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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%