Supplementary Balance Sheet Detail (Schedule Of Amounts Recognized In Balance Sheet) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Balance Sheet Related Disclosures [Abstract]
Prepaid Taxes	$ 39,837us-gaap_PrepaidTaxes	$ 25,061us-gaap_PrepaidTaxes
Accounts and notes receivable, net of allowance for doubtful accounts of $6,718 as of December 31, 2013 and $7,471 as of December 31, 2014	162,919	199,566
Raw materials and supplies	122,218	175,192
Work in process	176,141us-gaap_InventoryWorkInProcess	239,114us-gaap_InventoryWorkInProcess
Finished goods	84,544us-gaap_InventoryFinishedGoods	76,108us-gaap_InventoryFinishedGoods
Inventories	382,903us-gaap_InventoryNet	490,414us-gaap_InventoryNet
Land and improvements	36,375us-gaap_Land	37,416us-gaap_Land
Buildings	193,427us-gaap_BuildingsAndImprovementsGross	196,802us-gaap_BuildingsAndImprovementsGross
Machinery and equipment and other	1,212,120us-gaap_MachineryAndEquipmentGross	1,278,655us-gaap_MachineryAndEquipmentGross
Construction in progress	58,899us-gaap_ConstructionInProgressGross	76,007us-gaap_ConstructionInProgressGross
Property, plant and equipment	1,500,821us-gaap_PropertyPlantAndEquipmentGross	1,588,880us-gaap_PropertyPlantAndEquipmentGross
Payrolls (including incentive programs)	6,151	9,330
Customer prepayments	5,534us-gaap_CustomerAdvancesCurrent	9,599us-gaap_CustomerAdvancesCurrent
Employee compensation and benefits	8,932us-gaap_AccruedEmployeeBenefitsCurrent	10,136us-gaap_AccruedEmployeeBenefitsCurrent
Other	22,702	11,874
Accrued liabilities, net	43,319	40,939
Postretirement benefits	24,833	24,852
Pension and related benefits	65,882gti_PensionAndRelatedBenefits	54,173gti_PensionAndRelatedBenefits
Other	16,851us-gaap_OtherLongTermDebtNoncurrent	18,922us-gaap_OtherLongTermDebtNoncurrent
Other long - term obligations	107,566us-gaap_OtherLiabilitiesNoncurrent	97,947us-gaap_OtherLiabilitiesNoncurrent
Other Assets, Current	3,437us-gaap_OtherAssetsCurrent	2,117us-gaap_OtherAssetsCurrent
Other Prepaid Expense, Current	$ 9,923us-gaap_OtherPrepaidExpenseCurrent	$ 9,554us-gaap_OtherPrepaidExpenseCurrent

Pension and related benefits.

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The aggregate of amounts due from customers or clients, within one year of the balance sheet date (or one operating cycle, if longer), for goods or services that have been delivered or sold in the normal course of business and an amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date within one year of the balance sheet, reduced to their estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection and net of any write-downs taken for collection uncertainty on the part of the holder, respectively.

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Carrying value as of the balance sheet date of obligations, excluding pension and other postretirement benefits, incurred through that date and payable for perquisites provided to employees pertaining to services received from them. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities.

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Amount before accumulated depreciation of building structures held for productive use including addition, improvement, or renovation to the structure, including, but not limited to, interior masonry, interior flooring, electrical, and plumbing.

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Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

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The current portion of prepayments received from customers for goods or services to be provided in the future.

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Amount before valuation and LIFO reserves of completed merchandise or goods expected to be sold within one year or operating cycle, if longer.

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Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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Gross amount of unprocessed materials to be used in manufacturing or production process and supplies that will be consumed.

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Amount before valuation and LIFO reserves of merchandise or goods in the production process expected to be completed within one year or operating cycle, if longer.

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Amount before accumulated depletion of real estate held for productive use, excluding land held for sale.

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Amount before accumulated depreciation of tangible personal property used to produce goods and services, including, but is not limited to, tools, dies and molds, computer and office equipment.

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Carrying value as of the balance sheet date of obligations incurred through that date and payable arising from transactions not otherwise specified in the taxonomy.

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Aggregate carrying amount, as of the balance sheet date, of current assets not separately disclosed in the balance sheet. Current assets are expected to be realized or consumed within one year (or the normal operating cycle, if longer).

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Aggregate carrying amount, as of the balance sheet date, of noncurrent obligations not separately disclosed in the balance sheet. Noncurrent liabilities are expected to be paid after one year (or the normal operating cycle, if longer).

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Carrying value as of the balance sheet date of debt not otherwise defined (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

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Amount of asset related to consideration paid in advance for other costs that provide economic benefits within a future period of one year or the normal operating cycle, if longer.

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For a classified balance sheet, the carrying amount as of the balance sheet date of the portion of the obligations recognized for the various benefits provided to former or inactive employees, their beneficiaries, and covered dependents after employment but before retirement that is payable after one year (or beyond the operating cycle if longer).

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