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Asset retirement obligations (“ARO”) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Asset Retirement Obligation [Roll Forward]
Beginning balance, ARO liability	$ 36,950us-gaap_AssetRetirementObligation	$ 27,113us-gaap_AssetRetirementObligation
Additional ARO liability incurred	1,476us-gaap_AssetRetirementObligationLiabilitiesIncurred	2,548us-gaap_AssetRetirementObligationLiabilitiesIncurred
ARO liabilities settled	(1,298)us-gaap_AssetRetirementObligationLiabilitiesSettled	(4,731)us-gaap_AssetRetirementObligationLiabilitiesSettled
Accretion expense	74us-gaap_AssetRetirementObligationAccretionExpense	1,517us-gaap_AssetRetirementObligationAccretionExpense
ARO liability from Mt. Holly acquisition	0cenx_BusinessAcquisitionPurchasePriceAllocationAssetRetirementObligation	10,503cenx_BusinessAcquisitionPurchasePriceAllocationAssetRetirementObligation
Ending balance, ARO liability	$ 37,202us-gaap_AssetRetirementObligation	$ 36,950us-gaap_AssetRetirementObligation

X

- Definition

The amount of acquisition cost of a business combination allocated to asset retirement obligation of the acquired entity.

+ References

No definition available.

+ Details

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

X

- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849



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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Asset Retirement Obligation

-URI http://asc.fasb.org/extlink&oid=6505190

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount of asset retirement obligations incurred during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

+ Details

Name:	us-gaap_AssetRetirementObligationLiabilitiesIncurred
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

+ Details

Name:	us-gaap_AssetRetirementObligationLiabilitiesSettled
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

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