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Share Based Compensation Share Based Compensation (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Options to purchase common stock (in Shares)   619,833us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Service-Based Share Awards [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Service-based share awards outstanding (in Shares) 464,485us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= cenx_ServiceBasedShareAwardsMember
442,737us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= cenx_ServiceBasedShareAwardsMember
Amended and Restated Stock Option Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock Incentive Plan, shares authorized (in Shares) 10,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= cenx_AmendedandRestatedStockOptionPlanMember
 
Stock Incentive Plan, shares remaining (in Shares) 6,900,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= cenx_AmendedandRestatedStockOptionPlanMember
 
Stock Incentive Plan, expected term (years) 10 years  
Share based compensation, vesting rights (in time period) 3 years  
Options to purchase common stock (in Shares) 544,171us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= cenx_AmendedandRestatedStockOptionPlanMember
 
Amended and Restated Stock Option Plan [Member] | Non-employee director [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share based compensation, vesting rights (in time period) 12 months  
Amended and Restated Stock Option Plan [Member] | Grant date [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock Incentive Plan, vesting rights one-third  
Amended and Restated Stock Option Plan [Member] | Anniversary date [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock Incentive Plan, vesting rights one-third  
Long Term Incentive Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share based compensation, vesting rights (in time period) 3 years  
Performance unit liability 6,251us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent
/ us-gaap_PlanNameAxis
= cenx_LongTermIncentivePlanMember