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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Period Type:	instant

- Definition

Debt Instrument, Amortization Rate

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument Prepayment Premium

+ References

No definition available.

+ Details

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

- Definition

Equity Interest Pledge

+ References

No definition available.

+ Details

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

- Definition

Excess Cashflow Threshold Percentage

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Line of credit upfront fee percentage

+ References

No definition available.

+ Details

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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

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Namespace Prefix:	us-gaap_
Data Type:	num: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

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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=75038535&loc=d3e64711-112823

+ Details

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

- Definition

Fair value amount of debt instrument that was repurchased.

+ References

No definition available.

+ Details

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

- Definition

Carrying value as of the balance sheet date of dividends declared but unpaid on equity securities issued by the entity and outstanding.

+ 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(24))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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-Name Accounting Standards Codification
-Topic 942
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 944
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-Paragraph 1
-Subparagraph (SX 210.7-03(a)(15)(5))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

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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

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

- 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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585

+ Details

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Period Type:	duration

- Details

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- Details

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- Details

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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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- Details

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- Details

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- Details

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- Details

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Debt And Liquidity (2018 Credit Agreement) (Details) - USD ($)					12 Months Ended
	Dec. 22, 2020	Dec. 20, 2019	Feb. 13, 2019	Feb. 12, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 15, 2018	Apr. 19, 2018
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Equity Interest Pledge				65.00%
Dividends Payable									$ 160,000,000
Repayments of Secured Debt					$ 896,214,000	$ 350,140,000	$ 56,372,000
Debt Instrument, Repurchase Amount					$ 80,000,000
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage					101.594%
2018 Term Loan Facility [Member]
Debt Instrument [Line Items]
Repayments of Secured Debt		$ 225,000,000	$ 125,000,000		$ 820,000,000
2018 Credit Agreement [Member]
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital				4.00
Brookfield Promissory Note [Member] \| Brookfield [Member]
Debt Instrument [Line Items]
Dividends Payable									$ 750,000,000
Line of Credit [Member] \| 2018 Term Loan Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 1,500,000,000
Debt Instrument, Basis Spread on Variable Rate					0.25%
Debt Instrument, Amortization Rate				5.00%
Debt Instrument Prepayment Premium				1.00%
Excess Cashflow Threshold Percentage				75.00%
Line of Credit [Member] \| 2018 Term Loan Facility [Member] \| Contingent Event One [Member]
Debt Instrument [Line Items]
Excess Cashflow Threshold Percentage				50.00%
Line of Credit [Member] \| 2018 Term Loan Facility [Member] \| Contingent Event One [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital				1.25
Line of Credit [Member] \| 2018 Term Loan Facility [Member] \| Contingent Event One [Member] \| Maximum
Debt Instrument [Line Items]
Ratio of Indebtedness to Net Capital				1.75
Line of Credit [Member] \| 2018 Term Loan Facility [Member] \| Contingent Event Two [Member]
Debt Instrument [Line Items]
Excess Cashflow Threshold Percentage				0.00%
Line of Credit [Member] \| 2018 Term Loan Facility [Member] \| ABR [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				2.50%
Line of Credit [Member] \| 2018 Term Loan Facility [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				3.50%
Revolving Credit Facility [Member] \| 2018 Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 250,000,000			$ 1,500,000,000	$ 2,250,000,000
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%
Line of credit upfront fee percentage								1.00%
Revolving Credit Facility [Member] \| 2018 Revolving Credit Facility [Member] \| ABR [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				2.75%
Revolving Credit Facility [Member] \| 2018 Revolving Credit Facility [Member] \| London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate				3.75%