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Derivatives and Financial Instruments - Additional Information (Details)
 12 Months Ended
Dec. 31, 2020
USD ($)
T
Dec. 31, 2019
USD ($)
T
Dec. 31, 2018
USD ($)
Derivative [Line Items]      
Derivative financial liabilities $ 400,000 $ 100,000  
Derivative loss deferred in equity 0 0 $ (400,000)
Derivative (loss) gain transferred to consolidated income statement $ 0 $ 100,000 $ (100,000)
Primary aluminum purchased during period, mass | T 7,000 8,000  
Long-term debt outstanding $ 53,400,000 $ 91,400,000  
Debt issuance costs 700,000 1,100,000  
LME derivative contract      
Derivative [Line Items]      
Increase In cost per $100 increase of commodity price 700,000    
Accounts and Other Receivables      
Derivative [Line Items]      
Derivative financial assets 200,000 300,000  
Bank and other loans      
Derivative [Line Items]      
Long-term debt outstanding 54,100,000 92,500,000  
Debt issuance costs 700,000 1,100,000  
Variable interest rate debt $ 4,100,000 $ 17,500,000