Acquisitions (Details)	1 Months Ended	3 Months Ended	12 Months Ended				3 Months Ended	0 Months Ended		1 Months Ended	3 Months Ended		0 Months Ended	1 Months Ended	0 Months Ended			0 Months Ended	12 Months Ended		0 Months Ended		3 Months Ended	12 Months Ended		1 Months Ended			0 Months Ended	1 Months Ended		12 Months Ended			12 Months Ended		12 Months Ended		12 Months Ended				0 Months Ended		0 Months Ended	12 Months Ended
	Jun. 30, 2012 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Mar. 28, 2012 CAD	Dec. 31, 2012 JAMR USD ($)	Oct. 25, 2011 Molycorp Silmet USD ($)	Apr. 02, 2011 Molycorp Silmet USD ($)	Oct. 31, 2011 Molycorp Silmet USD ($)	Dec. 31, 2012 Molycorp Silmet Mg	Oct. 24, 2011 Molycorp Silmet	Apr. 02, 2011 Molycorp Silmet AS Silmet Grupp USD ($)	Apr. 30, 2011 Molycorp Silmet AS Silmet Grupp	Apr. 02, 2011 Molycorp Silmet Treibacher Industries AG USD ($)	Apr. 15, 2011 Molycorp Metals and Alloys (MMA) USD ($)	Apr. 16, 2011 Molycorp Metals and Alloys (MMA) USD ($)	Apr. 15, 2011 Molycorp Metals and Alloys (MMA) Santoku	Dec. 31, 2011 Molycorp Simet and MMA [Member] USD ($)	Dec. 31, 2010 Molycorp Simet and MMA [Member] USD ($)	Jun. 30, 2013 Molycorp Canada USD ($)	Jun. 11, 2012 Molycorp Canada USD ($)	Dec. 31, 2012 Molycorp Canada USD ($)	Dec. 31, 2012 Molycorp Canada USD ($)	Jun. 12, 2012 Molycorp Canada CAD	Jun. 30, 2012 MCP Exchangeco Inc.	Jun. 30, 2012 MCP Exchangeco Inc. Molycorp Canada	Jun. 12, 2012 MCP Exchangeco Inc. Molycorp Canada	Jun. 11, 2012 Molycorp	Jun. 30, 2012 Molycorp Molycorp Canada	Jun. 12, 2012 Molycorp Molycorp Canada	Dec. 31, 2012 Customer relationships Molycorp Silmet	Dec. 31, 2012 Customer relationships Molycorp Canada	Jun. 12, 2012 Customer relationships Molycorp Canada USD ($)	Dec. 31, 2012 Rare earth quotas Molycorp Canada	Jun. 12, 2012 Rare earth quotas Molycorp Canada USD ($)	Dec. 31, 2012 Patents Molycorp Canada	Jun. 12, 2012 Patents Molycorp Canada USD ($)	Dec. 31, 2012 Other Molycorp Canada	Jun. 12, 2012 Other Molycorp Canada USD ($)	Dec. 31, 2012 Secured Debt 10% Senior Securied Notes, net of discount, due June 2020	Jun. 12, 2012 Trade names Molycorp Canada USD ($)	Jun. 11, 2012 As reported Molycorp Canada USD ($)	Jun. 12, 2012 As reported Molycorp Canada USD ($)	Jun. 30, 2013 Adjustment Molycorp Canada USD ($)	Jun. 30, 2013 Purchase Price Allocation Adjustments USD ($)	Dec. 31, 2012 Purchase Price Allocation Adjustments USD ($)
Business Acquisition [Line Items]
Purchase of additional interest by parent, percentage							5.00%
Ownership of subsidiary after purchase of additional interest							95.00%
Purchase of additional interest by parent							$ 15,000,000
Purchase of additional interest by parent, cash portion							5,400,000
Purchase of additional interest by parent, note payable to seller							9,600,000
Purchase of additional interest by parent, note payable to seller, interest rate							3.25%
Cash consideration paid for Molycorp Canada (in CAD per share)																									11.30
Share consideration paid for Molycorp Canada (in shares)																												0.4242			0.4242
Notional amount of derivatives						870,000,000
Common stock issued to acquire the entity (in shares)													1,593,419													507,203	507,203		13,545,426	13,545,426
Cash consideration								10,000,000	9,021,000						9,000,000	17,500,000					908,181,000	908,181,000
Fair value of Molycorp common stock issued	284,100,000								72,653,000							0					284,144,000	284,144,000
Total purchase consideration									81,674,000							17,500,000					1,192,325,000	1,192,325,000																					1,192,325,000		1,192,325,000	0
Cash and cash equivalents									105,000								6,395,000																											317,169,000	317,169,000		0
Restricted cash																																												4,951,000	4,951,000		0
Accounts receivable		101,500,000	101,500,000						5,000,000								4,900,000																											101,470,000	101,470,000		0
