XML 53 R42.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Commitments and contingencies (Details) $ in Thousands |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended | 339 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 09, 2017 USD ($) | Dec. 18, 2015 | Mar. 31, 2015 USD ($) | Apr. 30, 2013 USD ($) | Mar. 31, 2017 USD ($) MW LaborUnions | Dec. 31, 2013 USD ($) | Mar. 31, 2017 USD ($) MW LaborUnions | Dec. 31, 2016 USD ($) | Sep. 30, 2016 USD ($)
Environmental Contingencies [Abstract] |  |  |  |  |  |  |  |  |
Environmental-related accrued liabilities |  |  |  |  | $ 1,110 |  | $ 1,110 | $ 998 |
Environmental remediation expense for Hydrocarbon Recovery Plan |  |  |  |  |  |  | $ 1,085 |  |
Labor Commitments [Abstract] |  |  |  |  |  |  |  |  |
Percentage of total work force in union |  |  |  |  | 64.00% |  | 64.00% |  |
Percentage of Grundartangi work force represented by the labor unions (in hundredths) |  |  |  |  | 84.00% |  | 84.00% |  |
Number of labor unions Grundartangi subsidiary entered into a new labor agreement with | LaborUnions |  |  |  |  | 5 |  | 5 |  |
Percentage of Vlissingen work force represented by the labor union (in hundredths) |  |  |  |  | 100.00% |  | 100.00% |  |
Percentage of U.S. based work force represented by a union (in hundredths) |  |  |  |  | 54.00% |  | 54.00% |  |
PBGC Agreement [Member] |  |  |  |  |  |  |  |  |
Environmental Contingencies [Abstract] |  |  |  |  |  |  |  |  |
Required pension contributions above minimum |  |  |  | $ 17,400 |  |  |  |  |
Pension Contributions |  |  | $ 1,100 |  |  | $ 6,700 |  |  |
Pension contributions above minimum remaining |  |  |  |  | $ 9,600 |  |  |  |
Hawesville [Member] |  |  |  |  |  |  |  |  |
Legal Contingencies [Abstract] |  |  |  |  |  |  |  |  |
Power supply agreement, termination notice period |  |  |  |  | 1 year |  |  |  |
Sebree [Member] |  |  |  |  |  |  |  |  |
Legal Contingencies [Abstract] |  |  |  |  |  |  |  |  |
Power supply agreement, termination notice period |  |  |  |  | 1 year |  |  |  |
South Carolina Public Service Authority [Member] |  |  |  |  |  |  |  |  |
Legal Contingencies [Abstract] |  |  |  |  |  |  |  |  |
Power supply agreement, termination notice period |  | 60 days |  |  |  |  |  |  |
Power agreement, power supply from source one, percentage |  | 25.00% |  |  |  |  |  |  |
Power agreement, power supply from source two, percentage |  | 75.00% |  |  |  |  |  |  |
Grundartangi - HS, Landsvirkjun and OR [Member] |  |  |  |  |  |  |  |  |
OR Power Agreement [Abstract] |  |  |  |  |  |  |  |  |
Power currently available under the power purchase agreement (in megawatts) | MW |  |  |  |  | 525 |  | 525 |  |
Grundartangi - Landsvirkjun [Member] |  |  |  |  |  |  |  |  |
OR Power Agreement [Abstract] |  |  |  |  |  |  |  |  |
Power currently available under the power purchase agreement (in megawatts) | MW |  |  |  |  | 161 |  | 161 |  |
Ravenswood Retiree Medical Benefits Changes [Member] |  |  |  |  |  |  |  |  |
Environmental Contingencies [Abstract] |  |  |  |  |  |  |  |  |
Ravenswood litigation settlement amount | $ 23,000 |  |  |  |  |  |  |  |
Ravenswood litigation settlement period | 10 years |  |  |  |  |  |  |  |
Ravenswood settlement payment to be made upon final approval from court | $ 5,000 |  |  |  |  |  |  |  |
Ravenswood settlement, annual payment amount | $ 2,000 |  |  |  |  |  |  |  |
Ravenswood litigation settlement installment period | 9 years |  |  |  |  |  |  |  |
Ravenswood retiree medical benefits settlement liability |  |  |  |  |  |  |  |  | $ 23,000

X
- References No definition available. + Details
Name: | cenx_BigRiversAgreementAbstract
Namespace Prefix: | cenx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | cenx_LaborCommitmentsAbstract
Namespace Prefix: | cenx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Legal Contingencies [Abstract] + References No definition available. + Details
Name: | cenx_LegalContingenciesAbstract
Namespace Prefix: | cenx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Litigation Settlement, Annual Installment + References No definition available. + Details
Name: | cenx_LitigationSettlementAnnualInstallment
Namespace Prefix: | cenx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Litigation Settlement Installment Period + References No definition available. + Details
Name: | cenx_LitigationSettlementInstallmentPeriod
Namespace Prefix: | cenx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Litigation Settlement, Payable upon Final Approval of Settlement + References No definition available. + Details
Name: | cenx_LitigationSettlementPayableuponFinalApprovalofSettlement
Namespace Prefix: | cenx_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Litigation Settlement Period + References No definition available. + Details
Name: | cenx_LitigationSettlementPeriod
Namespace Prefix: | cenx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of labor unions representing a group of employees. + References No definition available. + Details
