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

Debt Instrument Loan Agreement Number

+ References

No definition available.

+ Details

Name:	glt_DebtInstrumentLoanAgreementNumber
Namespace Prefix:	glt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument number of installment payment.

+ References

No definition available.

+ Details

Name:	glt_DebtInstrumentNumberOfInstallmentPayment
Namespace Prefix:	glt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Ratio of EBITDA over net debt.

+ References

No definition available.

+ Details

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

- Definition

Loan repayable installments end date.

+ References

No definition available.

+ Details

Name:	glt_LoanRepayableInstallmentsEndDate
Namespace Prefix:	glt_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Loan repayable installments start date.

+ References

No definition available.

+ Details

Name:	glt_LoanRepayableInstallmentsStartDate
Namespace Prefix:	glt_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Margin over Euro-rate.

+ References

No definition available.

+ Details

Name:	glt_MarginOverEuroRate
Namespace Prefix:	glt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
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 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: 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

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
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 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 50

-Paragraph 3

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentFrequencyOfPeriodicPayment
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 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

- 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 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)(2))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 50

-Paragraph 3

-Subparagraph e

-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentRedemptionDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
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

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
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

+ Details

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

Long-Term Debt - Additional Information (Detail)	0 Months Ended			3 Months Ended				3 Months Ended							3 Months Ended			3 Months Ended			3 Months Ended
Long-Term Debt - Additional Information (Detail)	Mar. 31, 2015	Mar. 31, 2015	Mar. 31, 2015 Other Assets [Member] USD ($)	Mar. 31, 2015 Maximum [Member]	Mar. 31, 2015 Federal Funds Rate [Member]	Mar. 31, 2015 Revolving Credit Facility [Member]	Mar. 12, 2015 Revolving Credit Facility [Member] USD ($)	Mar. 31, 2015 Revolving Credit Facility, Due Nov. 2016 [Member]	Mar. 31, 2015 Revolving Credit Facility, Due Nov. 2016 [Member] Minimum [Member]	Mar. 31, 2015 Revolving Credit Facility, Due Nov. 2016 [Member] Maximum [Member]	Mar. 31, 2015 Revolving Credit Facility, Due Nov. 2016 [Member] Daily Euro Rate [Member] Minimum [Member]	Mar. 31, 2015 Revolving Credit Facility, Due Nov. 2016 [Member] Daily Euro Rate [Member] Maximum [Member]	Mar. 31, 2015 Letters of Credit [Member] USD ($)	Dec. 31, 2014 Letters of Credit [Member] USD ($)	Mar. 31, 2015 IKB Loan [Member] DebtAgreements Installment	Apr. 11, 2013 IKB Loan [Member] USD ($)	Apr. 11, 2013 IKB Loan [Member] EUR (€)	Mar. 31, 2015 2014 IKB Loan [Member] Installment	Sep. 04, 2014 2014 IKB Loan [Member] USD ($)	Sep. 04, 2014 2014 IKB Loan [Member] EUR (€)	Mar. 31, 2015 5.375% Notes [Member]	Oct. 03, 2012 5.375% Notes [Member] USD ($)
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity							$ 400,000,000
Debt instrument maturity date						Mar. 12, 2020		Nov. 30, 2016													Oct. 15, 2020
Federal fund rate spread					0.50%				0.125%	1.00%	1.125%	2.00%
Margin over Euro-rate		1.00%glt_MarginOverEuroRate
Leverage ratio	1.9glt_LeverageRatio			3.5
Aggregate principal amount																57,600,000	42,700,000		12,600,000	10,000,000		250,000,000
Percentage of aggregate principal amount of outstanding															2.05%			2.40%			5.375%	5.375%
Frequency of interest payable																		Quarterly			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.
Number of separate loan agreement															2
Number of installments															32			27
Installments beginning date															Jun. 30, 2015			Sep. 30, 2015
Installments ending date															Mar. 31, 2023			Jun. 30, 2022
Aggregated unamortized deferred debt issuance costs			6,100,000
Letters of credit issued													5,400,000	5,300,000
Letters of credit outstanding													$ 0