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%

Cash premium paid to glencore for put option contracts.

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The percentage of common stock and preferred stock of the company owned by a related party.

+ References

No definition available.

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- Definition

The metric tons of alumina to be supplied at a fixed rate.

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No definition available.

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- Definition

The over all reduction in the metric tons of alumina to be supplied due to amendments.

+ References

No definition available.

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The cash inflow from the additional capital contribution to the entity received from related parties.

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No definition available.

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- Definition

Direct costs arising from transactions with related parties who are not affiliates or joint Ventures. These costs are categorized as cost of goods sold.

+ References

No definition available.

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- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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No definition available.

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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Direct costs arising from transactions with related parties who are not affiliates or joint Ventures. These costs are categorized as cost of goods sold.

+ References

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Revenues arising from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, such as pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's' management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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