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Supplemental Guarantor Information Balance Sheet (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
ASSETS          
Cash and cash equivalents $ 17,550us-gaap_CashAndCashEquivalentsAtCarryingValue $ 11,888us-gaap_CashAndCashEquivalentsAtCarryingValue $ 17,317us-gaap_CashAndCashEquivalentsAtCarryingValue $ 12,429us-gaap_CashAndCashEquivalentsAtCarryingValue $ 12,429us-gaap_CashAndCashEquivalentsAtCarryingValue
Accounts receivable - affiliates 0us-gaap_AccountsReceivableRelatedPartiesCurrent 0us-gaap_AccountsReceivableRelatedPartiesCurrent      
Accounts receivable - trade 162,919us-gaap_AccountsReceivableNetCurrent 199,566us-gaap_AccountsReceivableNetCurrent      
Inventories 382,903us-gaap_InventoryNet 490,414us-gaap_InventoryNet      
Prepaid expenses and other current assets 81,623us-gaap_PrepaidExpenseCurrent 73,790us-gaap_PrepaidExpenseCurrent      
Total current assets 644,995us-gaap_AssetsCurrent 775,658us-gaap_AssetsCurrent      
Investment in affiliates 0us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue 0us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue      
Net property, plant and equipment 654,040us-gaap_PropertyPlantAndEquipmentNet [1] 820,985us-gaap_PropertyPlantAndEquipmentNet [1]      
Deferred income taxes 16,819us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent 10,334us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent      
Goodwill 420,129us-gaap_Goodwill 496,810us-gaap_Goodwill 498,261us-gaap_Goodwill    
Notes receivable - affiliate 0us-gaap_NotesReceivableRelatedPartiesNoncurrent 0us-gaap_NotesReceivableRelatedPartiesNoncurrent      
Other assets 97,822us-gaap_OtherAssetsNoncurrent 114,061us-gaap_OtherAssetsNoncurrent      
Total assets 1,833,805us-gaap_Assets 2,217,848us-gaap_Assets      
LIABILITIES AND STOCKHOLDERS’ EQUITY          
Accounts payable - affiliate 0us-gaap_AccountsPayableRelatedPartiesCurrent 0us-gaap_AccountsPayableRelatedPartiesCurrent      
Accounts payable - trade 86,409us-gaap_AccountsPayableCurrent 115,212us-gaap_AccountsPayableCurrent      
Short-term debt 188,104us-gaap_ShortTermBorrowings 1,161us-gaap_ShortTermBorrowings      
Accrued income and other taxes 24,506us-gaap_TaxesPayableCurrent 30,687us-gaap_TaxesPayableCurrent      
Rationalizations 9,563gti_RestructuringandRelatedLiability 18,421gti_RestructuringandRelatedLiability      
Supply chain financing liability 0us-gaap_OtherShortTermBorrowings 9,455us-gaap_OtherShortTermBorrowings      
Other accrued liabilities 43,319us-gaap_OtherAccruedLiabilitiesCurrent 40,939us-gaap_OtherAccruedLiabilitiesCurrent      
Total current liabilities 351,901us-gaap_LiabilitiesCurrent 215,875us-gaap_LiabilitiesCurrent      
Long-term debt - affiliate 0us-gaap_DueToRelatedPartiesNoncurrent 0us-gaap_DueToRelatedPartiesNoncurrent      
Long-term debt - third party 341,615us-gaap_LongTermDebtNoncurrent 541,593us-gaap_LongTermDebtNoncurrent      
Other long-term obligations 107,566us-gaap_OtherLiabilitiesNoncurrent 97,947us-gaap_OtherLiabilitiesNoncurrent      
Deferred income taxes 28,197us-gaap_DeferredTaxLiabilitiesNoncurrent 41,684us-gaap_DeferredTaxLiabilitiesNoncurrent      
Total stockholders’ equity 1,004,526us-gaap_StockholdersEquity 1,320,749us-gaap_StockholdersEquity 1,349,851us-gaap_StockholdersEquity 1,339,944us-gaap_StockholdersEquity  
Total liabilities and stockholders’ equity 1,833,805us-gaap_LiabilitiesAndStockholdersEquity 2,217,848us-gaap_LiabilitiesAndStockholdersEquity      
Parent Company [Member]          
ASSETS          
Cash and cash equivalents 0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
366us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
 
