Condensed Consolidating Statement of Operations and Comprehensive Income (Details) (USD $)	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
Condensed Financial Statements, Captions [Line Items]
Revenues	$ 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
Costs of sales:
Costs excluding depreciation and amortization									(480,655,000)	(164,351,000)	(28,797,000)
Depreciation and amortization									(30,910,000)	(13,539,000)	(5,694,000)
Gross profit	(20,473,000)	10,864,000	(4,073,000)	31,027,000	70,272,000	82,392,000	56,692,000	9,584,000	17,345,000	218,941,000	666,000
Operating expenses:
Selling, general and administrative									(113,669,000)	(50,757,000)	(45,175,000)
Corporate development									(19,796,000)	(5,912,000)	0
Depreciation, amortization and accretion									(22,215,000)	(1,688,000)	(1,231,000)
Research and development									(27,796,000)	(7,718,000)	(2,338,000)
Impairment of goodwill and other long-lived assets									(301,755,000)	0	(3,100,000)
Operating (loss) income									(467,886,000)	152,866,000	(51,178,000)
Other (expense) income:
Other (expense) income									(38,798,000)	(153,000)	155,000
Foreign exchange gain (loss), net									2,872,000	(5,415,000)	0
Interest (expense) income, net of capitalized interest									(22,116,000)	(388,000)	249,000
Interest income (expense) from intercompany notes									0	0
Equity earnings from consolidated subsidiaries									0	0	0
Total other expense									(58,042,000)	(5,956,000)	404,000
(Loss) income before income taxes and equity earnings	(382,779,000)	(43,745,000)	(93,970,000)	(5,434,000)	42,607,000	64,157,000	42,143,000	(1,999,000)	(525,928,000)	146,910,000	(50,774,000)
Income tax benefit (expense)									54,075,000	(28,576,000)	0
Equity in results of affiliates									(3,490,000)	0	0
Net (loss) income	(389,490,000)	(15,451,000)	(66,924,000)	(3,478,000)	26,674,000	45,101,000	48,755,000	(2,198,000)	(475,343,000)	118,334,000	(50,774,000)
Net income attributable to noncontrolling interest									(5,826,000)	(808,000)	0
Net (loss) income attributable to Molycorp stockholders	(391,196,000)	(18,891,000)	(67,604,000)	(3,478,000)	26,579,000	45,356,000	47,787,000	(2,198,000)	(481,169,000)	117,526,000	(50,774,000)
Other comprehensive income:
Foreign currency translation adjustments									(952,000)	(8,481,000)	0
Comprehensive (loss) income									(476,295,000)	109,853,000	(50,774,000)
Comprehensive (loss) income attributable to:
Molycorp stockholders									(470,469,000)	109,468,000	(50,774,000)
Noncontrolling interest									(5,826,000)	385,000	0
Parent
Condensed Financial Statements, Captions [Line Items]
Revenues									0	0	0
Costs of sales:
Costs excluding depreciation and amortization									0	0	0
Depreciation and amortization									0	0	0
Gross profit									0	0	0
Operating expenses:
Selling, general and administrative									46,000	(7,000)	(436,000)
Corporate development									(46,000)	0
Depreciation, amortization and accretion									0	0	0
Research and development									0	0	0
Impairment of goodwill and other long-lived assets									0		0
Operating (loss) income									0	(7,000)	(436,000)
Other (expense) income:
Other (expense) income									(37,589,000)	0	0
Foreign exchange gain (loss), net									0	0
Interest (expense) income, net of capitalized interest									(18,118,000)	(499,000)	249,000
Interest income (expense) from intercompany notes									25,157,000	424,000
Equity earnings from consolidated subsidiaries									(456,649,000)	117,608,000	(50,587,000)
Total other expense									(487,199,000)	117,533,000	(50,338,000)
(Loss) income before income taxes and equity earnings									(487,199,000)	117,526,000
Income tax benefit (expense)									6,030,000	0
Equity in results of affiliates									0
Net (loss) income									(481,169,000)	117,526,000	(50,774,000)
Net income attributable to noncontrolling interest									0	0
Net (loss) income attributable to Molycorp stockholders									(481,169,000)	117,526,000
Other comprehensive income:
Foreign currency translation adjustments									0	0
Comprehensive (loss) income									(481,169,000)	117,526,000
Comprehensive (loss) income attributable to:
Molycorp stockholders									(481,169,000)	117,526,000
Noncontrolling interest										0
Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Revenues									139,257,000	365,490,000	35,157,000
Costs of sales:
Costs excluding depreciation and amortization									(153,461,000)	(158,951,000)	(28,797,000)
Depreciation and amortization									(12,094,000)	(9,411,000)	(5,694,000)
Gross profit									(26,298,000)	197,128,000	666,000
Operating expenses:
Selling, general and administrative									(86,493,000)	(48,296,000)	(44,739,000)
Corporate development									(19,750,000)	(5,912,000)
