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Commitments and Contingencies - Summary of Activities Relating to Company's CARO Liabilities (Parenthetical) (Details) - $ / shares | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Commitments And Contingencies Disclosure [Abstract] |  |
Adjustment to accretion expense, impact on basic and diluted net income per share | $ 0.01 | $ 0.01

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- Definition Adjustment to accretion expense impact on earnings per share basic and diluted. + References No definition available. + Details
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Namespace Prefix: | kalu_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
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