Accounts receivable - affiliates 40,474us-gaap_AccountsReceivableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
42,410us-gaap_AccountsReceivableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Accounts receivable - trade 0us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Inventories 0us-gaap_InventoryNet
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_InventoryNet
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Prepaid expenses and other current assets 0us-gaap_PrepaidExpenseCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_PrepaidExpenseCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Total current assets 40,474us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
42,410us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Investment in affiliates 1,414,278us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
1,709,914us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Net property, plant and equipment 0us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Deferred income taxes 0us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Goodwill 0us-gaap_Goodwill
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_Goodwill
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Notes receivable - affiliate 35,722us-gaap_NotesReceivableRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
51,090us-gaap_NotesReceivableRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Other assets 4,110us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
4,752us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Total assets 1,494,584us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
1,808,166us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
LIABILITIES AND STOCKHOLDERS’ EQUITY          
Accounts payable - affiliate 0us-gaap_AccountsPayableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_AccountsPayableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Accounts payable - trade 47us-gaap_AccountsPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_AccountsPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Short-term debt 187,973us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Accrued income and other taxes 344us-gaap_TaxesPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
2,678us-gaap_TaxesPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Rationalizations 0gti_RestructuringandRelatedLiability
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0gti_RestructuringandRelatedLiability
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Supply chain financing liability 0us-gaap_OtherShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_OtherShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Other accrued liabilities 2,444us-gaap_OtherAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
2,444us-gaap_OtherAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Total current liabilities 190,808us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
5,122us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Long-term debt - affiliate 0us-gaap_DueToRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_DueToRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Long-term debt - third party 300,000us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
475,675us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Other long-term obligations 0us-gaap_OtherLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
0us-gaap_OtherLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Deferred income taxes 0us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
6,620us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Total stockholders’ equity 1,003,776us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
1,320,749us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Total liabilities and stockholders’ equity 1,494,584us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
1,808,166us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
     
Guarantor Subsidiaries [Member]          
ASSETS          
Cash and cash equivalents 5,503us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
4,752us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
4,425us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
3,503us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
 
Accounts receivable - affiliates 35,618us-gaap_AccountsReceivableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
28,551us-gaap_AccountsReceivableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Accounts receivable - trade 45,861us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
48,998us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Inventories 148,080us-gaap_InventoryNet
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
174,935us-gaap_InventoryNet
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Prepaid expenses and other current assets 17,336us-gaap_PrepaidExpenseCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
22,555us-gaap_PrepaidExpenseCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Total current assets 252,398us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
279,791us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Investment in affiliates 762,251us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
828,012us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Net property, plant and equipment 431,602us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
540,273us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Deferred income taxes 0us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
0us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Goodwill 217,099us-gaap_Goodwill
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
293,162us-gaap_Goodwill
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Notes receivable - affiliate 7,413us-gaap_NotesReceivableRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
7,413us-gaap_NotesReceivableRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Other assets 45,617us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
53,447us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Total assets 1,716,380us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
2,002,098us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
LIABILITIES AND STOCKHOLDERS’ EQUITY          
Accounts payable - affiliate 80,659us-gaap_AccountsPayableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
58,206us-gaap_AccountsPayableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Accounts payable - trade 35,435us-gaap_AccountsPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
41,971us-gaap_AccountsPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Short-term debt 131us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
165us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Accrued income and other taxes 3,380us-gaap_TaxesPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
4,736us-gaap_TaxesPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Rationalizations 7,538gti_RestructuringandRelatedLiability
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
1,890gti_RestructuringandRelatedLiability
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Supply chain financing liability 0us-gaap_OtherShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
0us-gaap_OtherShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Other accrued liabilities 15,252us-gaap_OtherAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
12,404us-gaap_OtherAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Total current liabilities 142,395us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
119,372us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Long-term debt - affiliate 35,722us-gaap_DueToRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
51,090us-gaap_DueToRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Long-term debt - third party 40,393us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
50,525us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Other long-term obligations 77,724us-gaap_OtherLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
66,590us-gaap_OtherLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Deferred income taxes 5,118us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
4,607us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Total stockholders’ equity 1,415,028us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
1,709,914us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Total liabilities and stockholders’ equity 1,716,380us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
2,002,098us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
     
Non-Guarantor Subsidiaries [Member]          
ASSETS          
Cash and cash equivalents 12,047us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
7,136us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
12,892us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
8,560us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
 