Accounts receivable and other current assets									8,626,000								5,474,000
Inventory									37,404,000								11,327,000																											250,989,000	250,989,000		0
Prepaid expenses and other current assets																																												26,893,000	26,893,000		0
Property, plant and equipment									63,393,000								4,512,000																											75,745,000	75,745,000		0
Investments																																												21,019,000	19,928,000		(1,091,000)
Intangibles									2,669,000								0																	341,900,000		78,300,000		39,100,000		8,100,000		14,800,000		482,234,000	482,234,000		0
Deferred tax charges																																												13,435,000	13,435,000		0
Deferred tax assets																																												11,473,000	10,050,000		(1,423,000)
Goodwill									1,455,000								1,977,000																											494,809,000	526,425,000		31,616,000
Other non-current assets																																												4,367,000	4,367,000		0
Accounts payable and accrued expenses									(19,974,000)								(8,989,000)																											(138,576,000)	(138,576,000)		0
Debt																																												(255,338,000)	(255,338,000)		0
Other current liabilities																																												(33,990,000)	(33,990,000)		0
Deferred tax liabilities									0								3,196,000																											(154,309,000)	(148,429,000)		5,880,000
Long-term debt									(3,184,000)								0
Other non-current liabilities																																												(14,255,000)	(14,255,000)		0
Non-controlling interests									(8,820,000)								0																											(15,761,000)	(50,743,000)		(34,982,000)
Weighted average useful life																																	15 years		11 years		2 years		12 years
Goodwill, additional impairment loss from final purchase price allocation																							31,600,000
Impairment of goodwill		289,900,000	289,894,000	0	0																			287,900,000
Business Acquisition, Transaction Costs [Abstract]
Corporate development: Legal, accounting and advisory fees			19,796,000	5,912,000	0														2,100,000					16,498,000
Other expenses: Contingent forward contract loss																								37,589,000
Interest expense: Bridge loan fee																								7,937,000
Unaudited proforma
Revenues		307,918,000	863,728,000	1,196,876,000															430,305,000	85,549,000
Net Income (Loss)		(338,347,000)	(463,716,000)	241,903,000															105,397,000	(30,920,000)
Net Income (Loss) Attributable To Molycorp		(344,173,000)	(473,249,000)	231,772,000															104,590,000	(31,329,000)
EPS Basic (in dollars per share)		$ (3.21)	$ (4.53)	$ 2.66															$ 1.13	$ (0.50)
Other actual and pro forma information
Pro forma intercompany revenue																			69,100,000
Pro forma intercompany net income (loss)																			28,000,000
Purchase price variance capitalized																			1,100,000
Finite-Lived Assets, Useful Life, Minimum			2 years
Finite-Lived Assets, Useful Life, Maximum			30 years
Interest rate																																									10.00%
Direct Transaction Expenses Excluded from Nonrecurring Expense			115,200,000
Recognized Transaction Costs			62,000,000
Interest acquired (as a percent)									90.023%			9.977%	80.00%		10.023%
Other disclosures
Contractual value of shares issued to acquire the entity													80,000,000
Number of consecutive trading days considered for calculation of closing price													20 days
Discount percentage deducted from common stock price														23.00%
Adjustments to Additional Paid in Capital										$ 400,000
Useful life																																15 years
Increase in rare earth production capacity (in mt)											3,000
Period of marketing and distribution agreement (in years)																		5 years
Period of rare earth products purchase and supply agreement (in years)																		2 years