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Summary of significant accounting policies (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended |  |  |  | 12 Months Ended |  | 12 Months Ended |  | 12 Months Ended |  | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2009 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2011 Berkeley Aluminum [Member] Partnership Aluminum Reduction Facility 2010 [Member] | Dec. 31, 2011 Berkeley Aluminum [Member] Property, Plant and Equipment Owned By Partnership [Member] | Dec. 31, 2011 Century Aluminum Company [Member] Baise Haohi Carbon Co Ltd [Member] | Dec. 31, 2011 Glencore International AG [Member] | Dec. 31, 2011 Senior secured notes due May 15, 2014 [Member] | Dec. 31, 2010 Senior secured notes due May 15, 2014 [Member] | Dec. 31, 2011 Senior unsecured notes due August 15, 2014 [Member] | Dec. 31, 2010 Senior unsecured notes due August 15, 2014 [Member] | Dec. 31, 2011 Convertible senior notes due 2024 [Member] | Dec. 31, 2010 Convertible senior notes due 2024 [Member] | Dec. 31, 2011 Building and Building Improvements [Member] | Dec. 31, 2011 Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated useful life minimum (in years) |  |  |  |  |  |  |  |  |  |  |  |  |  | 14 | 5
Estimated useful life maximum (in years) |  |  |  |  |  |  |  |  |  |  |  |  |  | 45 | 22
Financial Instruments - debt [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Carrying amount |  |  |  |  |  |  |  | $ 246,909 | $ 245,927 | $ 2,603 | $ 2,603 | $ 0 | $ 45,483 |  |
Fair value |  |  |  |  |  |  |  | 249,292 | 249,604 | 2,564 | 2,541 | 0 | 46,588 |  |
Maturity date |  |  |  |  |  |  |  | May 15, 2014 |  | Aug. 15, 2014 |  | Aug. 31, 2024 |  |  |
Interest rate (in hundredths) |  |  |  |  |  |  |  | 8.00% |  | 7.50% |  | 1.75% |  |  |
Organization and basis of presentation [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Equity ownership interest in entity (in hundredths) |  |  |  | 49.70% |  | 40.00% |  |  |  |  |  |  |  |  |
Equity ownership interest in physical assets of partnership (in hundredths) |  |  |  |  | 49.70% |  |  |  |  |  |  |  |  |  |
Noncontrolling ownership percentage by Glencore International AG, a previous owner of company (in hundredths) |  |  |  |  |  |  | 41.60% |  |  |  |  |  |  |  |
Accounts receivable [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Allowance for uncollectible accounts |  | 734 | 734 |  |  |  |  |  |  |  |  |  |  |  |
Goodwill [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortization expense for the intangible asset | $ 8,769 |  |  |  |  |  |  |  |  |  |  |  |  |  |

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