Condensed Consolidated Statements of Operations and Comprehensive Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 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
Income Statement [Abstract]
Revenues	$ 134,259		$ 205,604		$ 104,577		$ 84,470		$ 132,905		$ 138,050		$ 99,615		$ 26,261		$ 528,910	$ 396,831	$ 35,157
Costs of sales:
Costs excluding depreciation and amortization																	(480,655)	(164,351)	(28,797)
Depreciation and amortization																	(30,910)	(13,539)	(5,694)
Gross profit	(20,473)		10,864		(4,073)		31,027		70,272		82,392		56,692		9,584		17,345	218,941	666
Operating expenses:
Selling, general and administrative																	(113,669)	(50,757)	(45,175)
Corporate development																	(19,796)	(5,912)	0
Depreciation, amortization and accretion																	(22,215)	(1,688)	(1,231)
Research and development																	(27,796)	(7,718)	(2,338)
Impairment of goodwill and other long-lived assets																	(301,755)	0	(3,100)
Operating (loss) income																	(467,886)	152,866	(51,178)
Other (expense) income:
Other (expense) income																	(38,798)	(153)	155
Foreign exchange gain (loss), net																	2,872	(5,415)	0
Interest (expense) income, net of capitalized interest																	(22,116)	(388)	249
Total other expense																	(58,042)	(5,956)	404
(Loss) income before income taxes and equity earnings	(382,779)		(43,745)		(93,970)		(5,434)		42,607		64,157		42,143		(1,999)		(525,928)	146,910	(50,774)
Income tax benefit (expense)																	54,075	(28,576)	0
Equity in results of affiliates																	(3,490)	0	0
Net (loss) income	(389,490)		(15,451)		(66,924)		(3,478)		26,674		45,101		48,755		(2,198)		(475,343)	118,334	(50,774)
Net income attributable to noncontrolling interest																	(5,826)	(808)	0
Net (loss) income attributable to Molycorp stockholders	(391,196)		(18,891)		(67,604)		(3,478)		26,579		45,356		47,787		(2,198)		(481,169)	117,526	(50,774)
Other comprehensive income:
Foreign currency translation adjustments																	(952)	(8,481)	0
Comprehensive (loss) income																	(476,295)	109,853	(50,774)
Comprehensive (loss) income attributable to:
Molycorp stockholders																	(470,469)	109,468	(50,774)
Noncontrolling interest																	(5,826)	385	0
Comprehensive (loss) income																	$ (476,295)	$ 109,853	$ (50,774)
(Loss) income per share of common stock (Note 17):
Basic (in dollars per share)	$ (3.16)	[1]	$ (0.19)	[1]	$ (0.71)	[1]	$ (0.07)	[1]	$ 0.27	[1]	$ 0.51	[1]	$ 0.54	[1]	$ (0.04)	[1]	$ (4.60)	$ 1.29	$ (0.81)
Diluted (in dollars per share)	$ (3.16)	[1]	$ (0.19)	[1]	$ (0.71)	[1]	$ (0.07)	[1]	$ 0.26	[1]	$ 0.49	[1]	$ 0.53	[1]	$ (0.04)	[1]	$ (4.60)	$ 1.27	$ (0.81)

[1] The sum of the quarterly income (loss) per share may be different than the per share amount for the year as the calculation for each quarter is based on the weighted average shares outstanding for that period.