Related Party Transaction, Sales Agreement, Amount

No definition available.

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- Definition

This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 35
-Paragraph 32
-URI http://asc.fasb.org/extlink&oid=64825282&loc=d3e32787-111569

+ Details

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

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

+ Details

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

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=cenx_GlencoreMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=cenx_BhhMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_RelatedPartyTransactionAxis=cenx_AgreementtoSellMoltenAluminumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_AffiliatedEntityMember
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Data Type:	na
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- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockMember
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Data Type:	na
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Related party transactions - Narrative (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Dec. 31, 2015 USD ($)	Jun. 30, 2016 t
Glencore [Member]
Related Party Transaction [Line Items]
Ownership percentage by majority shareholder		47.50%
BHH [Member]
Related Party Transaction [Line Items]
Ownership percentage		40.00%
Impairment of equity method investment \| $	$ 11,584
Agreement to Sell Molten Aluminum [Member] \| Affiliated Entity [Member]
Related Party Transaction [Line Items]
Sales agreement, amount of agreement (tonnes) \| t		24,500
Common Stock [Member] \| Glencore [Member]
Related Party Transaction [Line Items]
Ownership percentage by majority shareholder		42.90%