Organization And Summary Of Significant Accounting Policies (Details) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($) major_product_categories	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]		us-gaap:AccountingStandardsUpdate201613Member
Total stockholders' equity	$ 233,841	$ 691,073	$ 329,385	$ 680,379
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	36.60%
Retained Earnings (Accumulated Deficit)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total stockholders' equity	$ 974,852	$ 1,451,836	$ 1,070,770	$ 1,374,844