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Curtailment of Operations - Hawesville (Details) - Curtailment Of Operations - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2024 | Mar. 31, 2023
Restructuring Cost and Reserve [Line Items] |  |
Severance costs | $ 0.6 | $ 7.0
Gain (loss) on material sales | $ 0.5 | 0.7
Temporary Facility Closing, Excess Capacity |  |
Restructuring Cost and Reserve [Line Items] |  |
Excess capacity charges |  | $ 5.4

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