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Fair Value Measurements, Schedule of Quantitative Information for Level 3 Derivative Contracts (Details) | 6 Months Ended
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Jun. 30, 2016 USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items] |
Midwest Premium Swap Liability Ending Curve Value | $ 0.073
Midwest Premium Swap Liability Beginning Curve Value | $ 0.070

X
- Definition Midwest Premium Swap Liability Beginning Curve Value + References No definition available. + Details
Name: | kalu_MidwestPremiumSwapLiabilityBeginningCurveValue
Namespace Prefix: | kalu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Midwest Premium Swap Liability Ending Curve Value + References No definition available. + Details
Name: | kalu_MidwestPremiumSwapLiabilityEndingCurveValue
Namespace Prefix: | kalu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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