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Derivative instruments (Details)	Sep. 30, 2016 t
LME Swap [Member]
Derivative [Line Items]
Primary aluminum capacity	45,000
Price Swap [Member]
Derivative [Line Items]
Primary aluminum capacity	8,200

X

- Definition

Annual production capacity of primary aluminum (in tonnes).

+ References

No definition available.

+ Details

Name:	cenx_Primaryaluminumcapacity
Namespace Prefix:	cenx_
Data Type:	num:massItemType
Balance Type:	na
Period Type:	instant

X

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

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cenx_FixedtoVariableLondonMetalsExchangeSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cenx_FixedtoFloatingSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: