Debt Instrument Interest Rate Stated Percentage Additional Notes Or Cash

No definition available.

Name:	cenx_DebtInstrumentInterestRateStatedPercentageAdditionalNotesOrCash
Namespace Prefix:	cenx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

DebtInstrumentInterestRateStatedPercentageCash

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Payment Terms, Number of Monthly Payments

+ References

No definition available.

+ Details

Name:	cenx_DebtInstrumentPaymentTermsNumberofMonthlyPayments
Namespace Prefix:	cenx_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of additional borrowings provided in credit facility under a letter of credit sub-facility.

+ References

No definition available.

+ Details

Name:	cenx_LineOfCreditFacilityAdditionalBorrowingsUnderLetterOfCreditSubFacility
Namespace Prefix:	cenx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line of Credit Facility, Remaining Borrowing Capacity, Net of Letters of Credit

+ References

No definition available.

+ Details

Name:	cenx_LineofCreditFacilityRemainingBorrowingCapacityNetofLettersofCredit
Namespace Prefix:	cenx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

+ Details

Name:	us-gaap_DebtInstrumentFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentRedemptionPricePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of obligations due all related parties.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k)(1))
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 4
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
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Balance Type:
Period Type:

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=us-gaap_ShortTermDebtMember
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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_ForeignLineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=cenx_HawesvilleMember
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Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cenx_SeniorSecuredNotesDueJune012025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LongTermDebtMember
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Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=cenx_U.SRevolvingCreditFacilityAccordionMember
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Balance Type:
Period Type:

- Details

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Period Type:

Debt - Credit Facility (Details)			3 Months Ended	12 Months Ended
Debt - Credit Facility (Details)	Jul. 01, 2020 USD ($)	Apr. 29, 2019 USD ($) installment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2020 USD ($)
Line of Credit Facility [Line Items]
Proceeds from issuance of debt				$ 243,800,000	$ 0	$ 0
Loss on early extinguishment of debt				(1,200,000)	$ 0	$ 0
U.S revolving credit facility [Member]
Line of Credit Facility [Line Items]
Credit facility maximum amount				175,000,000.0
Borrowing availability				129,900,000
Outstanding letters of credit issued				34,300,000
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letter of credit sub-facility amount				95,600,000
Short-term Debt [Member] \| Letter of Credit [Member]
Line of Credit Facility [Line Items]
Outstanding borrowings				0
Short-term Debt [Member] \| Iceland revolving credit facility [Member]
Line of Credit Facility [Line Items]
Outstanding borrowings				45,000,000.0
Hawesville [Member]
Line of Credit Facility [Line Items]
Due to related parties		$ 40,000,000.0
Number of monthly payments \| installment		24
Hawesville [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate		5.375%
Senior secured notes due June 01, 2025 [Member]
Line of Credit Facility [Line Items]
Proceeds from issuance of debt	$ 243,800,000
Senior secured notes due June 01, 2025 [Member] \| Level 2
Line of Credit Facility [Line Items]
Fair value of debt instrument				265,000,000.0
Long-term Debt [Member] \| U.S revolving credit facility [Member]
Line of Credit Facility [Line Items]
Credit facility face amount				175,000,000.0
Long-term Debt [Member] \| Letter of Credit [Member]
Line of Credit Facility [Line Items]
Letter of credit sub-facility amount				110,000,000.0
Long-term Debt [Member] \| U.S revolving credit facility, accordion [Member]
Line of Credit Facility [Line Items]
Credit facility face amount				50,000,000.0
Long-term Debt [Member] \| Iceland revolving credit facility [Member]
Line of Credit Facility [Line Items]
Credit facility maximum amount				50,000,000.0
Borrowing availability				5,000,000.0
Outstanding letters of credit issued				0
Borrowing availability, net of outstanding letters of credit and borrowings				$ 5,000,000.0
Long-term Debt [Member] \| Senior secured notes due June 01, 2025 [Member]
Line of Credit Facility [Line Items]
Stated interest rate				12.00%
Face amount	$ 250,000,000.0
Interest rate, cash percentage	10.00%
Interest rate, additional notes or cash percentage	2.00%
Redemption price, percentage				100.00%
Long-term Debt [Member] \| Senior secured notes due June 01, 2021 [Member]
Line of Credit Facility [Line Items]
Stated interest rate				7.50%			7.50%
Face amount							$ 243,700,000
Redemption price, percentage				100.00%
Loss on early extinguishment of debt			$ 1,200,000	$ 1,200,000