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Commitments and Contingencies (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009 | Dec. 31, 2006
Environmental Contingencies [Abstract] |  |  |  |
Aggregate environmental-related accrued liabilities | $ 852 | $ 753 |  |
Number of violations relating to the Clean Air Act | 2 |  | 12 |
Fine paid in settlement of violations relating to the Clean Air Act | 178 |  |  |
Number of sites in which interim remediation measures have been completed | 2 |  |  |
Minimum amount expended by Company entitling them to reimbursement by third party for operating and maintaining water treatment system on behalf of third party | 400 |  |  |
Amount expended on hydrocarbon recovery plan under EPA Administrative Order | 840 |  |  |
Expected future potential payments under indemnification plan in order to comply with EPA Administrative Order | 500 |  |  |
Number of succeeding owners of alumina facility named as defendants in a lawsuit filed by the Commissioner of the Department of Planning and Natural Resources |  |  |  | 2
Number of plaintiffs to lawsuit alleging violations of territorial water pollution control laws in first lawsuit |  | 2,300 |  |
Number of plaintiffs to lawsuit alleging violations of territorial water pollution control laws in second lawsuit | 200 |  |  |
Damages sought for breach of contract and wrongful termination | $ 20,000 |  |  |
Ravenswood Retiree Medical Benefits [Abstract] |  |  |  |
Age at which retiree medical benefits will cease for retirees and dependents (age in years) | 65Y |  |  |
Age at which bargaining unit retirees and qualified dependents are covered by the salary retiree medical plan (age in years) | under 65Y |  |  |
Number of retirees in part of class action lawsuit regarding Company's rights to modify or terminate retiree medical benefits |  |  | 4 |
Helguvik Agreement [Abstract] |  |  |  |
Power currently available under the power purchase agreement (in megawatts) | 47.5 |  |  |
Labor Commitments [Abstract] |  |  |  |
Percentage of U.S. based work force represented by a union (in hundredths) | 75.00% |  |  |
Number of labor unions foreign subsidiary entered into a new labor agreement with |  | 5 |  |
Percentage of foreign work force represented by the labor unions (in hundredths) |  | 84.00% |  |

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