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Components of Accumulated other comprehensive loss (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014	Dec. 31, 2014		Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	$ (129,452)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1			$ (129,913)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1
Income tax effect	11,848cenx_AccumulatedOtherComprehensiveIncomeTaxEffect	[1]		12,231cenx_AccumulatedOtherComprehensiveIncomeTaxEffect	[1]
Accumulated other comprehensive loss	(117,604)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax		(91,733)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax	(117,682)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax		(91,832)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
Other comprehensive income (loss) before reclassifications			(17)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax
Net amount reclassified to net income (loss)	78us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax		116us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax
Cost of goods sold	493,816us-gaap_CostOfGoodsSold		422,605us-gaap_CostOfGoodsSold
Selling, general and administrative expenses	11,971us-gaap_SellingGeneralAndAdministrativeExpense		10,062us-gaap_SellingGeneralAndAdministrativeExpense
Income tax benefit (expense)	9,301us-gaap_IncomeTaxExpenseBenefit		(1,094)us-gaap_IncomeTaxExpenseBenefit
Net of tax	73,779us-gaap_NetIncomeLoss		(20,104)us-gaap_NetIncomeLoss
Defined benefit plans liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive loss before income tax effect	(128,156)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember			(128,664)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Income tax effect	12,421cenx_AccumulatedOtherComprehensiveIncomeTaxEffect / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember			12,812cenx_AccumulatedOtherComprehensiveIncomeTaxEffect / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Accumulated other comprehensive loss	(115,735)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		(77,766)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember	(115,852)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		(77,921)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Other comprehensive income (loss) before reclassifications			0us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Net amount reclassified to net income (loss)	117us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		155us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Equity in investee other comprehensive income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	0us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = cenx_AccumulatedEquityInInvesteeAdjustmentMember		(12,249)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = cenx_AccumulatedEquityInInvesteeAdjustmentMember	0us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = cenx_AccumulatedEquityInInvesteeAdjustmentMember		(12,232)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = cenx_AccumulatedEquityInInvesteeAdjustmentMember
Other comprehensive income (loss) before reclassifications			(17)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax / us-gaap_StatementEquityComponentsAxis = cenx_AccumulatedEquityInInvesteeAdjustmentMember
Net amount reclassified to net income (loss)	0us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax / us-gaap_StatementEquityComponentsAxis = cenx_AccumulatedEquityInInvesteeAdjustmentMember		0us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax / 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	(1,296)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember			(1,249)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember
Income tax effect	(573)cenx_AccumulatedOtherComprehensiveIncomeTaxEffect / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember			(581)cenx_AccumulatedOtherComprehensiveIncomeTaxEffect / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember
Accumulated other comprehensive loss	(1,869)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		(1,718)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember	(1,830)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		(1,679)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember
Other comprehensive income (loss) before reclassifications			0us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember
Net amount reclassified to net income (loss)	(39)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		(39)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember
Reclassification out of Accumulated Other Comprehensive Income [Member] | Defined benefit plans liabilities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold	325us-gaap_CostOfGoodsSold / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		590us-gaap_CostOfGoodsSold / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Selling, general and administrative expenses	183us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		268us-gaap_SellingGeneralAndAdministrativeExpense / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Income tax benefit (expense)	(391)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		(703)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Net of tax	117us-gaap_NetIncomeLoss / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember		155us-gaap_NetIncomeLoss / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember
Reclassification out of Accumulated Other Comprehensive Income [Member] | Equity in investee other comprehensive income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax benefit (expense)	0us-gaap_IncomeTaxExpenseBenefit / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = cenx_AccumulatedEquityInInvesteeAdjustmentMember		(17)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = cenx_AccumulatedEquityInInvesteeAdjustmentMember
Net of tax	0us-gaap_NetIncomeLoss / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = cenx_AccumulatedEquityInInvesteeAdjustmentMember		(17)us-gaap_NetIncomeLoss / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = cenx_AccumulatedEquityInInvesteeAdjustmentMember
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized loss on financial instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cost of goods sold	(47)us-gaap_CostOfGoodsSold / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		(47)us-gaap_CostOfGoodsSold / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember
Income tax benefit (expense)	8us-gaap_IncomeTaxExpenseBenefit / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		8us-gaap_IncomeTaxExpenseBenefit / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember
Net of tax	$ (39)us-gaap_NetIncomeLoss / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember		$ (39)us-gaap_NetIncomeLoss / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember
[1] The allocation of the income tax effect to the components of other comprehensive income is as follows: March 31, 2015December 31, 2014Defined benefit plan liabilities$12,421$12,812Unrealized loss on financial instruments(573)(581)

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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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Total costs related to goods produced and sold during the reporting period.

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