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Commitments and contingencies (Details) (USD $) In Thousands, unless otherwise specified	165 Months Ended	3 Months Ended	12 Months Ended	45 Months Ended
	Mar. 31, 2015 LaborUnions	Mar. 31, 2015	Dec. 31, 2013	Dec. 31, 2016	Dec. 31, 2014	Dec. 31, 2011 MW
Environmental Contingencies [Abstract]
Environmental-related accrued liabilities	$ 1,209us-gaap_AccrualForEnvironmentalLossContingencies	$ 1,209us-gaap_AccrualForEnvironmentalLossContingencies			$ 1,101us-gaap_AccrualForEnvironmentalLossContingencies
Environmental remediation expense for Hydrocarbon Recovery Plan	1,033us-gaap_EnvironmentalRemediationExpense
OR Power Agreement [Abstract]
Power currently available under the power purchase agreement (in megawatts)						47.5cenx_PowerAvailable
Power prepayments	2,022us-gaap_PrepaidExpenseNoncurrent	2,022us-gaap_PrepaidExpenseNoncurrent
Labor Commitments [Abstract]
Percentage of total work force in union (in hundredths)	59.00%cenx_PercentageofWorkForceinUnion	59.00%cenx_PercentageofWorkForceinUnion
Percentage of U.S. based work force represented by a union (in hundredths)	54.00%cenx_PercentageOfDomesticWorkForceInUnion	54.00%cenx_PercentageOfDomesticWorkForceInUnion
Number of labor unions Grundartangi subsidiary entered into a new labor agreement with	5cenx_NumberOfLaborUnionsUnderNewLaborAgreement	5cenx_NumberOfLaborUnionsUnderNewLaborAgreement
Percentage of Grundartangi work force represented by the labor unions (in hundredths)	81.00%cenx_PercentageOfForeignWorkForceCoveredUnderNewLaborAgreement	81.00%cenx_PercentageOfForeignWorkForceCoveredUnderNewLaborAgreement
Percentage of Vlissingen work force represented by the labor union (in hundredths)	80.00%cenx_PercentageofforeignNetherlandsworkforcerepresentedbythelaborunioninhundredths	80.00%cenx_PercentageofforeignNetherlandsworkforcerepresentedbythelaborunioninhundredths
PBGC Agreement [Member]
PBCG Settlement [Abstract]
Pension contributions		1,076us-gaap_PensionContributions / us-gaap_LossContingenciesByNatureOfContingencyAxis = cenx_PBGCAgreementMember	6,700us-gaap_PensionContributions / us-gaap_LossContingenciesByNatureOfContingencyAxis = cenx_PBGCAgreementMember
PBGC Forecast [Member] | PBGC Agreement [Member]
PBCG Settlement [Abstract]
Pension contributions above required minimum, total				$ 17,400cenx_PensionContributionsAboveRequiredMinimumTotal / us-gaap_LossContingenciesByNatureOfContingencyAxis = cenx_PBGCAgreementMember / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember

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The number of labor unions representing a group of employees.

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Pursuant to the terms of the settlement agreement with the Pension Benefit Guaranty Corporation, we will make additional contributions (above any minimum required contributions) to our defined benefit pension plans.

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The percentage of a Company's work force, based in the country of domicile, that are subject to collective bargaining agreements.

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No definition available.

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The percentage of a Company's Netherlands work force that are subject to collective bargaining agreements

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- Definition

The percentage of a Company's Icelandic work force that are subject to collective bargaining agreements.

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The power currently available under the power purchase agreement.

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities.

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The amount of cash or cash equivalents contributed by the entity to fund its pension plans.

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Sum of the carrying amounts as of the balance sheet date of amounts paid in advance for expenses which will be charged against earnings in periods after one year or beyond the operating cycle, if longer.

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