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

X

- 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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X

- 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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X

- 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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X

- 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

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