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Business acquisitions Acquisition of Mt. Holly aluminum smelter (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended 12 Months Ended 0 Months Ended
Dec. 31, 2014
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 01, 2014
Business Acquisition [Line Items]          
Purchase price cash paid   $ 1,042us-gaap_PaymentsToAcquireBusinessesGross $ 48,058us-gaap_PaymentsToAcquireBusinessesGross $ 0us-gaap_PaymentsToAcquireBusinessesGross  
Gain on fair value of contingent consideration 7,943us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsRevenuesAndGainsRecognized 7,943us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsRevenuesAndGainsRecognized 0us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsRevenuesAndGainsRecognized 0us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsRevenuesAndGainsRecognized  
Gain on remeasurement of equity investment 1,318us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain 1,318us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain 0us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain 0us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain  
Contingent consideration 5,837us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent 5,837us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent 0us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent    
Pension asset (1) 30,842us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets 30,842us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets 0us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets    
Mt. Holly Smelter [Member]          
Business Acquisition [Line Items]          
Purchase price cash paid   53,831us-gaap_PaymentsToAcquireBusinessesGross
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
     
Acquisition-related costs 1,087us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
1,087us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
     
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High         22,500us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low         12,500us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Gain on fair value of contingent consideration   7,943us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsRevenuesAndGainsRecognized
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
     
Gain on remeasurement of equity investment   1,318us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
     
Purchase price         67,500cenx_BusinessAcquisitionPurchasePrice
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Pension funding (1)         46,546us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
[1]
Contingent consideration         13,780us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Economic, working capital and other closing adjustments (1)         (12,324)cenx_BusinessCombinationConsiderationReceivableOther
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
[1]
Settlement of partnership accounts         (23,172)cenx_BusinessCombinationConsiderationReceivable
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Fair value of existing equity investment         56,723us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Total consideration         149,053us-gaap_BusinessCombinationConsiderationTransferred1
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Inventories         26,105us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Due from Alumax         20,786us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Prepaid and other current assets         2,527us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Intangible asset         2,580us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Pension asset (1)         30,842us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
[1]
Property, plant and equipment – net         127,089us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Total assets acquired         209,929us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Accounts payable, trade         41,471us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Accrued and other current liabilities         8,335us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Accrued postretirement benefit costs         2,857cenx_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedPostRetirementBenefits
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
[1]
Other liabilities         8,213us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Deferred taxes         4,804us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilitiesNoncurrent
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Total liabilities assumed         65,680us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Goodwill         4,804us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
Mt. Holly revenue   25,911us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
     
Mt. Holly income from continuing operations (1)   3,024us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
[2]      
Pro forma revenues   2,176,552us-gaap_BusinessAcquisitionsProFormaRevenue
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
1,707,838us-gaap_BusinessAcquisitionsProFormaRevenue
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
   
Pro forma earnings (loss) from continuing operations   125,847us-gaap_BusinessAcquisitionsProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTax
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
(38,819)us-gaap_BusinessAcquisitionsProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTax
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
   
Pro forma earnings (loss) per common share, basic   $ 1.30us-gaap_BusinessAcquisitionProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTaxPerShareBasic
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
$ (0.44)us-gaap_BusinessAcquisitionProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTaxPerShareBasic
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
   
Pro forma earnings (loss) per common share, diluted   $ 1.29us-gaap_BusinessAcquisitionProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTaxPerShareDiluted
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
$ (0.44)us-gaap_BusinessAcquisitionProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTaxPerShareDiluted
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
   
Amounts Due from Alumax 20,786us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLiabilitiesRecognized
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
20,786us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLiabilitiesRecognized
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
     
Alumina Supply Agreements $ 14,880us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAssetsRecognized
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
$ 14,880us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAssetsRecognized
/ us-gaap_BusinessAcquisitionAxis
= cenx_Mt.HollySmelterMember
     
[1] These amounts represents our preliminary estimates based on our current expectation of the pension, working capital, economic and other closing adjustments. These estimates are subject to review and approval by both parties. The final determination and payment of the settlement amounts is expected in the second quarter of 2015.
[2] The income attributable to the acquired Alcoa’s 50.3% stake in Mt. Holly excludes the gain on the fair value of the contingent consideration and the gain on remeasurement of the equity investment.