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Forward delivery contracts and financial instruments (Details) | 3 Months Ended |  |  |  |
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Mar. 31, 2013 Primary Aluminum Sales Contracts [Member] Glencore Metal Agreement [Member] t | Mar. 31, 2013 Primary Aluminum Sales Contracts [Member] Glencore Sweep Agreement [Member] | Mar. 31, 2013 Primary Aluminum Sales Contracts [Member] Glencore Nordural Metal Agreement [Member] T | Mar. 31, 2013 Primary Aluminum Sales Contracts [Member] Southwire Metal Agreement [Member] lb | Mar. 31, 2013 Long-Term Tolling Conctracts [Member] Billiton Tolling Agreement [Member] T | Mar. 31, 2013 Long-Term Tolling Conctracts [Member] Glencore Toll Agreement 1 [Member] T | Mar. 31, 2013 Long-Term Tolling Conctracts [Member] Glencore Toll Agreement 2 [Member] T | Mar. 31, 2013 Other Forward Delivery Contracts [Member] t | Dec. 31, 2012 Other Forward Delivery Contracts [Member] t | Mar. 31, 2013 Glencore [Member] Other Forward Delivery Contracts [Member] t | Dec. 31, 2012 Glencore [Member] Other Forward Delivery Contracts [Member] t
Supply Commitment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Customer | Glencore | [1] | Glencore | [2] | Glencore | Southwire | [3] | BHP Billiton | [4] | Glencore | [4] | Glencore | [4] |  |  |  |
Sales Volume Description | 20,400 mtpy | [1] | Surplus primary aluminum produced in the United States | [2] | Approximately 19,000 metric tons | 220 to 240 million pounds per year (high conductivity molten aluminum) | [3] | 130,000 mtpy | [4] | 90,000 mtpy | [4] | 40,000 mtpy | [4] |  |  |  |
Volume (in mtpy, metric tons, and pounds per year) | 20,400,000 | [1] |  |  | 19,000,000 | 240,000,000 |  | 130,000 |  | 90,000 |  | 40,000 |  |  |  |  |
Annual Primary Aluminim Physical Delivery Contract_Minimum |  |  |  |  |  | 220,000,000 |  |  |  |  |  |  |  |  |  |  |
Term | Through December 31, 2013 | [1] | Through December 31, 2013 | [2] | Through December 31, 2013 | Through December 31, 2013 | [3] | Through December 31, 2013 | [4] | Through July 31, 2016 | [4] | Through December 31, 2014 | [4] |  |  |  |
Pricing | Variable, based on U.S. Midwest market | [1] | Variable, based on U.S. Midwest market | [2] | Variable, based on LME | Variable, based on U.S. Midwest market | [3] | LME-based | [4] | LME-based | [4] | LME-based | [4] |  |  |  |
Other forward delivery contracts to sell primary aluminum (in metric tons) |  |  |  |  |  |  |  |  |  |  |  |  |  | 70,236 | 88,827 | 1,417 | 1,811
[1] | We account for the Glencore Metal Agreement as a derivative instrument under ASC 815. Under the Glencore Metal Agreement, pricing is based on then-current Midwest market prices, adjusted by a negotiated U.S. Midwest premium with a cap and a floor as applied to the current U.S. Midwest premium.
[2] | The Glencore Sweep Agreement is for all metal produced in the U.S. in 2013, less existing sales agreements and high-purity metal sales. The term of the contract may be extended for one year upon mutual agreement.
[3] | The Southwire Metal Agreement contains termination rights in the event of a partial or full curtailment of the Hawesville facility.
[4] | Grundartangi’s tolling revenues include a premium based on the European Union (“EU”) import duty for primary aluminum.

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