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Energy and Related Sales, Net - Summary of Energy and Related Sales Net (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Energy And Related Sales Net [Abstract] |  |  |
Energy sales | $ 11,886 us-gaap_SalesRevenueEnergyServices | $ 8,189 us-gaap_SalesRevenueEnergyServices | $ 5,284 us-gaap_SalesRevenueEnergyServices
Costs to produce | (6,204)us-gaap_CostOfServicesEnergyServices | (6,784)us-gaap_CostOfServicesEnergyServices | (4,187)us-gaap_CostOfServicesEnergyServices
Net | 5,682 glt_SalesRevenueEnergyServicesNet | 1,405 glt_SalesRevenueEnergyServicesNet | 1,097 glt_SalesRevenueEnergyServicesNet
Renewable energy credits | 2,245 us-gaap_OtherAlternativeEnergySalesRevenue | 1,748 us-gaap_OtherAlternativeEnergySalesRevenue | 5,903 us-gaap_OtherAlternativeEnergySalesRevenue
Total | $ 7,927 glt_EnergyAndRelatedSalesNet | $ 3,153 glt_EnergyAndRelatedSalesNet | $ 7,000 glt_EnergyAndRelatedSalesNet

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- Definition Revenue from sales of excess internally generated power, net of costs to produce, and revenue from sales of renewable energy credits. + References No definition available. + Details
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- Details
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- Definition Sales revenue energy services net. + References No definition available. + Details
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- Definition Cost incurred in providing energy services during the reporting period. + References 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=26872669&loc=d3e20235-122688 + Details
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- Definition Revenue earned during the period from alternative energy sources (for example, ethanol, biomass, solar, geothermal, and wind power). + References 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=26872669&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62136-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=8451039&loc=d3e62246-109447 + Details
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- Definition 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. + References 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=26872669&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Article 5 + Details
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