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Supplemental financial statement info Components of Accumulated Other Comprehensive Loss (Details) (USD $)
In Thousands, unless otherwise specified

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Accumulated Other Comprehensive Income (Loss) [Line Items]

Other comprehensive loss before income tax effect

$ (129,913)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1

$ (105,891)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1

Income tax effect (2)

12,231cenx_AccumulatedOtherComprehensiveIncomeTaxEffect

^[1]

14,059cenx_AccumulatedOtherComprehensiveIncomeTaxEffect

^[1]

Accumulated other comprehensive loss

(117,682)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax

(91,832)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax

(151,192)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax

(134,588)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax

Defined benefit plan liabilities [Member]

Accumulated Other Comprehensive Income (Loss) [Line Items]

Other comprehensive loss before income tax effect

(128,664)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember

(92,177)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember

Income tax effect (2)

12,812cenx_AccumulatedOtherComprehensiveIncomeTaxEffect
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember

14,256cenx_AccumulatedOtherComprehensiveIncomeTaxEffect
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember

Accumulated other comprehensive loss

(115,852)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember

(77,921)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember

(137,441)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember

(124,948)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember

Equity in investee other comprehensive income [Member]

Accumulated Other Comprehensive Income (Loss) [Line Items]

Other comprehensive loss before income tax effect

0us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1
/ us-gaap_StatementEquityComponentsAxis
= cenx_AccumulatedEquityInInvesteeAdjustmentMember

^[2]

(12,650)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1
/ us-gaap_StatementEquityComponentsAxis
= cenx_AccumulatedEquityInInvesteeAdjustmentMember

^[2]

Income tax effect (2)

0cenx_AccumulatedOtherComprehensiveIncomeTaxEffect
/ us-gaap_StatementEquityComponentsAxis
= cenx_AccumulatedEquityInInvesteeAdjustmentMember

418cenx_AccumulatedOtherComprehensiveIncomeTaxEffect
/ us-gaap_StatementEquityComponentsAxis
= cenx_AccumulatedEquityInInvesteeAdjustmentMember

Accumulated other comprehensive loss

0us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= cenx_AccumulatedEquityInInvesteeAdjustmentMember

(12,232)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= cenx_AccumulatedEquityInInvesteeAdjustmentMember

(12,224)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= cenx_AccumulatedEquityInInvesteeAdjustmentMember

(7,918)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= cenx_AccumulatedEquityInInvesteeAdjustmentMember

Unrealized loss on financial instruments [Member]

Accumulated Other Comprehensive Income (Loss) [Line Items]

Other comprehensive loss before income tax effect

(1,249)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember

(1,064)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember

Income tax effect (2)

(581)cenx_AccumulatedOtherComprehensiveIncomeTaxEffect
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember

(615)cenx_AccumulatedOtherComprehensiveIncomeTaxEffect
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember

Accumulated other comprehensive loss

$ (1,830)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember

$ (1,679)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember

$ (1,527)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember

$ (1,722)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember

[1]	The allocation of the income tax effect to the components of other comprehensive income is as follows: 20142013Defined benefit plan liabilities$12,812$14,256Equity in investee other comprehensive income—418Unrealized loss on financial instruments(581)(615)
[2]	The amount includes our equity in the other comprehensive income of Mt. Holly until it was acquired.

X

- Definition

The tax effect of AOCI as reported on the balance sheet.

+ References

No definition available.

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- Definition

Amount before tax of increase (decrease) in accumulated in equity from transactions and other events and circumstances from non-owner sources. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners (distributions to owners).

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- Definition

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 14

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e681-108580



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 14A

-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669686-108580



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 31

-Article 5



Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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