Borrowing Threshold

No definition available.

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

- Definition

Borrowing Threshold Percentage

+ References

No definition available.

+ Details

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Namespace Prefix:	gti_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Annual Amortization Rate, Amount

+ References

No definition available.

+ Details

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Namespace Prefix:	gti_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Debt Instrument, Basis Spread on Variable Rate, Decrease Upon Achievement Of Specific Public Ratings

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Basis Spread on Variable Rate, Increase (Decrease)

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Debt Instrument, Covenant, Restricted Payments Allowable Pursuant To Certain Baskets, Pro Forma Consolidated First Lien Net Leverage Ratio, Maximum

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Covenant, Restricted Payments Allowable With No Default Or Event Of Default, Pro Forma Consolidated First Lien Net Leverage Ratio, Maximum

+ References

No definition available.

+ Details

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Namespace Prefix:	gti_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Redemption Price, Premium Applicable, Percentage

+ References

No definition available.

+ Details

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Namespace Prefix:	gti_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Variable Rate

+ References

No definition available.

+ Details

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Namespace Prefix:	gti_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Equity Interest Pledge

+ References

No definition available.

+ Details

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Namespace Prefix:	gti_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Excess Cashflow Threshold Percentage

+ References

No definition available.

+ Details

Name:	gti_ExcessCashflowThresholdPercentage
Namespace Prefix:	gti_
Data Type:	dtr-types: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

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types: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/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (a)
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+ Details

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

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=123599511&loc=d3e64711-112823

+ Details

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

- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

+ Details

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

- 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://fasb.org/us-gaap/role/ref/legacyRef
-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=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
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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Balance Type:	na
Period Type:	duration

- 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

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

- Definition

Indebtedness divided by net capital.

+ References

No definition available.

+ Details

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Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow to repay long-term debt that is wholly or partially secured by collateral. Excludes repayments of tax exempt secured debt.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3291-108585

+ Details

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

- Definition

Stated interest rate of the subordinated debt.

+ References

No definition available.

+ Details

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

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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Debt And Liquidity (Narrative) (Details)			1 Months Ended		3 Months Ended	9 Months Ended
Debt And Liquidity (Narrative) (Details)	Jan. 31, 2021	Dec. 22, 2020 USD ($)	Feb. 28, 2021	Dec. 31, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2018 USD ($)	May 31, 2018 USD ($)	Feb. 28, 2018 USD ($)
Debt Instrument [Line Items]
Repayments of Secured Debt						$ 300,000,000	$ 249,214,000
Subordinated Borrowing, Interest Rate		4.625%
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed						30.00%
2020 Senior Notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 500,000,000
Subordinated Borrowing, Interest Rate		4.625%
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed				40.00%
Debt Instrument, Redemption Price, Percentage				104.625%
Debt Instrument, Redemption Price, Premium Applicable, Percentage				100.00%
Debt Instrument, Covenant, Restricted Payments Allowable With No Default Or Event Of Default, Pro Forma Consolidated First Lien Net Leverage Ratio, Maximum				2.00
Debt Instrument, Covenant, Restricted Payments Allowable Pursuant To Certain Baskets, Pro Forma Consolidated First Lien Net Leverage Ratio, Maximum				2.00
Fair Value, Inputs, Level 3
Debt Instrument [Line Items]
Fair Value of Debt				$ 1,453,000,000	$ 1,160,000,000	$ 1,160,000,000
2018 Credit Agreement
Debt Instrument [Line Items]
Equity Interest Pledge										65.00%
Ratio of Indebtedness to Net Capital										4.00
2018 Credit Agreement \| Minimum
Debt Instrument [Line Items]
Debt Instrument, Variable Rate	1.00%		0.50%
2018 Credit Agreement \| Term Loan Facility
Debt Instrument [Line Items]
Repayments of Secured Debt				$ 500,000,000	$ 100,000,000	300,000,000
Line of Credit Facility, Maximum Borrowing Capacity								$ 2,250,000,000	$ 1,500,000,000
Debt Instrument, Annual Amortization Rate, Amount						$ 112,500,000
Excess Cashflow Threshold Percentage										75.00%
2018 Credit Agreement \| Term Loan Facility \| Contingent Event One
Debt Instrument [Line Items]
Excess Cashflow Threshold Percentage										50.00%
2018 Credit Agreement \| Term Loan Facility \| Contingent Event Two
Debt Instrument [Line Items]
Excess Cashflow Threshold Percentage										0.00%
2018 Credit Agreement \| Term Loan Facility \| Minimum \| Contingent Event One
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital										1.25
2018 Credit Agreement \| Term Loan Facility \| Maximum \| Contingent Event One
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital										1.75
2018 Credit Agreement \| Term Loan Facility \| Adjusted LIBO Rate
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			3.00%
Debt Instrument, Basis Spread on Variable Rate, Increase (Decrease)			(0.50%)
Debt Instrument, Basis Spread on Variable Rate, Decrease Upon Achievement Of Specific Public Ratings			0.25%
2018 Credit Agreement \| Term Loan Facility \| ABR
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate			2.00%
2018 Credit Agreement \| Revolving Credit Facility
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity										$ 250,000,000
Debt Instrument, Basis Spread on Variable Rate						0.25%
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage						0.25%
Borrowing Threshold										$ 35,000,000
Borrowing Threshold Percentage										35.00%
2018 Credit Agreement \| Revolving Credit Facility \| Adjusted LIBO Rate
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						3.75%
2018 Credit Agreement \| Revolving Credit Facility \| ABR
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate						2.75%