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Commitments and contingencies (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	156 Months Ended			15 Months Ended	45 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2014	Dec. 31, 2013	Dec. 31, 2011 MW	Jun. 30, 2014 PBGC Agreement [Member]	Dec. 31, 2016 PBGC Forecast [Member] PBGC Agreement [Member]	Jun. 30, 2014 St. Croix Alumina Refinery [Member]	Apr. 30, 2013 Grundartangi Power Agreement [Member]	Jun. 30, 2014 Grundartangi OR Power Agreement [Member]
Environmental Contingencies [Abstract]
Environmental-related accrued liabilities	$ 1,228	$ 1,228	$ 999
Environmental remediation expense minimum amount entitling reimbursement by third party	400
Environmental remediation expense for Hydrocarbon Recovery Plan		1,033
Legal Contingencies [Abstract]
Legal settlement award payment							625	1,470	3,600
PBCG Settlement [Abstract]
Pension contributions above required minimum, total						17,400
Pension contributions					6,700
OR Power Agreement [Abstract]
Power currently available under the power purchase agreement (in megawatts)				47.5
Power prepayments	$ 2,000	$ 2,000
Labor Commitments [Abstract]
Percentage of U.S. based work force represented by a union (in hundredths)	73.00%	73.00%
Number of labor unions Grundartangi subsidiary entered into a new labor agreement with	5	5
Percentage of Grundartangi work force represented by the labor unions (in hundredths)	82.00%	82.00%
Percentage of Vlissingen work force represented by the labor union (in hundredths)	77.00%	77.00%

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The minimum amount of environmental remediation expenses that must occur before entitlement to third party reimbursement.

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The number of labor unions representing a group of employees.

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Pursuant to the terms of the settlement agreement with the Pension Benefit Guaranty Corporation, we will make additional contributions (above any minimum required contributions) to our defined benefit pension plans.

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The percentage of a Company's work force, based in the country of domicile, that are subject to collective bargaining agreements.

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The percentage of a Company's Netherlands work force that are subject to collective bargaining agreements

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The percentage of a Company's Icelandic work force that are subject to collective bargaining agreements.

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The power currently available under the power purchase agreement.

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities.

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Amount of judgment or settlement awarded to (against) the entity in respect of litigation.

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The amount of cash or cash equivalents contributed by the entity to fund its pension plans.

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Sum of the carrying amounts as of the balance sheet date of amounts paid in advance for expenses which will be charged against earnings in periods after one year or beyond the operating cycle, if longer.

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