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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
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   $ 14,000,000us-gaap_OperatingLeasesFutureMinimumPaymentsDue    
Aggregate contractual obligation   97,000,000glt_ContractualObligationsFutureMinimumPaymentsDue    
Number of operable units   5glt_NumberOfOperableUnits    
Upper end estimate of total past and future response costs 1,100,000,000us-gaap_SiteContingencyLossExposureNotAccruedHighEstimate      
Uncertainty premium for future response costs 100,000,000glt_UncertaintyPremiumForFutureResponseCosts      
Initial minimum amount of NRD assessment   176,000,000glt_NaturalResourceDamageLossContingencyRangeOfPossibleLossMinimum    
Initial maximum amount of NRD assessment   333,000,000glt_NaturalResourceDamageLossContingencyRangeOfPossibleLossMaximum    
Revised minimum amount of NRD assessment   287,000,000glt_NaturalResourceDamageLossContingencyRangeOfPossibleLossMinimumRevised    
Revised maximum amount of NRD assessment   423,000,000glt_NaturalResourceDamageLossContingencyRangeOfPossibleLossMaximumRevised    
Reserve for environmental liability, expected compensation payments 45,900,000us-gaap_AccrualForEnvironmentalLossContingenciesPayments      
Environmental loss contingencies recovered 105,000,000us-gaap_AccrualForEnvironmentalLossContingencies 16,300,000us-gaap_AccrualForEnvironmentalLossContingencies    
Other prepaid loss contingencies for earlier settlements 59,000,000glt_OtherPrepaidAccrualForEnvironmentalLossContingencies      
Cost of response incurred by government   4,280,000glt_CostReimbursementDueToUsFromAnotherPotentiallyResponsibleParties    
Reserve for Environmental liabilities, current portion   1,100,000glt_AccrualForEnvironmentalLossContingenciesCurrent    
Maximum estimated percentage of discharge   27.00%glt_MaximumEstimatedPercentageOfDischarge    
Maximum estimated cost related to Fox River matter   185,000,000glt_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 100,000,000glt_EstimatedFutureCostOfWorkAsPartOfResponseAction
/ us-gaap_LitigationCaseAxis
= glt_UpstreamMember		      
OU2-5 [Member]        
Commitments Contingencies And Litigation [Line Items]        
Estimated future cost of work yet to be done 500,000,000glt_EstimatedFutureCostOfWorkAsPartOfResponseAction
/ us-gaap_LitigationCaseAxis
= glt_DownstreamMember		      
Annual estimated cost rate seek by Government   70,000,000glt_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   $ 90,000,000glt_EstimatedAnnualCostOfWorkToBePerformed
/ us-gaap_LitigationCaseAxis
= glt_DredgingSeasonMember