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Contingencies (Details) - USD ($) $ in Thousands	1 Months Ended		9 Months Ended	12 Months Ended
Contingencies (Details) - USD ($) $ in Thousands	Jun. 30, 2021	May 26, 2021	Sep. 30, 2021	Dec. 31, 2020
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease)
Balance as of December 31, 2020			$ 1,997
Product warranty accruals and adjustments			1,112
Settlements			(1,818)
Balance as of September 30, 2021			$ 1,291	$ 1,997
Loss Contingencies
Related party tax agreement percent of savings			85.00%
Due to Related Parties			$ 19,100	40,900
due to related party			3,922	21,752
Long-term debt - affiliate			$ 15,176	$ 19,098
Outstanding Voting Power Percentage Scenario 1			30.00%
Long-term Incentive Plan
Loss Contingencies
Loss Contingency Accrual, Payments			$ 66,700
Fixed Price LTAs
Loss Contingencies
Relief/reimbursement sought	$ 61,000
GrafTech International Ltd \| Brookfield
Loss Contingencies
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions		24.00%	24.20%	55.30%
Cost of sales \| Long-term Incentive Plan
Loss Contingencies
Loss Contingency, Loss in Period			$ 30,700
Selling, General and Administrative Expenses \| Long-term Incentive Plan
Loss Contingencies
Loss Contingency, Loss in Period			$ 42,700
LIBO
Loss Contingencies
Due to Related Party, Basis Spread on Variable Rate			0.0100
Minimum \| Long-term Incentive Plan
Loss Contingencies
Loss Contingency, Loss in Period			$ 73,400
Profit Units [Member] \| Long-term Incentive Plan
Loss Contingencies
Number of shares authorized			30,000
Award vesting period			5 years
Outstanding Voting Power Percentage Minimum			0.30