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Share Based Compensation Service Based Awards Rollforward (Details) (Service-Based Share Awards [Member])
12 Months Ended
Dec. 31, 2014
Service-Based Share Awards [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Service-based share awards outstanding, beginning of period (in Shares) 442,737us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= cenx_ServiceBasedShareAwardsMember
Granted (in Shares) 258,662us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= cenx_ServiceBasedShareAwardsMember
Vested (in Shares) (200,965)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
/ us-gaap_AwardTypeAxis
= cenx_ServiceBasedShareAwardsMember
Forfeited (in Shares) (35,949)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
/ us-gaap_AwardTypeAxis
= cenx_ServiceBasedShareAwardsMember
Service-based share awards outstanding, end of period (in Shares) 464,485us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= cenx_ServiceBasedShareAwardsMember