Debt Instrument, Annual Amortization Rate, Amount

No definition available.

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

- Definition

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

+ References

No definition available.

+ Details

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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Equity Interest Pledge

+ References

No definition available.

+ Details

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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Repayment Of Excess Cashflow Percentage

+ References

No definition available.

+ Details

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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

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

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

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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

Name:	us-gaap_RatioOfIndebtednessToNetCapital1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Details

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Namespace Prefix:
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Balance Type:
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- Details

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Balance Type:
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- Details

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- Details

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- Details

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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_VariableRateAxis=gti_AdjustedLIBORateMember
Namespace Prefix:
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Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=gti_ABRMember
Namespace Prefix:
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Debt And Liquidity (2018 Credit Facility, Term Loan ) (Details) - 2018 Credit Agreement [Member] - USD ($)	1 Months Ended
	Feb. 28, 2021	Jun. 30, 2018	Feb. 28, 2018
Debt Instrument [Line Items]
Equity Interest Pledge			65.00%
Ratio of Indebtedness to Net Capital			4.00
Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		$ 2,250,000,000	$ 1,500,000,000
Debt Instrument, Annual Amortization Rate, Amount			$ 112,500,000
Repayment Of Excess Cashflow Percentage			75.00%
Line of Credit [Member] \| Contingent Event One [Member]
Debt Instrument [Line Items]
Repayment Of Excess Cashflow Percentage			50.00%
Line of Credit [Member] \| Contingent Event Two [Member]
Debt Instrument [Line Items]
Repayment Of Excess Cashflow Percentage			0.00%
Line of Credit [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate, Decrease Upon Achievement Of Specific Credit Ratings	0.50%	1.00%
Line of Credit [Member] \| Minimum [Member] \| Contingent Event One [Member]
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital			1.25
Line of Credit [Member] \| Maximum \| Contingent Event One [Member]
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital			1.75
Line of Credit [Member] \| Adjusted LIBO Rate
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	3.00%
Basis spread on variable rate, decrease	0.50%
Debt Instrument, Basis Spread on Variable Rate, Decrease Upon Achievement Of Specific Credit Ratings	0.25%
Line of Credit [Member] \| ABR [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%