Organization And Summary Of Significant Accounting Policies (Details) $ / shares in Units, $ in Thousands	1 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	May 26, 2021	Jun. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) major_product_categories	Dec. 31, 2020 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Apr. 26, 2018 $ / shares shares
Accounting Policies [Abstract]
Shares, Issued | shares										38,097,525
Sale of Stock, Price Per Share | $ / shares										$ 15.00
Number of major product categories | major_product_categories			2
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]		Accounting Standards Update 2016-13 [Member]
Total stockholders' equity		$ 574,714	$ 110,701	$ 329,385	$ 176,560	$ 233,841	$ 472,107	$ 680,379	$ 691,073
GrafTech International Ltd | Brookfield
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions	24.00%		24.20%	55.30%
Retained Earnings (Accumulated Deficit)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total stockholders' equity		$ 1,284,756	$ 869,311	$ 1,070,770	$ 952,400	$ 974,852	$ 1,193,194	$ 1,374,844	$ 1,451,836