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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 |  | $ 1,042 us-gaap_PaymentsToAcquireBusinessesGross |  | $ 48,058 us-gaap_PaymentsToAcquireBusinessesGross | $ 0 us-gaap_PaymentsToAcquireBusinessesGross |  |
Gain on fair value of contingent consideration | 7,943 us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsRevenuesAndGainsRecognized | 7,943 us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsRevenuesAndGainsRecognized |  | 0 us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsRevenuesAndGainsRecognized | 0 us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsRevenuesAndGainsRecognized |  |
Gain on remeasurement of equity investment | 1,318 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain | 1,318 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain |  | 0 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain | 0 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain |  |
Contingent consideration | 5,837 us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent | 5,837 us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent |  | 0 us-gaap_BusinessCombinationContingentConsiderationLiabilityNoncurrent |  |  |
Pension asset (1) | 30,842 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets | 30,842 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets |  | 0 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets |  |  |
Mt. Holly Smelter [Member] |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |
Purchase price cash paid |  | 53,831 us-gaap_PaymentsToAcquireBusinessesGross / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |  |  |  |  |
Acquisition-related costs | 1,087 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember | 1,087 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |  |  |  |  |
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High |  |  |  |  |  | 22,500 us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low |  |  |  |  |  | 12,500 us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Gain on fair value of contingent consideration |  | 7,943 us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsRevenuesAndGainsRecognized / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |  |  |  |  |
Gain on remeasurement of equity investment |  | 1,318 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |  |  |  |  |
Purchase price |  |  |  |  |  | 67,500 cenx_BusinessAcquisitionPurchasePrice / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Pension funding (1) |  |  |  |  |  | 46,546 us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember | [1]
Contingent consideration |  |  |  |  |  | 13,780 us-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 |  |  |  |  |  | 56,723 us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1 / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Total consideration |  |  |  |  |  | 149,053 us-gaap_BusinessCombinationConsiderationTransferred1 / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Inventories |  |  |  |  |  | 26,105 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Due from Alumax |  |  |  |  |  | 20,786 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Prepaid and other current assets |  |  |  |  |  | 2,527 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Intangible asset |  |  |  |  |  | 2,580 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Pension asset (1) |  |  |  |  |  | 30,842 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember | [1]
Property, plant and equipment – net |  |  |  |  |  | 127,089 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Total assets acquired |  |  |  |  |  | 209,929 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Accounts payable, trade |  |  |  |  |  | 41,471 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Accrued and other current liabilities |  |  |  |  |  | 8,335 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Accrued postretirement benefit costs |  |  |  |  |  | 2,857 cenx_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedPostRetirementBenefits / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember | [1]
Other liabilities |  |  |  |  |  | 8,213 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Deferred taxes |  |  |  |  |  | 4,804 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilitiesNoncurrent / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Total liabilities assumed |  |  |  |  |  | 65,680 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Goodwill |  |  |  |  |  | 4,804 us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |
Mt. Holly revenue |  | 25,911 us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |  |  |  |  |
Mt. Holly income from continuing operations (1) |  | 3,024 us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember | [2] |  |  |  |
Pro forma revenues |  | 2,176,552 us-gaap_BusinessAcquisitionsProFormaRevenue / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |  | 1,707,838 us-gaap_BusinessAcquisitionsProFormaRevenue / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |  |  |
Pro forma earnings (loss) from continuing operations |  | 125,847 us-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 |  | $ 1.30 us-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 |  | $ 1.29 us-gaap_BusinessAcquisitionProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTaxPerShareDiluted / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |  | $ (0.44)us-gaap_BusinessAcquisitionProFormaIncomeLossFromContinuingOperationsBeforeChangesInAccountingAndExtraordinaryItemsNetOfTaxPerShareDiluted / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |  |  |
Amounts Due from Alumax | 20,786 us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLiabilitiesRecognized / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember | 20,786 us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsLiabilitiesRecognized / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember |  |  |  |  |
Alumina Supply Agreements | $ 14,880 us-gaap_BusinessCombinationSeparatelyRecognizedTransactionsAssetsRecognized / us-gaap_BusinessAcquisitionAxis = cenx_Mt.HollySmelterMember | $ 14,880 us-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.

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- Definition Amount of intangible assets, excluding goodwill, acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 + Details
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- Definition The amount of inventory recognized as of the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=35744172&loc=d3e2207-128464 + Details
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- Definition Amount of liabilities assumed at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 + Details
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- Definition Amount of other liabilities due after one year or the normal operating cycle, if longer, assumed at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 + Details
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- Definition Amount of other assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 + Details
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- Definition The amount of property, plant, and equipment recognized as of the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=35744172&loc=d3e2207-128464 + Details
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- Definition The assets recognized for each amount of assets recorded in a transaction with the acquiree that is recognized separately from the acquisition of assets and assumptions of liabilities in the business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(3) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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- Definition The amount of liabilities recognized recorded in a transaction with the acquiree for each transaction that is recognized separately from the acquisition of assets and assumptions of liabilities in the business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(3) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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- Definition The revenues and gains recognized recorded for each transaction with the acquiree that is recognized separately from the acquisition of assets and assumptions of liabilities in the business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(3) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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- Definition Fair value at acquisition-date of the equity interest in the acquiree held by the acquirer, immediately before the acquisition date for businesses combined in stages. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g)(1) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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- Definition In a business combination achieved in stages, this element represents the amount of gain recognized by the entity as a result of remeasuring to fair value the equity interest in the acquiree it held before the business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g)(2) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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- Definition The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3213-108585 + Details
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