Concentrations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		46 Months Ended		3 Months Ended							3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012	Mar. 31, 2012 Sales MMA NdFeB alloys	Mar. 31, 2012 Sales Molycorp Mountain Pass facility	Mar. 31, 2012 Sales Molycorp Mountain Pass facility Lanthanum products	Mar. 31, 2011 Sales Molycorp Mountain Pass facility Lanthanum products	Mar. 31, 2012 Sales Molycorp Mountain Pass facility Cerium products	Mar. 31, 2011 Sales Molycorp Mountain Pass facility Cerium products	Mar. 31, 2012 Sales Molycorp Mountain Pass facility Didymium, Neodymium and Praseodymium products	Mar. 31, 2011 Sales Molycorp Mountain Pass facility Didymium, Neodymium and Praseodymium products	Mar. 31, 2012 Sales Limited Number of Customers customer	Mar. 31, 2012 Sales Limited Number of Customers Molycorp Silmet customer	Mar. 31, 2012 Sales Limited Number of Customers MMA customer	Jun. 30, 2012 Sales Limited Number of Customers MMA Customer one	Mar. 31, 2012 Sales Limited Number of Customers Molycorp Mountain Pass facility customer	Mar. 31, 2011 Sales Limited Number of Customers Molycorp Mountain Pass facility customer	Mar. 31, 2012 Sales Limited Number of Customers Molycorp Mountain Pass facility Customer one	Mar. 31, 2011 Sales Limited Number of Customers Molycorp Mountain Pass facility Customer one	Mar. 31, 2012 Sales Limited Number of Customers Molycorp Mountain Pass facility Customer two	Mar. 31, 2011 Sales Limited Number of Customers Molycorp Mountain Pass facility Customer two	Mar. 31, 2011 Sales Limited Number of Customers Molycorp Mountain Pass facility Customer three	Mar. 31, 2012 Sales Limited Number of Products Molycorp Silmet product
Concentrations
Percentage of sales to total sales threshold					10.00%							10.00%
Percentage of sales				19.00%		46.00%	44.00%	1.00%	34.00%	53.00%	18.00%	20.00%	57.00%	88.00%		98.00%
Percentage of entity's sales															20.00%
Number of rare metal products																							2
Sales, net of intercompany transactions	$ 84,470	$ 26,261	$ 525,688											$ 16,600				$ 20,400	$ 7,800	$ 17,200	$ 6,200	$ 5,800
Number of customers representing a specified percentage of sales												2	4			3	3
Number of customers representing a specified percentage of sales, net of intercompany sales														1
Percentage of sales of total sales																	75.00%