 31, 2009 McIntyre kaolin Supplier 3	Jan. 31, 2003 McIntyre kaolin Supplier 3 Minimum	Dec. 31, 2011 Marshfield, Wisconsin	Jan. 30, 2012 Marshfield, Wisconsin After Amendment	Jul. 31, 2011 Marshfield, Wisconsin Prior Agreement	Jul. 31, 2011 Marshfield, Wisconsin During 2011 Prior Agreement ton	Jan. 30, 2012 Marshfield, Wisconsin During 2012 After Amendment ton	Jul. 31, 2011 Marshfield, Wisconsin During 2012 Prior Agreement ton	Jan. 30, 2012 Marshfield, Wisconsin During 2013 After Amendment ton	Jan. 30, 2012 Marshfield, Wisconsin During 2014 After Amendment ton
Long-term Purchase Commitment [Line Items]
Agreement entry date				Nov. 01, 2008		Nov. 01, 2003	Oct. 31, 2008																				Dec. 31, 2003				Jan. 01, 2003							Jul. 31, 2011
Commitment effective date																											2004-01-01		2011-01-01		2003-01-01
Purchase commitment, period							10 years												5 years				10 years				7 years		3 years									5 years
Purchase commitment, commencing date																																					2012-01-30	2011-07-30
Additional purchase commitment, period							10 years												3 years										6 years
Agreement expiration date																		Dec. 31, 2010								Dec. 31, 2010
Purchase obligation percentage of annual requirements																								80.00%				70.00%		70.00%					80.00%
Purchase commitment amount								$ 1,400	$ 1,400	$ 842										$ 2,918	$ 2,834	$ 2,527			$ 3,603	$ 3,646			$ 3,205			$ 2,900	$ 1,687	$ 182		$ 462
Minimum quantity to be purchased											40,000	70,000																											40,000	150,000	100,000	150,000	350,000
Annual rental fee	11,590	9,054	7,693	50
Net book value of property leased	392,659	338,483			258,346
Natural gas purchase commitment													$ 26,003	$ 25,087	$ 16,264	$ 16,265	$ 7,944