Name: | cenx_NumberOfLaborUnionsUnderNewLaborAgreement
Namespace Prefix: | cenx_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Pursuant to the terms of the settlement agreement with the Pension Benefit Guaranty Corporation, this amount represents the remaining additional contributions (above any minimum required contributions) to our defined benefit pension plans. + References No definition available. + Details
Name: | cenx_PensionContributionsAboveRequiredMinimumRemaining
Namespace Prefix: | cenx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Pursuant to the terms of the settlement agreement with the Pension Benefit Guaranty Corporation, we will make additional contributions (above any minimum required contributions) to our defined benefit pension plans. + References No definition available. + Details
Name: | cenx_PensionContributionsAboveRequiredMinimumTotal
Namespace Prefix: | cenx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The percentage of a Company's work force, based in the country of domicile, that are subject to collective bargaining agreements. + References No definition available. + Details
Name: | cenx_PercentageOfDomesticWorkForceInUnion
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of a Company's Icelandic work force that are subject to collective bargaining agreements. + References No definition available. + Details
Name: | cenx_PercentageOfForeignWorkForceCoveredUnderNewLaborAgreement
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of a Company's work force that are subject to collective bargaining agreements. + References No definition available. + Details
Name: | cenx_PercentageofWorkForceinUnion
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of a Company's Netherlands work force that are subject to collective bargaining agreements + References No definition available. + Details
Name: | cenx_PercentageofforeignNetherlandsworkforcerepresentedbythelaborunioninhundredths
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The power currently available under the power purchase agreement. + References No definition available. + Details
Name: | cenx_PowerAvailable
Namespace Prefix: | cenx_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Power Supply Agreement, Termination Notice Period + References No definition available. + Details
Name: | cenx_PowerSupplyAgreementTerminationNoticePeriod
Namespace Prefix: | cenx_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Short-term Power Agreement, Supply from Source One, Percentage + References No definition available. + Details
Name: | cenx_ShorttermPowerAgreementSupplyfromSourceOnePercentage
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Short-term Power Agreement, Supply from Source Two, Percentage + References No definition available. + Details
Name: | cenx_ShorttermPowerAgreementSupplyfromSourceTwoPercentage
Namespace Prefix: | cenx_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Total costs accrued as of the balance sheet date for environmental loss contingencies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346 + Details
Name: | us-gaap_AccrualForEnvironmentalLossContingencies
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13296-110859 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 + Details
Name: | us-gaap_EnvironmentalRemediationExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_EnvironmentalRemediationObligationsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Aggregate carrying amount of the estimated litigation liability for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.25) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_LitigationReserve
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of judgment or settlement awarded to (against) the entity in respect of litigation. + References No definition available. + Details
Name: | us-gaap_LitigationSettlementAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The amount of cash or cash equivalents contributed by the entity to fund its pension plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3536-108585 + Details
Name: | us-gaap_PensionContributions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_CounterpartyNameAxis=cenx_PBGCAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CounterpartyNameAxis=cenx_HawesvilleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CounterpartyNameAxis=cenx_SebreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CounterpartyNameAxis=cenx_SouthCarolinaPublicServiceAuthorityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CounterpartyNameAxis=cenx_GrundartangiHSLandsvirkjunandORMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CounterpartyNameAxis=cenx_GrundartangiLandsvirkjunMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=cenx_RavenswoodRetireeMedicalBenefitsChangesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |