Concentrations (Details) (USD $)	3 Months Ended								12 Months Ended				7 Months Ended	9 Months Ended		12 Months Ended												9 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Product Concentration Chemicals and Oxides Cerium products	Dec. 31, 2012 Product Concentration Magnetic Materials and Alloys Neo Powders	Dec. 31, 2011 Product Concentration Magnetic Materials and Alloys NdFeB Alloys	Dec. 31, 2012 Product Concentration Resources	Dec. 31, 2011 Product Concentration Resources Lanthanum products	Dec. 31, 2010 Product Concentration Resources Lanthanum products	Dec. 31, 2011 Product Concentration Resources Cerium products	Dec. 31, 2010 Product Concentration Resources Cerium products	Dec. 31, 2011 Product Concentration Resources Neodymium and Praseodymium products	Dec. 31, 2010 Product Concentration Resources Neodymium and Praseodymium products	Dec. 31, 2012 Product Concentration Customers Concentration	Dec. 31, 2011 Product Concentration Customers Concentration Hitachi Metals Ltd.	Dec. 31, 2010 Product Concentration Customers Concentration Mitsubishi Unimetals USA	Dec. 31, 2010 Product Concentration Customers Concentration W.R. Grace & Co.—Conn.	Dec. 31, 2010 Product Concentration Customers Concentration Chuden Rare Earth Co. Ltd.	Dec. 31, 2010 Product Concentration Customers Concentration Shin-Etsu Chemical Co.	Dec. 31, 2011 Molycorp Tolleson Product Concentration Customers Concentration Santoku
Concentrations
Entity-wide revenue, major customers												15.00%	25.00%	11.00%		23.00%	39.00%	11.00%	29.00%	26.00%	26.00%							12.00%
Percentage of sales to total sales threshold															15.00%
Sales, net of intercompany transactions	$ 134,259,000	$ 205,604,000	$ 104,577,000	$ 84,470,000	$ 132,905,000	$ 138,050,000	$ 99,615,000	$ 26,261,000	$ 528,910,000	$ 396,831,000	$ 35,157,000											$ 0	$ 92,200,000	$ 8,500,000	$ 7,400,000	$ 5,400,000	$ 4,000,000	$ 48,800,000