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Gain on Dispositions of Plant, Equipment and Timberlands - Summary for Sale of Timberlands and Other Assets (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Property, Plant and Equipment [Line Items] |  |  |
Proceeds | $ 1,947 | $ 10,272 | $ 4,491
Gain | 1,726 | 9,815 | 3,950
Timberlands [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Acres | 876 | 4,830 | 942
Proceeds | 1,445 | 9,494 | 3,821
Gain | 1,410 | 9,203 | 3,590
Other [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Acres |  |  |
Proceeds | 502 | 778 | 670
Gain | $ 316 | $ 612 | $ 360

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- Definition Area of timberland. + References No definition available. + Details
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Namespace Prefix: | glt_
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Balance Type: | na
Period Type: | duration

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- Definition Amount of gain (loss) on sale or disposal of property, plant and equipment assets, including oil and gas property and timber property. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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Period Type: | duration

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Revenue from sale of timber, mill lumber, wood, and other wood products. + 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(a)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 + Details
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Balance Type: | credit
Period Type: | duration