Stockholders' Equity (Details) (USD $)	0 Months Ended	1 Months Ended	3 Months Ended	12 Months Ended			0 Months Ended	12 Months Ended	7 Months Ended	12 Months Ended		0 Months Ended	1 Months Ended				12 Months Ended				1 Months Ended	0 Months Ended		3 Months Ended
	Feb. 16, 2011	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Mar. 08, 2012 Molymet	Dec. 31, 2012 Molymet	Dec. 31, 2012 Common Stock	Dec. 31, 2012 Common Stock	Dec. 31, 2011 Common Stock	Feb. 16, 2011 Series A Mandatory Convertible Preferred Stock	Nov. 30, 2012 Series A Mandatory Convertible Preferred Stock	Aug. 31, 2012 Series A Mandatory Convertible Preferred Stock	May 31, 2012 Series A Mandatory Convertible Preferred Stock	Feb. 29, 2012 Series A Mandatory Convertible Preferred Stock	Dec. 31, 2012 Series A Mandatory Convertible Preferred Stock	Dec. 31, 2011 Series A Mandatory Convertible Preferred Stock	Feb. 16, 2011 Series A Mandatory Convertible Preferred Stock Minimum	Feb. 16, 2011 Series A Mandatory Convertible Preferred Stock Maximum	Jun. 30, 2012 MCP Exchangeco Inc.	Jun. 11, 2012 Molycorp	Dec. 31, 2012 Convertible Debt 6.00% Convertible Notes	Dec. 31, 2012 Exploration rights	Dec. 31, 2011 Exploration rights
Stockholders' Equity
Shares outstanding									138,773,538	138,773,538	83,896,043						2,070,000	2,070,000
Preferred Stock, Liquidation Preference Per Share												$ 100.00
Dividend rate												5.50%					5.50%	5.50%
Property, plant and equipment at cost			$ 1,589,235,000	$ 1,589,235,000	$ 584,865,000																			$ 16,166,000	$ 0
Issuance of shares for investment in mining property																								788,410
Sale of stock, price per share																								$ 10.147
Payments to acquire exploration rights			8,200,000	8,167,000	0	0
Number of borrowed shares									13,800,000	13,800,000
Stock issued during the period, shares							12,500,000		13,800,000	99,723
Share price (in dollars per share)									$ 10	$ 10
Underwriting discounts and commissions									6.00%
Flat fee paid to underwriters									1,500,000
Primary shares purchased by insiders									7,090,000
Preferred stock, par value			$ 0.001	$ 0.001								$ 0.001
Preferred stock, shares issued												1,800,000
Mandatory convertible preferred stock price per share												$ 100
Net proceeds from sale of preferred stock	199,600,000			0	199,642,000	0
Underwriter option to purchase additional shares												270,000
Preferred shares issued upon conversion																			1.6667	2
Interest rate																							6.00%
Common stock issued to acquire the entity (in shares)																					507,203	13,545,426
Fair value of common stock		284,100,000
Exchangeable shares converted									340,196
Issuance of shares				132,130,000		15,000,000	390,100,000	390,093,000
Stock issuance costs						29,200,000	100,000
Price per share of common stock issued for investment							$ 31.218
Number of consecutive trading days to calculate common stock price							20 days
Premium percentage added to common stock price							10.00%
Cash dividend declared (in dollars per share)													$ 1.375	$ 1.375	$ 1.375	$ 1.375
Cash dividend declared and paid				$ 11,385,000	$ 9,015,000	$ 0											$ 11,400,000	$ 9,000,000