Other Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Other Assets [Line Items]
Other Assets	$ 826	$ 1,114
Other Assets,Total	25,842	2,277
Bauxite raw materials | Inventories
Other Assets [Line Items]
Inventory, Raw Materials	23,842
Bauxite raw materials | Prepayments
Other Assets [Line Items]
Inventory, Raw Materials	$ 1,174	$ 1,163