Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Other Assets [Line Items]
Other Assets	$ 220	$ 826
Other Assets, Total	13,837	25,842
Bauxite raw materials | Inventories
Other Assets [Line Items]
Inventory, Raw Materials	13,143	23,842
Bauxite raw materials | Prepayments
Other Assets [Line Items]
Inventory, Raw Materials	$ 474	$ 1,174