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Quarterly information (Unaudited) - 2015 Financial Results Overview (Details) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2015 | Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Effect of Fourth Quarter Events [Line Items] |  |  |  |  |  |  |  |  |
Lower cost or market inventory adjustment |  | $ 23,474 | $ 5,324 |  |  |  | $ 7,539 | $ (1,247) | $ 1,247
Pension charges |  | 3,400 |  |  |  | $ 4,964 |  |  |
Depreciation |  |  |  |  |  |  | 80,117 | 70,827 | 66,570
Impairment |  |  |  |  |  |  | 11,584 | 0 | 0
Labor disruption costs |  |  | 1,400 | $ 11,700 |  |  |  |  |
Impairment charge |  |  |  |  |  |  | 30,850 | 0 | 0
Gain on fair value of contingent consideration |  |  |  |  | $ 6,527 | $ 7,943 | 18,337 | $ 7,943 | $ 0
Severance charge |  |  |  |  | 1,000 |  |  |  |
Hawesville and Mt. Holly [Member] |  |  |  |  |  |  |  |  |
Effect of Fourth Quarter Events [Line Items] |  |  |  |  |  |  |  |  |
Curtailment expenses |  | 3,500 |  |  |  |  |  |  |
Hawesville [Member] |  |  |  |  |  |  |  |  |
Effect of Fourth Quarter Events [Line Items] |  |  |  |  |  |  |  |  |
Curtailment expenses |  |  | $ 2,900 |  |  |  |  |  |
Ravenswood Aluminum Smelter [Member] |  |  |  |  |  |  |  |  |
Effect of Fourth Quarter Events [Line Items] |  |  |  |  |  |  |  |  |
Lower cost or market inventory adjustment |  |  |  | 25,689 |  |  |  |  |
Impairment charge | $ 30,850 |  |  | 30,850 |  |  |  |  |
Grundartangi, Iceland [Member] |  |  |  |  |  |  |  |  |
Effect of Fourth Quarter Events [Line Items] |  |  |  |  |  |  |  |  |
Signing bonuses, amount |  |  |  |  | $ 1,570 |  |  |  |
Mt. Holly Smelter [Member] |  |  |  |  |  |  |  |  |
Effect of Fourth Quarter Events [Line Items] |  |  |  |  |  |  |  |  |
Depreciation |  | 5,000 |  |  |  |  |  |  |
Gain on fair value of contingent consideration |  |  |  | $ 10,287 |  |  | 18,337 |  |
BHH [Member] |  |  |  |  |  |  |  |  |
Effect of Fourth Quarter Events [Line Items] |  |  |  |  |  |  |  |  |
Impairment |  | $ 11,584 |  |  |  |  | $ 11,584 |  |

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