Segment Information - Schedule of Financial and Other Information by Business Unit (Detail) (USD $)	3 Months Ended
Mar. 31, 2015 T	Mar. 31, 2014 T
Segment Reporting Information [Line Items]
Net sales	$ 417,469,000us-gaap_SalesRevenueGoodsNet	$ 455,721,000us-gaap_SalesRevenueGoodsNet
Energy and related sales, net	2,068,000glt_EnergyAndRelatedSalesNet	5,262,000glt_EnergyAndRelatedSalesNet
Total revenue	419,537,000us-gaap_SalesRevenueNet	460,983,000us-gaap_SalesRevenueNet
Cost of products sold	367,429,000us-gaap_CostOfGoodsSold	405,943,000us-gaap_CostOfGoodsSold
Gross profit (loss)	52,108,000us-gaap_GrossProfit	55,040,000us-gaap_GrossProfit
SG&A	31,272,000	33,551,000
Gains on dispositions of plant, equipment and timberlands, net	(2,654,000)	(809,000)
Total operating income (loss)	23,490,000us-gaap_OperatingIncomeLoss	22,298,000us-gaap_OperatingIncomeLoss
Non-operating expense	(4,630,000)us-gaap_NonoperatingIncomeExpense	(4,540,000)us-gaap_NonoperatingIncomeExpense
Income (loss) before income taxes	18,860,000	17,758,000
Supplementary Data
Net tons sold	260,700glt_AmountOfTonsSold	267,300glt_AmountOfTonsSold
Depreciation, depletion and amortization	15,975,000	18,615,000
Capital expenditures	21,700	14,400
Composite Fibers [Member]
Segment Reporting Information [Line Items]
Net sales	135,300,000	158,600,000
Total revenue	135,300,000	158,600,000
Cost of products sold	109,000,000	126,000,000
Gross profit (loss)	26,300,000	32,600,000
SG&A	11,600,000	13,300,000
Total operating income (loss)	14,700,000	19,300,000
Income (loss) before income taxes	14,700,000	19,300,000
Supplementary Data
Net tons sold	38,000	40,000
Depreciation, depletion and amortization	6,700,000	7,600,000
Capital expenditures	5,900,000	6,000,000
Advanced Airlaid Materials [Member]
Segment Reporting Information [Line Items]
Net sales	62,300,000	71,300,000
Total revenue	62,300,000	71,300,000
Cost of products sold	55,100,000	63,100,000
Gross profit (loss)	7,200,000	8,200,000
SG&A	1,900,000	2,300,000
Total operating income (loss)	5,300,000	5,900,000
Income (loss) before income taxes	5,300,000	5,900,000
Supplementary Data
Net tons sold	24,100	25,100
Depreciation, depletion and amortization	2,200,000	2,300,000
Capital expenditures	1,300,000	1,500,000
Specialty Papers [Member]
Segment Reporting Information [Line Items]
Net sales	219,900,000	225,800,000
Energy and related sales, net	2,100,000	5,300,000
Total revenue	222,000,000	231,100,000
Cost of products sold	200,400,000	215,000,000
Gross profit (loss)	21,600,000	16,100,000
SG&A	12,100,000	13,700,000
Total operating income (loss)	9,500,000	2,400,000
Income (loss) before income taxes	9,500,000	2,400,000
Supplementary Data
Net tons sold	198,700	202,200
Depreciation, depletion and amortization	6,600,000	8,300,000
Capital expenditures	13,200,000	6,200,000
Other and Unallocated [Member]
Segment Reporting Information [Line Items]
Cost of products sold	2,900,000	1,800,000
Gross profit (loss)	(2,900,000)	(1,800,000)
SG&A	5,600,000	4,300,000
Gains on dispositions of plant, equipment and timberlands, net	(2,700,000)	(800,000)
Total operating income (loss)	(5,800,000)	(5,200,000)
Non-operating expense	(4,600,000)	(4,500,000)
Income (loss) before income taxes	(10,400,000)	(9,800,000)
Supplementary Data
Depreciation, depletion and amortization	500,000	500,000
Capital expenditures	$ 1,300,000	$ 800,000

Amount of tons sold.

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Revenue from sales of excess internally generated power, net of costs to produce, and revenue from sales of renewable energy credits.

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Total costs related to goods produced and sold during the reporting period.

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The aggregate total costs related to selling a firm's product and services, as well as all other general and administrative expenses. Direct selling expenses (for example, credit, warranty, and advertising) are expenses that can be directly linked to the sale of specific products. Indirect selling expenses are expenses that cannot be directly linked to the sale of specific products, for example telephone expenses, Internet, and postal charges. General and administrative expenses include salaries of non-sales personnel, rent, utilities, communication, etc.

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