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Revenue From Contracts with Customers - Narratives (Details) - USD ($)
$ in Thousands
 6 Months Ended
Jun. 30, 2021
Dec. 31, 2020
Revenue from Contract with Customer [Abstract]    
Receivables, net of allowance for doubtful accounts $ 173,409 $ 182,647
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Contract with Customer, Asset, Allowance for Credit Loss, Current 1,800 1,500
Contract with Customer, Asset, Allowance for Credit Loss, Noncurrent 300 1,200
Contract with Customer, Asset, before Allowance for Credit Loss 2,100 $ 2,700
Graphite Electrodes - Three-to-five-year take-or-pay contracts    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Reclassifications between long-term and current $ (4,404)  
Minimum    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Accounts receivable payment terms 30 days  
Maximum    
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Accounts receivable payment terms 120 days