Mineral Properties and Development Costs (Details) (USD $)	3 Months Ended
Mar. 31, 2012
Mineral Properties and Development Costs
Capitalized depletion costs in in work-in-process inventory	$ 21,000

Represents depletion costs capitalized in work in process inventory.

No definition available.

Name:	mcp_CapitalizationOfDepletionCostsInWIPInventory
Namespace Prefix:	mcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration