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v3.19.3.a.u2

Quarterly Information (Unaudited) - Financial Results Overview (Details) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2018 USD ($) | Jun. 30, 2018 pot_line | Dec. 31, 2019 USD ($)
Effect of Fourth Quarter Events [Line Items] |  |  |
Inventory adjustments |  |  | $ (30.6)
Number of potlines, temporary curtailment | pot_line |  | 1 |
BHH [Member] |  |  |
Effect of Fourth Quarter Events [Line Items] |  |  |
Loss on sale of equity investments |  |  | $ 4.3
Helguvik [Member] |  |  |
Effect of Fourth Quarter Events [Line Items] |  |  |
Gain on extinguishment of liability | $ 4.5 |  |

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