Commitments and Contingencies Narrative (Details) (USD $)				12 Months Ended
	Dec. 31, 2012 jurisdiction employee	Feb. 29, 2012 lawsuit	Dec. 31, 2012 Molycorp Canada	Dec. 31, 2012 Office space, trailers and certain equipment	Dec. 31, 2011 Office space, trailers and certain equipment	Dec. 31, 2010 Office space, trailers and certain equipment	Dec. 31, 2012 Employees covered by collective bargaining agreement under facility Workforce Molycorp Mountain Pass facility employee	Dec. 31, 2012 Molycorp Silmet Employees covered by collective bargaining agreement under facility Workforce employee
Plant Modernization and Expansion Commitments
Operating leases rent expense net				$ 4,100,000	$ 700,000	$ 500,000
Other purchase obligations	14,017,000		7,500,000
Number of employees	2,700						236	176
Concentration risk (as a percent)							61.00%	29.00%
Surety bonds placed to secure the closure and reclamation obligations	$ 28,700,000
Number of stockholder derivative lawsuits		7
Number of different jurisdictions in which lawsuits have been filed	3