Subsequent Events (Details) (USD $)	12 Months Ended			0 Months Ended	1 Months Ended	0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jan. 30, 2013 Subsequent Event	Feb. 28, 2013 Subsequent Event	Jan. 30, 2013 5.50% Convertible Senior Notes due 2018 Convertible Debt Subsequent Event	Jan. 30, 2013 Officers, Directors and Other Related Parties Subsequent Event	Jan. 30, 2013 Officers, Directors and Other Related Parties 5.50% Convertible Senior Notes due 2018 Convertible Debt Subsequent Event
Subsequent Events
Stock issued during the period, shares				37,500,000
Offering price per share				$ 6
Debt instrument, face amount						$ 150,000,000
Interest rate						5.50%
Underwriter option to purchase additional shares, time period				30 days
Underwriters Option to purchase within 30 days				5,625,000
Offering price per share, underwriters				$ 6
Underwriter option to purchase additional principal						22,500,000
Underwriter fees				6.00%
Shares purchased by related parties							15,016,666
Proceeds from issuance of long-term debt from related parties								20,500,000
Proceeds from issuance of long-term debt						165,600,000
Net proceeds from sale of common stock	$ 132,130,000	$ 0	$ 378,633,000	$ 248,600,000
Convertible conversion ratio						138.8889
Convertible ratio, price per share						$ 7.20
Percentage of last reported sale price of Molycorp common stock over conversion price on or after September 1, 2016 giving right to the Notes redemption						130.00%
Trading days during any 30 consecutive trading day period ending on, and including, the trading day immediately preceding the date on which Molycorp provides notice of redemption						20 days
Consecutive trading day period ending on, and including, the trading day immediately preceding the date on which Molycorp provides notice of redemption						30 days
Number of borrowed shares				7,666,666
Number of borrowed shares offered in registered public offering				6,333,333
Number of borrowed shares offered in registered public offering, price per share				$ 6
Cash dividend declared (in dollars per share)					$ 1.375