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v3.21.1

Business, Product and Geographical Area Information - Additional Information (Details) | 3 Months Ended
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Mar. 31, 2021 Productionfacility
Domestic |
Segment Reporting Information [Line Items] |
Number of production facilities | 13
Canada |
Segment Reporting Information [Line Items] |
Number of production facilities | 1

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- Definition Number of Production Facilities. + References No definition available. + Details
Name: | kalu_NumberOfProductionFacilities
Namespace Prefix: | kalu_
Data Type: | xbrli:integerItemType
Balance Type: | na
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_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_StatementGeographicalAxis=country_US
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=country_CA
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |