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Fair Value Measurements Fair Value Measurements, Schedule of Quantitative Information for Level 3 Derivative Contracts (Details) | 6 Months Ended
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Jun. 30, 2015 USD ($)
Fair Value Inputs, Assets, Quantitative Information [Line Items] |
Midwest Premium Swap Beginning Curve Value | $ 0.082
Midwest Premium Swap Contracts Ending Curve Value | $ 0.070

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

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

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- 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