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Forward delivery contracts and financial instruments (Details)
 12 Months Ended
Dec. 31, 2014
t
Dec. 31, 2013
t
Long-Term Tolling Contracts [Member] | Glencore Toll Agreement 1 [Member]    
Supply Commitment [Line Items]    
Annual Primary Aluminum Physical Delivery Contract_Maximum 90,000cenx_AnnualPrimaryAluminumPhysicalDeliveryContract_Maximum
/ cenx_NameOfContractAxis
= cenx_GlencoreTollAgreement1Member
/ us-gaap_SupplyCommitmentAxis
= cenx_LongTermTollingContractsMember		  
Customer Glencore  
Volume 90,000 tonnes per year ("tpy")  
Term Through July 2016  
Pricing Variable, based on LME and European Duty Paid premium  
Primary Aluminum Sales Contracts [Member] | Glencore Nordural Metal Agreement [Member]    
Supply Commitment [Line Items]    
Annual Primary Aluminum Physical Delivery Contract_Maximum 205,000cenx_AnnualPrimaryAluminumPhysicalDeliveryContract_Maximum
/ cenx_NameOfContractAxis
= cenx_GlencoreNorduralMetalAgreementMember
/ us-gaap_SupplyCommitmentAxis
= cenx_PrimaryAluminumSalesContractsMember		  
Customer Glencore [1]  
Volume All primary aluminum produced at Grundartangi, net of tolling and other sales commitments [1]  
Term January 1, 2014 through December 31, 2017 [1]  
Pricing Variable, based on LME and European Duty Paid premium and product premiums, as applicable [1]  
Other Forward Delivery Contracts [Member]    
Supply Commitment [Line Items]    
Other forward delivery contracts to sell primary aluminum (in tonnes) 6,108cenx_OtherPrimaryAluminumDeliveryCommitmentsAndContractsVolume
/ us-gaap_SupplyCommitmentAxis
= us-gaap_ForwardContractsMember		 118,373cenx_OtherPrimaryAluminumDeliveryCommitmentsAndContractsVolume
/ us-gaap_SupplyCommitmentAxis
= us-gaap_ForwardContractsMember
Glencore [Member] | Other Forward Delivery Contracts [Member]    
Supply Commitment [Line Items]    
Other forward delivery contracts to sell primary aluminum (in tonnes) 4,058cenx_OtherPrimaryAluminumDeliveryCommitmentsAndContractsVolume
/ dei_LegalEntityAxis
= cenx_GlencoreMember
/ us-gaap_SupplyCommitmentAxis
= us-gaap_ForwardContractsMember		 20,008cenx_OtherPrimaryAluminumDeliveryCommitmentsAndContractsVolume
/ dei_LegalEntityAxis
= cenx_GlencoreMember
/ us-gaap_SupplyCommitmentAxis
= us-gaap_ForwardContractsMember
[1] The Glencore Grundartangi Metal Agreement is for all metal produced at Grundartangi from 2014 through 2017 less commitments under existing tolling and other sales contracts. Grundartangi currently estimates that it will sell Glencore approximately 205,000 tonnes of aluminum under this agreement in 2015.