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Retirement Plans And Postretirement Benefits (Assumptions Used To Determine Net Pension Costs And Projected Benefit Obligations) (Details) (Pension Benefit Obligations [Member])
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Weighted average assumptions to determine net cost:    
Discount rate 4.20%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate 3.58%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
Expected return on plan assets 4.77%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets 4.29%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets
Rate of compensation increase 2.42%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease 2.44%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostRateOfCompensationIncrease
Retirement Plans [Member]    
Weighted average assumptions to determine benefit obligations:    
Discount rate 3.33%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= gti_PensionBenefitObligationsMember
4.20%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= gti_PensionBenefitObligationsMember
Rate of compensation increase 2.08%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= gti_PensionBenefitObligationsMember
2.42%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_PensionPlansDefinedBenefitMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= gti_PensionBenefitObligationsMember