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Stock-Based Compensation - Additional Information (Detail) | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Restricted Stock Units (RSU) [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
The vesting graded scale | The RSUs vest on the passage of time, generally on a graded scale over a three, four, and five-year period, or in certain instances the RSUs were issued with five year cliff vesting. |
Performance Share Awards (PSAs) [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Cumulative performance targets | 3 years |
Grants under performance share awards | 100,801 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = glt_PerformanceShareAwardsMember | 90,791 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = glt_PerformanceShareAwardsMember
Stock Only Stock Appreciation Rights (SOSARs) [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Vesting period of stock | 3 years |
Vesting term | 10 years |

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- Definition Share based compensation arrangement by share based payment award equity instruments other than options cumulative performance target period. + References No definition available. + Details
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- Definition Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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