Condensed Consolidated Statement of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Total Molycorp Stockholders	Common Stock	Series A Mandatory Convertible Preferred Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Surplus (Deficit) Accumulated During the Development Stage	Noncontrolling interest	Class A Common Stock
Balance at Jun. 12, 2008
Increase (Decrease) in Stockholders' Equity
Issuance of shares for cash on various dates at $2.60, $4.68, $2.37 per share in 2010, 2009, and 2008, respectively	$ 92,000	$ 92,000			$ 91,961				$ 39
Issuance of shares for cash on various dates at $2.60, $4.68, $2.37 per share in 2010, 2009, and 2008, respectively (in shares)									38,762,268
Stock-based compensation, at $2.24 per share based on a set dollar amount for November 6, 2008 (Note 17)	150	150			150
Stock-based compensation, at $2.24 per share based on a set dollar amount for November 6, 2008 (Note 17) (in shares)									66,957
Net (loss) income	(14,074)	(14,074)					(14,074)
Balance at Dec. 31, 2008	78,076	78,076			92,111		(14,074)		39
Balance (in shares) at Dec. 31, 2008									38,829,225
Increase (Decrease) in Stockholders' Equity
Issuance of shares for cash on various dates at $2.60, $4.68, $2.37 per share in 2010, 2009, and 2008, respectively	18,004	18,004			18,000				4
Issuance of shares for cash on various dates at $2.60, $4.68, $2.37 per share in 2010, 2009, and 2008, respectively (in shares)									3,844,858
Conversion of short term borrowings from member and related accrued interest in common shares on November 15, 2009 at $2.96 per share based on a contractual price	6,831	6,831			6,829				2
Conversion of short term borrowings from member and related accrued interest in common shares on November 15, 2009 at $2.96 per share based on a contractual price (in shares)									2,303,033
Exercise of employee options on February 1, 2010 and September 4, 2009 at $2.37 per share	50	50			50
Exercise of employee options on February 1, 2010 and September 4, 2009 at $2.37 per share (in shares)									21,069
Stock-based compensation, at $2.24 per share based on a set dollar amount for November 6, 2008 (Note 17)	241	241			241
Net (loss) income	(28,587)	(28,587)					(28,587)
Balance at Dec. 31, 2009	74,615	74,615			117,231		(42,661)		45
Balance (in shares) at Dec. 31, 2009									44,998,185
Increase (Decrease) in Stockholders' Equity
Issuance of shares for cash on various dates at $2.60, $4.68, $2.37 per share in 2010, 2009, and 2008, respectively	15,000	15,000			14,994				6
Issuance of shares for cash on various dates at $2.60, $4.68, $2.37 per share in 2010, 2009, and 2008, respectively (in shares)									5,767,670
Exercise of employee options on February 1, 2010 and September 4, 2009 at $2.37 per share	300	300			300
Exercise of employee options on February 1, 2010 and September 4, 2009 at $2.37 per share (in shares)									126,405
Conversion of Class A stock to common stock in conjunction with the IPO on August 3, 2010			51						(51)
Conversion of Class A stock to common stock in conjunction with the IPO on August 3, 2010 (in shares)			50,892,260						(50,892,260)
Sale of shares of common stock at $14.00 per share in IPO 2010, net of offering costs of $29.2 million	378,633	378,633	29		378,604
Sale of shares of common stock at $14.00 per share in IPO 2010, net of offering costs of $29.2 million (in shares)			29,128,700
Conversion of Class B stock to common stock in conjunction with the IPO on August 3, 2010	28,663	28,663	2		28,661
Conversion of Class B stock to common stock in conjunction with the IPO on August 3, 2010 (in shares)			2,232,740
Stock-based compensation, at $2.24 per share based on a set dollar amount for November 6, 2008 (Note 17)	76	76			76
Stock-based compensation, at $2.24 per share based on a set dollar amount for November 6, 2008 (Note 17) (in shares)			37,500
Net (loss) income	(50,774)	(50,774)					(50,774)
Balance at Dec. 31, 2010	446,513	446,513	82		539,866		(93,435)
Balance (in shares) at Dec. 31, 2010			82,291,200
Increase (Decrease) in Stockholders' Equity
Sale of Series A mandatory convertible preferred stock on February 16, 2011 at $100.00 per share, net of underwriting	199,642	199,642		2	199,640
Sale of Series A mandatory convertible preferred stock on February 16, 2011 at $100.00 per share, net of underwriting (in shares)				2,070,000
Stock-based compensation, at $2.24 per share based on a set dollar amount for November 6, 2008 (Note 17)	4,671	4,671			4,671
Stock-based compensation, at $2.24 per share based on a set dollar amount for November 6, 2008 (Note 17) (in shares)			11,424
Issuance of shares for interest in Molycorp Silmet on April 1, 2011 at $45.60 per share	81,475	72,655	2		72,653			8,820
Issuance of shares for interest in Molycorp Silmet on April 1, 2011 at $45.60 per share (in shares)			1,593,419
Component of convertible debt	36,227	36,227			36,227
Deferred taxes on component of convertible debt	(14,138)	(14,138)			(14,138)
Net (loss) income	118,334	117,526					117,526	808
Preferred dividends	(9,013)	(9,013)					(9,013)
Other comprehensive income	(8,481)	(8,058)				(8,058)		(423)
Acquisition of noncontrolling interest	(10,000)	(795)			(372)	(423)		(9,205)
Balance at Dec. 31, 2011	845,230	845,230	84	2	838,547	(8,481)	15,078
Balance (in shares) at Dec. 31, 2011			83,896,043	2,070,000
Increase (Decrease) in Stockholders' Equity
Stock-based compensation, at $2.24 per share based on a set dollar amount for November 6, 2008 (Note 17)	1,408	1,408			1,408
Issuance of shares for investment from Molymet on March 8, 2012 at $31.218 per share, net of stock issuance costs (Note 15)	390,093	390,093	12		390,081
Issuance of shares for investment from Molymet on March 8, 2012 at $31.218 per share, net of stock issuance costs (Note 15) (in shares)			12,500,000
Net (loss) income	(3,478)	(3,478)					(3,478)
Preferred dividends	(2,846)	(2,846)					(2,846)
Other comprehensive income	2,530	2,530				2,530
Balance at Mar. 31, 2012	$ 1,232,937	$ 1,232,937	$ 96	$ 2	$ 1,230,036	$ (5,951)	$ 8,754
Balance (in shares) at Mar. 31, 2012			96,396,043	2,070,000