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Commitments, Contingencies and Legal Proceedings - Additional Information (Detail) (USD $) | 0 Months Ended | 12 Months Ended | 0 Months Ended | 1 Months Ended
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Oct. 14, 2014 | Dec. 31, 2014 Operable_Unit | Sep. 25, 2014 | Jan. 31, 2008
Commitments Contingencies And Litigation [Line Items] |  |  |  |
Annual payments due under operating leases |  | $ 14,000,000 us-gaap_OperatingLeasesFutureMinimumPaymentsDue |  |
Aggregate contractual obligation |  | 97,000,000 glt_ContractualObligationsFutureMinimumPaymentsDue |  |
Number of operable units |  | 5 glt_NumberOfOperableUnits |  |
Upper end estimate of total past and future response costs | 1,100,000,000 us-gaap_SiteContingencyLossExposureNotAccruedHighEstimate |  |  |
Uncertainty premium for future response costs | 100,000,000 glt_UncertaintyPremiumForFutureResponseCosts |  |  |
Initial minimum amount of NRD assessment |  | 176,000,000 glt_NaturalResourceDamageLossContingencyRangeOfPossibleLossMinimum |  |
Initial maximum amount of NRD assessment |  | 333,000,000 glt_NaturalResourceDamageLossContingencyRangeOfPossibleLossMaximum |  |
Revised minimum amount of NRD assessment |  | 287,000,000 glt_NaturalResourceDamageLossContingencyRangeOfPossibleLossMinimumRevised |  |
Revised maximum amount of NRD assessment |  | 423,000,000 glt_NaturalResourceDamageLossContingencyRangeOfPossibleLossMaximumRevised |  |
Reserve for environmental liability, expected compensation payments | 45,900,000 us-gaap_AccrualForEnvironmentalLossContingenciesPayments |  |  |
Environmental loss contingencies recovered | 105,000,000 us-gaap_AccrualForEnvironmentalLossContingencies | 16,300,000 us-gaap_AccrualForEnvironmentalLossContingencies |  |
Other prepaid loss contingencies for earlier settlements | 59,000,000 glt_OtherPrepaidAccrualForEnvironmentalLossContingencies |  |  |
Cost of response incurred by government |  | 4,280,000 glt_CostReimbursementDueToUsFromAnotherPotentiallyResponsibleParties |  |
Reserve for Environmental liabilities, current portion |  | 1,100,000 glt_AccrualForEnvironmentalLossContingenciesCurrent |  |
Maximum estimated percentage of discharge |  | 27.00%glt_MaximumEstimatedPercentageOfDischarge |  |
Maximum estimated cost related to Fox River matter |  | 185,000,000 glt_MaximumEstimatedCost |  |
Maximum [Member] |  |  |  |
Commitments Contingencies And Litigation [Line Items] |  |  |  |
Period over which estimated cost to be incurred |  | 3 years |  |
Minimum [Member] |  |  |  |
Commitments Contingencies And Litigation [Line Items] |  |  |  |
Period over which estimated cost to be incurred |  | 2 years |  |
OU1 [Member] |  |  |  |
Commitments Contingencies And Litigation [Line Items] |  |  |  |
Estimated future cost of work yet to be done | 100,000,000 glt_EstimatedFutureCostOfWorkAsPartOfResponseAction / us-gaap_LitigationCaseAxis = glt_UpstreamMember |  |  |
OU2-5 [Member] |  |  |  |
Commitments Contingencies And Litigation [Line Items] |  |  |  |
Estimated future cost of work yet to be done | 500,000,000 glt_EstimatedFutureCostOfWorkAsPartOfResponseAction / us-gaap_LitigationCaseAxis = glt_DownstreamMember |  |  |
Annual estimated cost rate seek by Government |  | 70,000,000 glt_EstimatedAnnualCostOfWorkToBePerformed / us-gaap_LitigationCaseAxis = glt_DownstreamMember |  |
NCR costs and damages percentage |  |  | 100.00%glt_CostsAndDamagesPercentage / us-gaap_LitigationCaseAxis = glt_DownstreamMember |
OU2-5 [Member] | Whiting Litigation [Member] |  |  |  |
Commitments Contingencies And Litigation [Line Items] |  |  |  |
NCR costs and damages percentage |  |  |  | 100.00%glt_CostsAndDamagesPercentage / us-gaap_LitigationCaseAxis = glt_DownstreamMember / us-gaap_LitigationStatusAxis = glt_WhitingLitigationMember
Dredging Season [Member] |  |  |  |
Commitments Contingencies And Litigation [Line Items] |  |  |  |
Annual estimated cost rate seek by Government |  | $ 90,000,000 glt_EstimatedAnnualCostOfWorkToBePerformed / us-gaap_LitigationCaseAxis = glt_DredgingSeasonMember |  |

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