Aggregate Principal Redemption Percentage

No definition available.

Name:	gti_AggregatePrincipalRedemptionPercentagePricePriorToNovember152015
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Period Type:	instant

- Definition

Maximum Leverage Ratio High End

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Maximum Leverage Ratio Low End

+ References

No definition available.

+ Details

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

- Definition

Minimum Interest Coverage Ratio High End

+ References

No definition available.

+ Details

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

- Definition

Minimum Interest Coverage Ratio Low End

+ References

No definition available.

+ Details

Name:	gti_MinimumInterestCoverageRatioLowEnd
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Balance Type:	debit
Period Type:	instant

- 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

Name:	gti_RedemptionPricePercentageOfPrincipalPriorToNovember152016
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

Revolving credit facility portion of total credit facility outstanding

+ References

No definition available.

+ Details

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

- Definition

Term loan portion of revolving credit facility balance

+ References

No definition available.

+ Details

Name:	gti_TermLoanBalance
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

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-Name Accounting Standards Codification
-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

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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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

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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

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

- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. 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 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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-Name Accounting Standards Codification
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-SubTopic 10
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-Paragraph 1
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20, 22
-Article 5

+ Details

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

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

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- Details

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- Details

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- Details

Name:	us-gaap_DebtInstrumentAxis=gti_AmendedandRestatedCreditAgreementFebruary2015Member
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- Details

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- Details

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Debt And Liquidity (Narrative) (Details) - USD ($)	Feb. 27, 2015	Mar. 31, 2016	Dec. 31, 2015	Jul. 28, 2015	Apr. 23, 2014	Nov. 20, 2012
Debt Instrument [Line Items]
Fair value of debt		$ 277,400,000
Long-term Debt		369,817,000	$ 367,227,000
Term Loan Balance		38,000,000
Minimum Interest Coverage Ratio Low End		1.50
Minimum Interest Coverage Ratio High End		2.50
Maximum Leverage Ratio High End		5.75
Maximum Leverage Ratio Low End		3.00
Revolving Credit Facility Balance		61,000,000
Stated interest rate			6.375%
Loan balance, net of unamortized discount		9,779,000	$ 4,772,000
Senior Notes
Debt Instrument [Line Items]
Long-term Debt		269,390,000	$ 267,827,000
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%
Amended and Restated Credit Agreement
Debt Instrument [Line Items]
Unused borrowing capacity		90,000,000
Outstanding letters of credit		$ 8,100,000
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	0.70%
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	4.75%
Term Loan Facility \| Amended and Restated Credit Agreement
Debt Instrument [Line Items]
Borrowing capacity	$ 40,000,000
Term Loan Facility \| Amended and Restated Credit Agreement July 2015 [Member]
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
Revolving Credit Facility \| Amended and Restated Credit Agreement July 2015 [Member]
Debt Instrument [Line Items]
Borrowing capacity				$ 375,000,000