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Debt E.ON contingent obligation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Unrealized gain (loss) on E.ON obligation	$ 15,722cenx_UnrealizedGainLossOnEOnObligation	$ 1,412cenx_UnrealizedGainLossOnEOnObligation	$ 16,781cenx_UnrealizedGainLossOnEOnObligation	$ 0cenx_UnrealizedGainLossOnEOnObligation
E.ON Contingent Obligation		0cenx_EOnContingentObligation	0cenx_EOnContingentObligation
Long-term Debt [Member] | Contingent obligation [Member]
Debt Instrument [Line Items]
Payment terms		72 monthly payments
Unrealized gain (loss) on E.ON obligation		1,412cenx_UnrealizedGainLossOnEOnObligation / us-gaap_DebtInstrumentAxis = cenx_ContingentObligationMember / us-gaap_LongtermDebtTypeAxis = us-gaap_LongTermDebtMember	16,781cenx_UnrealizedGainLossOnEOnObligation / us-gaap_DebtInstrumentAxis = cenx_ContingentObligationMember / us-gaap_LongtermDebtTypeAxis = us-gaap_LongTermDebtMember
Debt Instrument, Interest Rate, Stated Percentage		10.94%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_DebtInstrumentAxis = cenx_ContingentObligationMember / us-gaap_LongtermDebtTypeAxis = us-gaap_LongTermDebtMember
Other Liabilities [Member] | Contingent obligation [Member]
Debt Instrument [Line Items]
E.ON contingent obligation – principal		(12,902)cenx_E.ONContingentObligationPrincipal / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherLiabilitiesMember / us-gaap_DebtInstrumentAxis = cenx_ContingentObligationMember	(12,902)cenx_E.ONContingentObligationPrincipal / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherLiabilitiesMember / us-gaap_DebtInstrumentAxis = cenx_ContingentObligationMember
E.ON contingent obligation – accrued interest		(5,291)cenx_E.ONContingentObligationAccruedInterest / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherLiabilitiesMember / us-gaap_DebtInstrumentAxis = cenx_ContingentObligationMember	(3,879)cenx_E.ONContingentObligationAccruedInterest / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherLiabilitiesMember / us-gaap_DebtInstrumentAxis = cenx_ContingentObligationMember
E.ON contingent obligation – derivative asset		18,193cenx_E.ONContingentObligationDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherLiabilitiesMember / us-gaap_DebtInstrumentAxis = cenx_ContingentObligationMember	16,781cenx_E.ONContingentObligationDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherLiabilitiesMember / us-gaap_DebtInstrumentAxis = cenx_ContingentObligationMember
E.ON Contingent Obligation		$ 0cenx_EOnContingentObligation / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherLiabilitiesMember / us-gaap_DebtInstrumentAxis = cenx_ContingentObligationMember	$ 0cenx_EOnContingentObligation / us-gaap_BalanceSheetLocationAxis = us-gaap_OtherLiabilitiesMember / us-gaap_DebtInstrumentAxis = cenx_ContingentObligationMember

X

- Definition

This amount represents the accrued interest on the E.ON contingent obligation, which is defined as the sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

+ References

No definition available.

+ Details

Name:	cenx_E.ONContingentObligationAccruedInterest
Namespace Prefix:	cenx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

This amount represents the derivative asset recorded for the E.ON contingent obligation, which is defined as the sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

This amount represents the principal amount of the E.ON contingent obligation, which is defined as the sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

+ References

No definition available.

+ Details

Name:	cenx_E.ONContingentObligationPrincipal
Namespace Prefix:	cenx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

+ References

No definition available.

+ Details

Name:	cenx_EOnContingentObligation
Namespace Prefix:	cenx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The net change in the difference between the fair value and the carrying value on the contingent obligation held at each balance sheet date, that was included in earnings for the period.

+ References

No definition available.

+ Details

Name:	cenx_UnrealizedGainLossOnEOnObligation
Namespace Prefix:	cenx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Description of the payment terms of the debt instrument (for example, whether periodic payments include principal and frequency of payments) and discussion about any contingencies associated with the payment.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(3))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Period Type:	duration

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- Details

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X

- Details

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Period Type: