Income Taxes Narrative (Details) (USD $)	3 Months Ended	12 Months Ended						3 Months Ended			0 Months Ended						12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Statute of limitations expiration and possible settements with taxing authorities	Dec. 31, 2012 IRS	Dec. 31, 2012 State	Sep. 30, 2012 Domestic Tax Authority	Sep. 30, 2012 Foreign Tax Authority	Dec. 31, 2012 Foreign Tax Authority	Jun. 11, 2012 Molycorp Canada	Dec. 31, 2012 Expiring in 2024	Dec. 31, 2012 Expiring in 2031 and 2032	Dec. 31, 2012 Expiring in 2031	Dec. 31, 2012 Expiring in 2032	Dec. 31, 2012 Indefinite Carryforward	Dec. 31, 2012 Minimum	Dec. 31, 2012 Maximum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Goodwill and intangible asset impairment	$ 295,900,000
Deferred tax liabilities, net	150,886,000	150,886,000	20,255,000
Valuation allowance	20,631,000	20,631,000	0
Increases in uncertain tax positions resulting from acquisition		5,700,000									20,100,000
Effective income tax rate		10.30%	19.50%	0.00%
Income tax expense		54,075,000	(28,576,000)	0
Foreign subsidiary earnings and withholding taxes	32,637,000	32,637,000	0
Deferred income tax expense due to elimination of intercompany balances and transactions	9,400,000	9,400,000
Income tax payable due to elimination of intercompany balances and transactions	9,400,000	9,400,000
Federal tax rate			35.00%
Tax credit carryforward	12,100,000	12,100,000											10,500,000	3,100,000	7,400,000	1,600,000
Operating Loss Carryforwards						85,400,000	86,500,000			96,700,000		29,800,000			55,600,000
Income tax holiday period																	5 years	10 years
Statute of limitations closures		1,406,000	0					1,400,000
Settlements		13,740,000	0						13,700,000
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, lower bound					4,000,000
Significant change in unrecognized tax benefits is reasonably possible, estimated range of change, higher bound					$ 6,000,000