Accounts receivable - affiliates 40,185us-gaap_AccountsReceivableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
15,824us-gaap_AccountsReceivableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Accounts receivable - trade 117,058us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
150,568us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Inventories 234,823us-gaap_InventoryNet
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
315,479us-gaap_InventoryNet
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Prepaid expenses and other current assets 64,287us-gaap_PrepaidExpenseCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
51,235us-gaap_PrepaidExpenseCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Total current assets 468,400us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
540,242us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Investment in affiliates 0us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Net property, plant and equipment 222,438us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
280,712us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Deferred income taxes 16,819us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
10,334us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Goodwill 203,030us-gaap_Goodwill
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
203,648us-gaap_Goodwill
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Notes receivable - affiliate 0us-gaap_NotesReceivableRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
0us-gaap_NotesReceivableRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Other assets 48,095us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
55,862us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Total assets 958,782us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
1,090,798us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
LIABILITIES AND STOCKHOLDERS’ EQUITY          
Accounts payable - affiliate 35,618us-gaap_AccountsPayableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
28,579us-gaap_AccountsPayableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Accounts payable - trade 50,927us-gaap_AccountsPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
73,241us-gaap_AccountsPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Short-term debt 0us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
996us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Accrued income and other taxes 20,782us-gaap_TaxesPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
23,273us-gaap_TaxesPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Rationalizations 2,025gti_RestructuringandRelatedLiability
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
16,531gti_RestructuringandRelatedLiability
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Supply chain financing liability 0us-gaap_OtherShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
9,455us-gaap_OtherShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Other accrued liabilities 25,623us-gaap_OtherAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
26,091us-gaap_OtherAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Total current liabilities 134,975us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
178,166us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Long-term debt - affiliate 7,413us-gaap_DueToRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
7,413us-gaap_DueToRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Long-term debt - third party 1,222us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
15,393us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Other long-term obligations 29,842us-gaap_OtherLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
31,357us-gaap_OtherLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Deferred income taxes 23,079us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
30,457us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Total stockholders’ equity 762,251us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
828,012us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Total liabilities and stockholders’ equity 958,782us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
1,090,798us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember
     
Consolidating Entries and Eliminations [Member]          
ASSETS          
Cash and cash equivalents 0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
 
Accounts receivable - affiliates (116,277)us-gaap_AccountsReceivableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(86,785)us-gaap_AccountsReceivableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Accounts receivable - trade 0us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_AccountsReceivableNetCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Inventories 0us-gaap_InventoryNet
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_InventoryNet
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Prepaid expenses and other current assets 0us-gaap_PrepaidExpenseCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_PrepaidExpenseCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Total current assets (116,277)us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(86,785)us-gaap_AssetsCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Investment in affiliates (2,176,529)us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(2,537,926)us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValue
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Net property, plant and equipment 0us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_PropertyPlantAndEquipmentNet
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Deferred income taxes 0us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_DeferredTaxAssetsLiabilitiesNetNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Goodwill 0us-gaap_Goodwill
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_Goodwill
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Notes receivable - affiliate (43,135)us-gaap_NotesReceivableRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(58,503)us-gaap_NotesReceivableRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Other assets 0us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_OtherAssetsNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Total assets (2,335,941)us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(2,683,214)us-gaap_Assets
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
LIABILITIES AND STOCKHOLDERS’ EQUITY          
Accounts payable - affiliate (116,277)us-gaap_AccountsPayableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(86,785)us-gaap_AccountsPayableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Accounts payable - trade 0us-gaap_AccountsPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_AccountsPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Short-term debt 0us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Accrued income and other taxes 0us-gaap_TaxesPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_TaxesPayableCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Rationalizations 0gti_RestructuringandRelatedLiability
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0gti_RestructuringandRelatedLiability
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Supply chain financing liability 0us-gaap_OtherShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_OtherShortTermBorrowings
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Other accrued liabilities 0us-gaap_OtherAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_OtherAccruedLiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Total current liabilities (116,277)us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(86,785)us-gaap_LiabilitiesCurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Long-term debt - affiliate (43,135)us-gaap_DueToRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(58,503)us-gaap_DueToRelatedPartiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Long-term debt - third party 0us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_LongTermDebtNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Other long-term obligations 0us-gaap_OtherLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_OtherLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Deferred income taxes 0us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
0us-gaap_DeferredTaxLiabilitiesNoncurrent
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Total stockholders’ equity (2,176,529)us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
(2,537,926)us-gaap_StockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
Total liabilities and stockholders’ equity $ (2,335,941)us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
$ (2,683,214)us-gaap_LiabilitiesAndStockholdersEquity
/ dei_LegalEntityAxis
= us-gaap_ConsolidationEliminationsMember
     
[1] Long-lived assets represent fixed assets, net of accumulated depreciation.