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v2.4.1.9

Fair Value of Financial Instruments - Carrying Value and Fair Value of Long-Term Debt (Parenthetical) (Detail) | Dec. 31, 2014 | Dec. 31, 2013
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2.05% Term Loan [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Percentage of aggregate principal amount of outstanding | 2.05%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = glt_TwoPointZeroFivePercentTermLoanMember | 2.05%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = glt_TwoPointZeroFivePercentTermLoanMember
2.40% Term Loan [Member] |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Percentage of aggregate principal amount of outstanding | 2.40%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = glt_TwoPointFourZeroPercentTermLoanMember |

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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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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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- Details
Name: | us-gaap_LongtermDebtTypeAxis=glt_TwoPointFourZeroPercentTermLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_LongtermDebtTypeAxis=glt_TwoPointZeroFivePercentTermLoanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |