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Summary of Significant Accounting Policies (Schedule of Reclassifications Out of AOCI) (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Cost of goods sold | $ (778,113)us-gaap_CostOfGoodsSold |  | $ (784,675)us-gaap_CostOfGoodsSold |  | $ (712,660)us-gaap_CostOfGoodsSold |
Income taxes | 9,387 us-gaap_IncomeTaxExpenseBenefit | [1] | 16,995 us-gaap_IncomeTaxExpenseBenefit | [1] | 18,319 us-gaap_IncomeTaxExpenseBenefit | [1]
Gain (loss) on derivative financial instruments | Reclassification out of Accumulated Other Comprehensive Income |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Total, before taxes | 647 us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  | (583)us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  |  |
Income taxes | 244 us-gaap_IncomeTaxExpenseBenefit / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  | (221)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  |  |
Total, net of tax | 403 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  | (362)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  |  |
Pension and other post-retirement benefit adjustments | Reclassification out of Accumulated Other Comprehensive Income |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Actuarial gain (loss) and prior service costs, before taxes | (10,579)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | [2] | (14,818)us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossBeforeTax / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | [2] |  |
Income taxes | (3,582)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |  | (5,398)us-gaap_IncomeTaxExpenseBenefit / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |  |  |
Total, net of tax | (6,997)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |  | (9,420)us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |  |  |
Aluminum Futures Contracts | Gain (loss) on derivative financial instruments | Reclassification out of Accumulated Other Comprehensive Income |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Cost of goods sold | 631 us-gaap_CostOfGoodsSold / us-gaap_DerivativeInstrumentRiskAxis = tg_AluminumFuturesContractsMember / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  | (583)us-gaap_CostOfGoodsSold / us-gaap_DerivativeInstrumentRiskAxis = tg_AluminumFuturesContractsMember / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  |  |
Foreign Currency Forward Contracts | Gain (loss) on derivative financial instruments | Reclassification out of Accumulated Other Comprehensive Income |  |  |  |  |  |
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] |  |  |  |  |  |
Cost of goods sold | $ 16 us-gaap_CostOfGoodsSold / us-gaap_DerivativeInstrumentRiskAxis = tg_ForeignCurrencyForwardContractsMember / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  | $ 0 us-gaap_CostOfGoodsSold / us-gaap_DerivativeInstrumentRiskAxis = tg_ForeignCurrencyForwardContractsMember / us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis = us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  |  |
[1] | See Notes 1, 3, 4 and 18 for more information on losses associated with plant shutdowns, asset impairments and restructurings, unusual items, gains or losses from sale of assets, gains or losses on an investment accounted for under the fair value method and other items.
[2] | This component of accumulated other comprehensive income is included in the computation of net periodic pension cost (see Note 14 for additional detail).

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