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

Adjustment to accretion expense impact on earnings per share basic and diluted.

No definition available.

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Namespace Prefix:	kalu_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration