Name:	glt_EnergyAndRelatedSalesNet
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Energy and Related Sales, Net [Abstract]

No definition available.

Name:	glt_EnergyAndRelatedSalesNetAbstract
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Renewable energy credits sales revenue.

No definition available.

Name:	glt_RenewableEnergyCreditsSalesRevenue
Namespace Prefix:	glt_
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Sales revenue energy services net.

No definition available.

Name:	glt_SalesRevenueEnergyServicesNet
Namespace Prefix:	glt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Cost incurred in providing energy services during the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(d))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_CostOfServicesEnergyServices
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Balance Type:	debit
Period Type:	duration

Revenue derived from energy-related services such as supplying various forms of energy from the operation of on-site facilities or cogeneration plants and procurement services provided to energy purchasers.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688