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Derivative and hedging instruments Part 2 (Details) (Not Designated as Hedging Instrument [Member], USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
E.ON Contingent Obligation [Member] | Net Gain (Loss) on Forward and Derivative Contracts [Member] |  |
Derivatives not designated as hedging instruments [Abstract] |  |
Gain (loss) recognized in income from derivatives | $ 1,412 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = cenx_EOnContingentObligationMember / us-gaap_HedgingDesignationAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = cenx_NetGainLossOnForwardContractsMember | $ 16,781 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = cenx_EOnContingentObligationMember / us-gaap_HedgingDesignationAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = cenx_NetGainLossOnForwardContractsMember
E.ON Contingent Obligation [Member] | Interest Expense [Member] |  |
Derivatives not designated as hedging instruments [Abstract] |  |
Gain (loss) recognized in income from derivatives | (1,412)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = cenx_EOnContingentObligationMember / us-gaap_HedgingDesignationAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = us-gaap_InterestExpenseMember | (1,412)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = cenx_EOnContingentObligationMember / us-gaap_HedgingDesignationAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = us-gaap_InterestExpenseMember
Midwest Premium Contracts [Member] | Net Gain (Loss) on Forward and Derivative Contracts [Member] |  |
Derivatives not designated as hedging instruments [Abstract] |  |
Gain (loss) recognized in income from derivatives | (1,080)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = cenx_MidwestPremiumContractsMember / us-gaap_HedgingDesignationAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = cenx_NetGainLossOnForwardContractsMember | 140 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = cenx_MidwestPremiumContractsMember / us-gaap_HedgingDesignationAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = cenx_NetGainLossOnForwardContractsMember
Primary Aluminum Sales Contracts [Member] | Net Gain (Loss) on Forward and Derivative Contracts [Member] |  |
Derivatives not designated as hedging instruments [Abstract] |  |
Gain (loss) recognized in income from derivatives | (153)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = cenx_PrimaryAluminumSalesContractsMember / us-gaap_HedgingDesignationAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = cenx_NetGainLossOnForwardContractsMember | (323)us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = cenx_PrimaryAluminumSalesContractsMember / us-gaap_HedgingDesignationAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = cenx_NetGainLossOnForwardContractsMember
Primary Aluminum Sales Contracts [Member] | Related Party Sales [Member] |  |
Derivatives not designated as hedging instruments [Abstract] |  |
Gain (loss) recognized in income from derivatives | $ 292 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = cenx_PrimaryAluminumSalesContractsMember / us-gaap_HedgingDesignationAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = cenx_RelatedPartySalesMember | $ 1,353 us-gaap_DerivativeGainLossOnDerivativeNet / us-gaap_DerivativeInstrumentRiskAxis = cenx_PrimaryAluminumSalesContractsMember / us-gaap_HedgingDesignationAxis = us-gaap_NondesignatedMember / us-gaap_IncomeStatementLocationAxis = cenx_RelatedPartySalesMember

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624171-113959 + Details
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- Details
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