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Pension and Other Postretirement Benefits Employer contributions (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended | 45 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2016
Defined Benefit Pension Plans [Member] |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] |  |  |
Employer contributions | $ 5,584 us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | $ 11,130 us-gaap_DefinedBenefitPlanContributionsByEmployer / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |
PBGC Agreement [Member] |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] |  |  |
Pension Contributions |  | 6,700 us-gaap_PensionContributions / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cenx_PBGCAgreementMember |
Pension Contributions Above Required Minimum, Current Year Scheduled Amount | 3,700 cenx_PensionContributionsAboveRequiredMinimumCurrentYear / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cenx_PBGCAgreementMember |  |
Scenario, Forecast [Member] | PBGC Agreement [Member] |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] |  |  |
Pension Contributions Above Required Minimum, Total |  |  | 17,400 cenx_PensionContributionsAboveRequiredMinimumTotal / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cenx_PBGCAgreementMember / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember
Pension Contributions Above Required Minimum, Remaining |  |  | $ 10,700 cenx_PensionContributionsAboveRequiredMinimumRemaining / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = cenx_PBGCAgreementMember / us-gaap_StatementScenarioAxis = us-gaap_ScenarioForecastMember

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- Definition Pursuant to the terms of the settlement agreement with the Pension Benefit Guaranty Corporation, this amount represents the additional contributions (above any minimum required contributions) to our defined benefit pension plans scheduled for the current year. + References No definition available. + Details
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- Definition Pursuant to the terms of the settlement agreement with the Pension Benefit Guaranty Corporation, this amount represents the remaining additional contributions (above any minimum required contributions) to our defined benefit pension plans. + References No definition available. + Details
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- Definition 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. + References No definition available. + Details
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- Definition The increase in the fair value of plan assets from contributions made by the employer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Details
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- Definition The amount of cash or cash equivalents contributed by the entity to fund its pension plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585 + Details
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- Details
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- Details
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