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Summary of Significant Accounting Policies - Scedhule of Translation of Foreign Currencies Exchange Rates (Parentheticals) (Details)	Jun. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Scedhule of Translation of Foreign Currencies Exchange Rates [Line Items]
Translation of foreign currencies	1
USD [Member]
Scedhule of Translation of Foreign Currencies Exchange Rates [Line Items]
Translation of foreign currencies		1	1
Year-Average Rate [Member]
Scedhule of Translation of Foreign Currencies Exchange Rates [Line Items]
Translation of foreign currencies		1	1

X

- Definition

Foreign exchange rate used to translate amounts denominated in functional currency to reporting currency.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481674/830-30-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
-SubTopic 30
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479424/830-30-S99-1

+ Details

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

X

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

X

- Details

Name:	srt_CurrencyAxis=currency_USD
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_IntercompanyForeignCurrencyBalanceByDescriptionAxis=gti_YearAverageRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: