Derivatives (Details) $ in Thousands	3 Months Ended
Mar. 31, 2017 USD ($) MWh t	Mar. 31, 2016 USD ($)
Derivative [Line Items]
Derivative asset \| $	$ 1,610
Derivative liability \| $	14,915
Recognized loss on derivative instruments \| $	$ 16,137	$ (353)
LME Swap [Member]
Derivative [Line Items]
Other forward delivery contracts to sell primary aluminum (in tonnes)	52,590
Other forward delivery contracts to sell primary aluminum, settled monthly (in tonnes)	49,500
Price Swap [Member]
Derivative [Line Items]
Open position to offset fixed prices	7,931
Affiliated Entity [Member] \| LME Swap [Member]
Derivative [Line Items]
Other forward delivery contracts to sell primary aluminum (in tonnes)	48,540
Grundartangi [Member] \| Power Price Swap [Member]
Derivative [Line Items]
Percentage of power purchases included in forward price contract (percent)	4.00%
Power available \| MWh	256,200

Derivative, Financial Contract, Percentage

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- Definition

Total amount of primary aluminum committed to be supplied under existing contracts or agreements outside of major long-term supply commitments.

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Other Primary Aluminum Delivery Commitments And Contracts Volume, Monthly Settlement Amount

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- Definition

The power currently available under the power purchase agreement.

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No definition available.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Nominal mass used to calculate payments on a derivative instrument.

+ References

No definition available.

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- Definition

Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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