Depreciation, amortization and accretion									(2,220,000)	(1,378,000)	(1,231,000)
Research and development									(12,984,000)	(7,718,000)	(2,338,000)
Impairment of goodwill and other long-lived assets									(5,747,000)		(3,100,000)
Operating (loss) income									(153,492,000)	133,824,000	(50,742,000)
Other (expense) income:
Other (expense) income									(328,000)	(153,000)	155,000
Foreign exchange gain (loss), net									0	0
Interest (expense) income, net of capitalized interest									(3,496,000)	248,000	0
Interest income (expense) from intercompany notes									3,152,000	(296,000)
Equity earnings from consolidated subsidiaries									(23,205,000)	12,485,000	0
Total other expense									(23,877,000)	12,284,000	155,000
(Loss) income before income taxes and equity earnings									(177,369,000)	146,108,000
Income tax benefit (expense)									53,840,000	(28,500,000)
Equity in results of affiliates									(2,439,000)
Net (loss) income									(125,968,000)	117,608,000	(50,587,000)
Net income attributable to noncontrolling interest									0	0
Net (loss) income attributable to Molycorp stockholders									(125,968,000)	117,608,000
Other comprehensive income:
Foreign currency translation adjustments									0	0
Comprehensive (loss) income									(125,968,000)	117,608,000
Comprehensive (loss) income attributable to:
Molycorp stockholders									(125,968,000)	117,608,000
Noncontrolling interest										0
Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Revenues									415,165,000	100,398,000
Costs of sales:
Costs excluding depreciation and amortization									(352,706,000)	(74,457,000)
Depreciation and amortization									(18,816,000)	(4,128,000)
Gross profit									43,643,000	21,813,000
Operating expenses:
Selling, general and administrative									(27,222,000)	(2,454,000)
Corporate development									0	0
Depreciation, amortization and accretion									(19,995,000)	(310,000)
Research and development									(14,812,000)	0
Impairment of goodwill and other long-lived assets									(296,008,000)
Operating (loss) income									(314,394,000)	19,049,000
Other (expense) income:
Other (expense) income									(881,000)	0
Foreign exchange gain (loss), net									2,872,000	(5,415,000)
Interest (expense) income, net of capitalized interest									(502,000)	(137,000)
Interest income (expense) from intercompany notes									(28,309,000)	(128,000)
Equity earnings from consolidated subsidiaries									0	0
Total other expense									(26,820,000)	(5,680,000)
(Loss) income before income taxes and equity earnings									(341,214,000)	13,369,000
Income tax benefit (expense)									(5,795,000)	(76,000)
Equity in results of affiliates									(1,051,000)
Net (loss) income									(348,060,000)	13,293,000
Net income attributable to noncontrolling interest									(5,826,000)	(808,000)
Net (loss) income attributable to Molycorp stockholders									(353,886,000)	12,485,000
Other comprehensive income:
Foreign currency translation adjustments									(952,000)	(8,481,000)
Comprehensive (loss) income									(349,012,000)	4,812,000
Comprehensive (loss) income attributable to:
Molycorp stockholders									(343,186,000)	4,427,000
Noncontrolling interest									(5,826,000)	385,000
Eliminations
Condensed Financial Statements, Captions [Line Items]
Revenues									(25,512,000)	(69,057,000)	0
Costs of sales:
Costs excluding depreciation and amortization									25,512,000	69,057,000	0
Depreciation and amortization									0	0	0
Gross profit									0	0	0
Operating expenses:
Selling, general and administrative									0	0	0
Corporate development									0	0
Depreciation, amortization and accretion									0	0	0
Research and development									0	0	0
Impairment of goodwill and other long-lived assets									0		0
Operating (loss) income									0	0	0
Other (expense) income:
Other (expense) income									0	0	0
Foreign exchange gain (loss), net									0	0
Interest (expense) income, net of capitalized interest									0	0	0
Interest income (expense) from intercompany notes									0	0
Equity earnings from consolidated subsidiaries									479,854,000	(130,093,000)	50,587,000
Total other expense									479,854,000	(130,093,000)	50,587,000
(Loss) income before income taxes and equity earnings									479,854,000	(130,093,000)
Income tax benefit (expense)										0
Net (loss) income									479,854,000	(130,093,000)	50,587,000
Net income attributable to noncontrolling interest									0	0
Net (loss) income attributable to Molycorp stockholders									479,854,000	(130,093,000)
Other comprehensive income:
Foreign currency translation adjustments										0
Comprehensive (loss) income									479,854,000	(130,093,000)
Comprehensive (loss) income attributable to:
Molycorp stockholders									479,854,000	(130,093,000)
Noncontrolling interest										$ 0