Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2012	Feb. 28, 2013	Jun. 30, 2012
Document and Entity Information [Abstract]
Entity Registrant Name	Molycorp, Inc.
Entity Central Index Key	0001489137
Document Type	10-K/A
Document Period End Date	Dec. 31, 2012
Amendment Flag	true
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		188,581,613
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	FY
Amendment Description	In light of a material weakness that resulted in a restatement of our unaudited condensed consolidated financial statements for the three months ended March 31, 2013, we re-evaluated our conclusion regarding the effectiveness of our internal control over financial reporting as of December 31, 2012.
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Public Float			$ 1,504,675,694