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v3.3.1.900

Summary of significant accounting policies (Details) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2015 | Dec. 31, 2015 | Jun. 30, 2015 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Glencore beneficial ownership |  | 42.90% |  | 42.90% |  |
Glencore economic ownership |  | 47.50% |  | 47.50% |  |
Allowance for doubtful accounts receivable |  | $ 1,000 |  | $ 1,000 | $ 1,000 |
BHH impairment |  |  |  | 11,584 | 0 | $ 0
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Impairment charge |  |  |  | $ 30,850 | $ 0 | $ 0
Ravenswood Aluminum Smelter [Member] |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Impairment charge | $ 30,850 |  | $ 30,850 |  |  |
Minimum [Member] | Building and Improvements [Member] |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Useful life |  |  |  | 10 years |  |
Minimum [Member] | Machinery and Equipment [Member] |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Useful life |  |  |  | 5 years |  |
Minimum [Member] | Technology and Software [Member] |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Useful life |  |  |  | 3 years |  |
Maximum [Member] | Building and Improvements [Member] |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Useful life |  |  |  | 45 years |  |
Maximum [Member] | Machinery and Equipment [Member] |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Useful life |  |  |  | 35 years |  |
Maximum [Member] | Technology and Software [Member] |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Useful life |  |  |  | 7 years |  |
Baise Haohi Carbon Co Ltd [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage, equity method |  | 40.00% |  | 40.00% |  |
BHH [Member] |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |
Ownership percentage, equity method |  | 40.00% |  | 40.00% |  |
BHH impairment |  | $ 11,584 |  | $ 11,584 |  |

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