Aggregate Principal Redemption Percentage

No definition available.

Name:	gti_AggregatePrincipalRedemptionPercentagePricePriorToNovember152015
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- Definition

Line of Credit Facility, Covenant Terms, Minimum Cash Interest Coverage Ratio

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Line of Credit Facility, Covenant Terms, Range of Maximum Senior Secured Leverage Ratio, Maximum

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Line of Credit Facility, Covenant Terms, Range of Maximum Senior Secured Leverage Ratio, Minimum

+ References

No definition available.

+ Details

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- Definition

Redemption Price Percentage Of Principal Prior To November 15, 2015

+ References

No definition available.

+ Details

Name:	gti_RedemptionPricePercentageOfPrincipalPriorToNovember152015
Namespace Prefix:	gti_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Redemption Price Percentage Of Principal

+ References

No definition available.

+ Details

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Namespace Prefix:	gti_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Repurchase Percentage Price Of Aggregate Principal Due To Change In Control

+ References

No definition available.

+ Details

Name:	gti_RepurchasePercentagePriceOfAggregatePrincipalDueToChangeInControl
Namespace Prefix:	gti_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Unpaid Indebtness After Maturity Or Acceleration

+ References

No definition available.

+ Details

Name:	gti_UnpaidIndebtnessAfterMaturityOrAcceleration
Namespace Prefix:	gti_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Unpaid Judgment Or Decree

+ References

No definition available.

+ Details

Name:	gti_UnpaidJudgmentOrDecree
Namespace Prefix:	gti_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

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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 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

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

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

- Details

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

- Definition

Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

+ 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(b))

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

+ Details

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

- 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

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of long-term debt, after unamortized discount or premium, scheduled to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ 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 210.5-02.19,20)

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

+ Details

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

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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

- Definition

The fair value of notes issued in noncash investing and financing activities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

+ Details

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

- Definition

Carrying value as of the balance sheet date of the portion of long-term debt not otherwise specified in the taxonomy that is scheduled to be repaid within one year or the normal operating cycle, if longer.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20

-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 210.5-02.19)

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

+ Details

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

- Definition

Stated interest rate of the subordinated debt.

+ References

No definition available.

+ Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gti_AmendedandRestatedCreditAgreementFebruary2015Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
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Balance Type:
Period Type:

- Details

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Debt And Liquidity (Narrative) (Details) (USD $)	3 Months Ended	0 Months Ended
Debt And Liquidity (Narrative) (Details) (USD $)	Mar. 31, 2015	Nov. 30, 2010	Feb. 27, 2015	Dec. 31, 2014	Nov. 20, 2012
Debt Instrument [Line Items]
Fair value of debt	$ 459,800,000us-gaap_LongTermDebtFairValue			$ 473,300,000us-gaap_LongTermDebtFairValue
Book value of debt	527,800,000us-gaap_OtherLongTermDebtCurrent			529,700,000us-gaap_OtherLongTermDebtCurrent
Stated interest rate				6.375%
Interest rate used to record at present value	7.00%
Loan balance, net of unamortized discount	191,446,000us-gaap_LongTermDebtCurrent			188,104,000us-gaap_LongTermDebtCurrent
Senior Notes
Debt Instrument [Line Items]
Principal amount issued					300,000,000
Stated interest rate					6.375%
Redemption price, percentage of principal, prior to November 15, 2016					100.00%
Redemption price, percentage of principal, prior to November 15, 2015					106.375%
Repurchase price, percentage of principal, due to change in control					101.00%
Senior Notes \| Minimum
Debt Instrument [Line Items]
Unpaid indebtedness or accelerated proceeds exceeds	50,000,000
Unpaid judgment or decree in excess of	50,000,000
Senior Notes \| Maximum
Debt Instrument [Line Items]
Percentage of principal allowed to redeem					35.00%
Senior Subordinated Notes
Debt Instrument [Line Items]
Face amount of debt issued in connection with acquisition		200,000,000
Interest rate used to record at present value		7.00%
Amended and Restated Credit Agreement
Debt Instrument [Line Items]
Unused borrowing capacity	329,000,000
Outstanding letters of credit	5,400,000
Minimum cash interest coverage ratio			2.50
Range of maximum senior secured leverage ratio, minimum			3.75
Range of maximum senior secured leverage ratio, maximum			3.00
Amended and Restated Credit Agreement \| Minimum
Debt Instrument [Line Items]
Undrawn commitment fee			0.35%
Amended and Restated Credit Agreement \| Maximum
Debt Instrument [Line Items]
Undrawn commitment fee			0.50%
Amended and Restated Credit Agreement \| LIBOR \| Minimum
Debt Instrument [Line Items]
Margin spread on variable interest rate			2.25%
Amended and Restated Credit Agreement \| LIBOR \| Maximum
Debt Instrument [Line Items]
Margin spread on variable interest rate			3.75%
Term Loan Facility \| Amended and Restated Credit Agreement
Debt Instrument [Line Items]
Borrowing capacity			40,000,000
Revolving Credit Facility \| Amended and Restated Credit Agreement
Debt Instrument [Line Items]
Borrowing capacity			400,000,000