Property, Plant and Equipment, net (Details) (USD $)	3 Months Ended		12 Months Ended
	Dec. 31, 2012		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Additions, Gross of Capitalized Interest			$ 902,300,000		$ 416,700,000
Capitalized interest related to plant modernization and other capitalized costs			59,300,000		7,500,000
Depreciation expense			20,900,000		14,000,000		6,000,000
Property, plant and equipment at cost	1,589,235,000		1,589,235,000		584,865,000
Less accumulated depreciation	(44,931,000)		(44,931,000)		(23,237,000)
Property, plant and equipment, net	1,544,304,000		1,544,304,000		561,628,000
Impairment of long-lived assets to be disposed of	5,900,000		5,900,000				3,100,000
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	12,475,000		12,475,000		11,059,000
Land improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	63,269,000		63,269,000		15,748,000
Useful life			15 years
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	237,379,000		237,379,000		23,677,000
Plant and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	194,934,000		194,934,000		68,441,000
Vehicles
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	2,842,000		2,842,000		1,235,000
Useful life			7 years
Computer software
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	9,528,000		9,528,000		3,002,000
Useful life			5 years
Furnitures and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	1,116,000		1,116,000		464,000
Useful life			5 years
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	1,011,541,000	[1]	1,011,541,000	[1]	436,547,000	[1]
Capital Leases
Property, Plant and Equipment [Line Items]
Capital Leased Assets, Gross	15,658,000		15,658,000		0
Less accumulated depreciation	(900,000)		(900,000)
Useful life			10 years
Mineral properties
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	24,327,000		24,327,000		24,692,000
Exploration rights
Property, Plant and Equipment [Line Items]
Property, plant and equipment at cost	16,166,000		16,166,000		0
Minimum | Buildings and improvements
Property, Plant and Equipment [Line Items]
Useful life			4 years
Minimum | Plant and equipment
Property, Plant and Equipment [Line Items]
Useful life			2 years
Maximum | Buildings and improvements
Property, Plant and Equipment [Line Items]
Useful life			40 years
Maximum | Plant and equipment
Property, Plant and Equipment [Line Items]
Useful life			15 years
Rare Metals
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets to be disposed of	2,000,000
Molycorp Mountain Pass facility
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets to be disposed of	$ 3,800,000

[1] Represents costs incurred at the Molycorp Mountain Pass facility and all other capital projects. See Note 3.