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Business And Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Business And Summary Of Significant Accounting Policies [Line Items]      
Depreciation expense $ 100,400,000us-gaap_Depreciation $ 102,900,000us-gaap_Depreciation $ 59,600,000us-gaap_Depreciation
Capitalized bank fees 9,700,000gti_CapitalizedBankFeesUponIncurrenceOfDebt 9,800,000gti_CapitalizedBankFeesUponIncurrenceOfDebt  
Amortization of capitalized bank fees 3,339,000us-gaap_AmortizationOfFinancingCosts 2,504,000us-gaap_AmortizationOfFinancingCosts 1,712,000us-gaap_AmortizationOfFinancingCosts
Environmental remediation, compliance and management expenses 17,000,000us-gaap_EnvironmentalRemediationExpense 14,600,000us-gaap_EnvironmentalRemediationExpense 15,800,000us-gaap_EnvironmentalRemediationExpense
Accrued liability relating to environmental remediation 6,900,000us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses 7,000,000us-gaap_AccrualForEnvironmentalLossContingenciesProvisionForNewLosses  
Total costs capitalized 15,600,000us-gaap_CapitalizedSoftwareDevelopmentCostsForSoftwareSoldToCustomers 17,800,000us-gaap_CapitalizedSoftwareDevelopmentCostsForSoftwareSoldToCustomers  
Amortization expense 500,000us-gaap_CapitalizedComputerSoftwareAmortization 1,000,000us-gaap_CapitalizedComputerSoftwareAmortization 1,400,000us-gaap_CapitalizedComputerSoftwareAmortization
Deferred costs 13,300,000us-gaap_OtherDeferredCostsGross 7,500,000us-gaap_OtherDeferredCostsGross  
Amortized costs 6,600,000us-gaap_AccumulatedAmortizationOfOtherDeferredCosts 7,800,000us-gaap_AccumulatedAmortizationOfOtherDeferredCosts  
Quantifying Misstatement in Current Year Financial Statements, Amount 2,700,000us-gaap_QuantifyingMisstatementInCurrentYearFinancialStatementsAmount    
Quantifying Misstatement of Current Year Financial Statements, Amount Net of Tax 1,800,000gti_QuantifyingMisstatementOfCurrentYearFinancialStatementsAmountNetOfTax    
Capitalized Bank Fees [Member]      
Business And Summary Of Significant Accounting Policies [Line Items]      
Amortization of capitalized bank fees $ 3,300,000us-gaap_AmortizationOfFinancingCosts
/ us-gaap_IncomeStatementLocationAxis
= gti_CapitalizedBankFeesMember		 $ 2,500,000us-gaap_AmortizationOfFinancingCosts
/ us-gaap_IncomeStatementLocationAxis
= gti_CapitalizedBankFeesMember		 $ 1,700,000us-gaap_AmortizationOfFinancingCosts
/ us-gaap_IncomeStatementLocationAxis
= gti_CapitalizedBankFeesMember