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Stock-Based Compensation - Summary of RSU and PSA Activity (Detail) (Restricted Stock Units (RSU) and Performance Share Awards (PSAs) [Member])
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Restricted Stock Units (RSU) and Performance Share Awards (PSAs) [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Beginning Balance 1,001,814us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
847,679us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
788,088us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
Granted 178,882us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
315,196us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
209,021us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
Forfeited (47,379)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
(47,831)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
(52,800)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
Shares delivered (244,375)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
(113,230)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
(96,630)us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
Ending Balance 888,942us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
1,001,814us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember
847,679us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= glt_RestrictedStockUnitsAndPerformanceShareAwardsMember