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Derivative and hedging instruments (Details) (E.ON Contingent Obligation - Net [Member], Other Liabilities [Member], Not Designated as Hedging Instrument [Member], USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
E.ON Contingent Obligation - Net [Member] | Other Liabilities [Member] | Not Designated as Hedging Instrument [Member]
    
Fair value of derivative assets and liabilities by balance sheet location [Abstract]    
DERIVATIVE LIABILITIES $ 0us-gaap_DerivativeLiabilities
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= cenx_EOnContingentObligationMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1] $ 0us-gaap_DerivativeLiabilities
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_OtherLiabilitiesMember
/ us-gaap_DerivativeInstrumentRiskAxis
= cenx_EOnContingentObligationMember
/ us-gaap_HedgingDesignationAxis
= us-gaap_NondesignatedMember		 [1]
[1] See Note 10 Debt for additional information about the E.ON contingent obligation.