Capital Requirements (Details) (USD $)	12 Months Ended							35 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2012 JAMR	Oct. 09, 2013 Subsequent Event	Jun. 30, 2013 Subsequent Event	Jun. 30, 2013 Subsequent Event Molycorp Mountain Pass facility Mg	Jun. 30, 2013 Subsequent Event All operating segments	Jun. 30, 2013 Subsequent Event JAMR
Capital Expenditures [Line Items]
Total current estimated costs								$ 1,550,000,000
Annual design capacity (in metric tonnes)								19,050
Capital expenditures	791,469,000	302,180,000	33,129,000					1,300,000,000
Expected Future Capital Expenditures, Remainder of Fiscal Year								130,000,000
Cash and cash equivalents	227,790,000	418,855,000	316,430,000	6,929,000			264,200,000
Estimated capital expenditures in 2013								40,000,000
Expected Future Capital Expenditures, Estimated Capital Expenditures in Two Years								70,000,000
Estimated expenditures on other maintenance and expansion capital expenditures in 2013									17,000,000
Purchase of additional interest by parent, note payable to seller					9,600,000					6,000,000
Preferred stock dividend payments, if declared in the remainder of the year.							5,600,000
Effect of 15% decrease in REEs mark price on expected cash flow								8,000,000
Effect of 15% decrease in REEs volume on expected cash flow								30,000,000
Molymet's agreement to purchase Molycorp's common stock						$ 50,000,000