Debt Instrument, Convertible, Amount Exceeding Principal

No definition available.

Name:	cenx_DebtInstrumentConvertibleAmountExceedingPrincipal
Namespace Prefix:	cenx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Debt Instrument, Credit Spread Adjustment

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Periodic Payment, Percentage To Be Paid Before Termination Date

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
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Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Periodic Payment, Quarterly Installment Percent of Principal

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Redemption Premium

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Debt Instrument, Term Extension

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Variable Interest Rate

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Variable Interest Rate, Maximum Percentage

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- 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

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

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The price per share of the conversion feature embedded in the debt instrument.

+ References

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Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

+ References

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+ Details

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Period Type:	duration

- Definition

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

+ References

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+ Details

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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

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types: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
-Topic 942
-SubTopic 470
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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

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

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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

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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+ Details

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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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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1

+ Details

Name:	us-gaap_LineOfCredit
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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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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
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-Section S50
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+ Details

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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

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of loss contingency liability.

+ References

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- Definition

Amount of debt instrument classified as medium-term and current.

+ References

+ Details

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- Definition

The cash inflow from the issuance of a long-term debt instrument which can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder.

+ References

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- Definition

The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).

+ References

+ Details

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- Definition

Amount of cash outflow for short-term and long-term debt. Excludes payment of lease obligation.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition

Write-off of amounts previously capitalized as debt issuance cost in an extinguishment of debt.

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Period Type:

Debt - Narrative (Details)					1 Months Ended		3 Months Ended		9 Months Ended
Debt - Narrative (Details)	Aug. 05, 2025 USD ($)	Jul. 22, 2025	Oct. 01, 2024 USD ($)	Nov. 02, 2021 USD ($)	Jul. 31, 2025 USD ($)	Apr. 30, 2021 USD ($) $ / shares	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Dec. 09, 2022 USD ($)	Sep. 28, 2022 USD ($)	Jun. 14, 2022 USD ($)	Feb. 04, 2022 USD ($)	Nov. 30, 2013 USD ($)
Line of Credit Facility [Line Items]
Proceeds from issuance of Senior Notes due 2032									$ 400,000,000.0	$ 0
Loss on early extinguishment of debt							$ 6,200,000	$ 0	$ 6,200,000	$ 0
Senior Secured Notes, 6.875% \| Senior notes
Line of Credit Facility [Line Items]
Stated interest rate, percentage					6.875%		6.875%		6.875%
Face amount					$ 400,000,000
Proceeds from issuance of Senior Notes due 2032					$ 393,700,000
Senior Secured Notes, 6.875% \| Senior notes \| Level 2
Line of Credit Facility [Line Items]
Fair value of debt instrument							$ 415,600,000		$ 415,600,000
Senior secured notes, 7.5% \| Senior notes
Line of Credit Facility [Line Items]
Stated interest rate, percentage							7.50%		7.50%
Redemption of debt	$ 261,100,000
Redemption price, percentage	101.875%
Loss on early extinguishment of debt	$ 6,200,000
Early redemption premium	4,700,000
Write-off of deferred financing costs	$ 1,500,000
Senior convertible notes, 2.75% \| Senior notes
Line of Credit Facility [Line Items]
Stated interest rate, percentage						2.75%	2.75%		2.75%
Face amount						$ 86,300,000
Percentage of principal amount redeemed						100.00%
Payment of deferred financing fees						$ 83,700,000
Conversion ratio						0.0533547
Conversion price (in dollars per share) \| $ / shares						$ 18.74
Value exceeding principal amount									$ 48,900,000
Senior convertible notes, 2.75% \| Senior notes \| Level 2
Line of Credit Facility [Line Items]
Fair value of debt instrument							$ 140,700,000		$ 140,700,000
U.S. revolving credit facility \| U.S. revolving credit facility
Line of Credit Facility [Line Items]
Stated interest rate, percentage							7.75%		7.75%
Credit facility maximum amount													$ 250,000,000.0
Credit spread adjustment		0.10%
Outstanding borrowings							$ 0		$ 0
Outstanding letters of credit issued							49,500,000		49,500,000
Credit facility maximum amount							$ 250,000,000.0		$ 250,000,000.0
U.S. revolving credit facility \| Letter of credit
Line of Credit Facility [Line Items]
Letter of credit sub-facility amount													$ 150,000,000.0
U.S. revolving credit facility \| Foreign line of credit
Line of Credit Facility [Line Items]
Stated interest rate, percentage							7.66%		7.66%
Credit facility maximum amount							$ 100,000,000.0		$ 100,000,000.0			$ 100,000,000.0			$ 50,000,000
Outstanding borrowings							16,500,000		16,500,000
Outstanding letters of credit issued							0		0
Credit facility maximum amount														$ 80,000,000
Casthouse Facility
Line of Credit Facility [Line Items]
Credit facility maximum amount				$ 130,000,000
Debt instrument, term				8 years
Debt instrument, quarterly installment fee				1.739%
Debt instrument, remaining payment after drawdown of funds				60.00%
Medium-term notes, outstanding borrowings							$ 115,000,000		$ 115,000,000
Casthouse Facility \| Foreign line of credit
Line of Credit Facility [Line Items]
Stated interest rate, percentage							7.89%		7.89%
Vlissingen Credit Facility \| Foreign line of credit
Line of Credit Facility [Line Items]
Stated interest rate, percentage			8.75%				7.83%		7.83%
Face amount											$ 90,000,000
Credit facility maximum amount			$ 90,000,000
Term extension			2 years
Debt instrument, basis spread on variable rate			3.687%
Vlissingen Credit Facility \| Foreign line of credit \| Maximum
Line of Credit Facility [Line Items]
Variable interest rate			9.00%
Vlissingen Credit Facility \| Foreign line of credit \| Minimum
Line of Credit Facility [Line Items]
Variable interest rate			7.00%
Industrial revenue bonds, variable
Line of Credit Facility [Line Items]
Maximum variable interest rate							12.00%		12.00%
Surety Bond
Line of Credit Facility [Line Items]
Loss contingency accrual							$ 6,600,000		$ 6,600,000