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Related Party Transactions (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Summary of related party transactions [Abstract] |  |  |
Net sales to Glencore | $ 564,431 | $ 413,408 | $ 230,909
Glencore International AG [Member] |  |  |
Purchases from Glencore [Abstract] |  |  |
Overall alumina supply reduction (in metric tons) |  | 280,000 |
Amount of alumina to be supplied For Grundartangi at a fixed price (in metric tons) |  | 18,000 |
Other Transactions with related party [Abstract] |  |  |
Noncontrolling ownership percentage by Glencore International AG, a previous owner of company (in hundredths) | 41.60% |  |
Percentage of beneficial ownership through common and preferred stock (in hundredths) | 46.40% |  |
Summary of related party transactions [Abstract] |  |  |
Net sales to Glencore | 564,431 | 413,408 | 230,909
Cash premium to Glencore for put option contracts | 2,106 | 6,341 | 7,228
Purchases from Glencore | 187,691 | 106,381 | 37,683
Glencore's participation in common stock offerings | 0 | 0 | 59,590
BHH [Member] |  |  |
Summary of related party transactions [Abstract] |  |  |
Purchases from BHH | $ 19,543 | $ 19,690 | $ 15,218
Noncontrolling ownership percentage in related party (in hundredths) | 40.00% |  |

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