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Long-Term Debt And Liquidity Long-Term Debt And Liquidity (Senior Notes) (Details) (Senior Notes [Member], USD $)
In Millions, unless otherwise specified
Nov. 20, 2012
Dec. 31, 2014
Debt Instrument [Line Items]    
Principal amount issued $ 300us-gaap_DebtInstrumentFaceAmount  
Stated interest rate 6.375%us-gaap_DebtInstrumentInterestRateStatedPercentage  
Redemption price percentage of principal prior to November 15, 2016 100.00%gti_RedemptionPricePercentageOfPrincipalPriorToNovember152016  
Redemption price percentage of principal prior to November 15, 2015 106.375%gti_RedemptionPricePercentageOfPrincipalPriorToNovember152015  
Repurchase percentage price of aggregate principal due to change in control 101.00%gti_RepurchasePercentagePriceOfAggregatePrincipalDueToChangeInControl  
Maximum [Member]    
Debt Instrument [Line Items]    
Redemption percentage price of aggregate principal prior to November 15, 2015 35.00%gti_AggregatePrincipalRedemptionPercentagePricePriorToNovember152015
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Minimum [Member]    
Debt Instrument [Line Items]    
Unpaid indebtness after maturity or acceleration   50.0gti_UnpaidIndebtnessAfterMaturityOrAcceleration
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Unpaid judgment or decree   $ 50.0gti_UnpaidJudgmentOrDecree
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember