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Supplementary Balance Sheet Details (Details) - USD ($) $ in Millions | Mar. 31, 2023 | Dec. 31, 2022
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Payables and Accruals [Abstract] |  |
Supplier Finance Program Obligation Current | $ 7.0 | $ 0.0

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- Definition Supplier Finance Program Obligation Current + References No definition available. + Details
Name: | gti_SupplierFinanceProgramObligationCurrent
Namespace Prefix: | gti_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_PayablesAndAccrualsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration