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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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The percentage of ownership in property, plant and equipment of partnership.

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A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

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-Publisher SEC

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Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date before deducting unamortized discount or premiums (if any). May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer.

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Interest rate stated in the contractual debt agreement.

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Date when the debt instrument is scheduled to be fully repaid, which may be presented in a variety of ways (year, month and year, day, month and year, quarter, etc.).

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Aggregate amount of intangible asset amortization recognized as expense during the period.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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The maximum useful life of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

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