Revenue From Contracts with Customers - Narratives (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Receivables, net of allowance for doubtful accounts	$ 183,562	$ 182,647
Accounts, Notes, Loans and Financing Receivable [Line Items]
Contract with Customer, Asset, Allowance for Credit Loss, Current		1,500
Contract with Customer, Asset, Allowance for Credit Loss, Noncurrent		1,200
Contract with Customer, Asset, before Allowance for Credit Loss	1,700	$ 2,700
Graphite Electrodes - Three-to-five-year take-or-pay contracts ("LTA")
Accounts, Notes, Loans and Financing Receivable [Line Items]
Reclassifications between long-term and current	$ (4,928)
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