Amount of letters of credit issued and reducing availability under revolving credit facility.

No definition available.

Name:	glt_AmountOfLettersOfCreditIssuedAndReducingAvailabilityUnderRevolvingCreditFacility
Namespace Prefix:	glt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Leverage ratio.

+ References

No definition available.

+ Details

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Namespace Prefix:	glt_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

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-Publisher FASB
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-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
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-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: 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

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: 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)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of debt redemption features under terms of the debt agreement.

+ References

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The periodic charge to earnings for amortization of deferred issuance costs associated with an own-share lending arrangement during the term of the arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 2A
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=7656903&loc=SL6757479-112611

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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Balance Type:
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Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_EurodollarMember
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Data Type:	na
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Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
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Data Type:	na
Balance Type:
Period Type:

- Details

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Long-Term Debt - Additional Information (Detail)	12 Months Ended
Long-Term Debt - Additional Information (Detail)	Dec. 31, 2015 USD ($)	Mar. 12, 2015 USD ($)	Dec. 31, 2014 USD ($)	Oct. 03, 2012 USD ($)
Debt Instrument [Line Items]
Leverage ratio	1.6
Amortization expense related to deferred debt issuance costs	$ 1,200,000
Other Assets [Member]
Debt Instrument [Line Items]
Unamortized deferred debt issuance costs	$ 5,400,000
Maximum [Member]
Debt Instrument [Line Items]
Leverage ratio	3.5
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 400,000,000
Long-term debt, maturity date	Mar. 12, 2020
Federal fund rate spread	1.00%
Revolving Credit Facility [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Federal fund rate spread	0.125%
Revolving Credit Facility [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Federal fund rate spread	1.00%
Revolving Credit Facility [Member] \| Federal Funds Rate [Member]
Debt Instrument [Line Items]
Federal fund rate spread	0.50%
Revolving Credit Facility [Member] \| Daily Euro Rate [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Federal fund rate spread	1.125%
Revolving Credit Facility [Member] \| Daily Euro Rate [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Federal fund rate spread	2.00%
Letters of Credit [Member]
Debt Instrument [Line Items]
Letters of credit issued	$ 5,300,000		$ 5,300,000
Letters of credit outstanding	$ 0
5.375% Notes [Member]
Debt Instrument [Line Items]
Long-term debt, maturity date	Oct. 15, 2020
Aggregate principal amount				$ 250,000,000
Percentage of aggregate principal amount of outstanding	5.375%			5.375%
Frequency of interest payable	Semiannually
Debt instrument redemption	The 5.375% Notes are redeemable, in whole or in part, at anytime on or after October 15, 2016 at the redemption prices specified in the applicable Indenture. Prior to October 15, 2016, we may redeem some or all of the Notes at a "make-whole" premium as specified in the Indenture.