Date of expiry of operating lease.

No definition available.

Name:	genc_DateOfExpiryOfOperatingLease
Namespace Prefix:	genc_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Lessee operating lease lease right of use asset.

+ References

No definition available.

+ Details

Name:	genc_LesseeOperatingLeaseLeaseRightOfUseAsset
Namespace Prefix:	genc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147478964/842-20-50-3

+ Details

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

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147478964/842-20-50-3

+ Details

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of operating lease expense. Excludes sublease income.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479041/842-20-45-4

+ Details

Name:	us-gaap_OperatingLeaseExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 5
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479041/842-20-45-5

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (g)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147478964/842-20-50-4

+ Details

Name:	us-gaap_OperatingLeasePayments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_LeaseContractualTermAxis=genc_NewLeaseAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	genc_LeaseExtensionTermAxis=genc_LeaseTermThroughAugust312024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	genc_LeaseExtensionTermAxis=genc_LeaseTermThroughAugust312025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=genc_BlawKnoxProductLineFromVolvoCeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Leases - Additional Information (Detail) - USD ($)		3 Months Ended		9 Months Ended
Leases - Additional Information (Detail) - USD ($)	Aug. 28, 2020	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Sep. 30, 2023
Lessee, Lease, Description [Line Items]
Operating Lease, Expense			$ 101,000		$ 315,000
Operating lease term	3 years
Operating leases paid in cash		$ 109,000	101,000	$ 328,000	344,000
New Lease Agreement [Member]
Lessee, Lease, Description [Line Items]
Assets	$ 970,000	420,000		420,000		$ 328,000
New Lease Agreement [Member] \| Lease term through August 31, 2024 [Member]
Lessee, Lease, Description [Line Items]
Assets			$ 352,000		$ 352,000
New Lease Agreement [Member] \| Lease term through August 31, 2025 [Member]
Lessee, Lease, Description [Line Items]
Assets		$ 361,000		$ 361,000
Blaw Knox Product Line From Volvo CE [Member] \| New Lease Agreement [Member]
Lessee, Lease, Description [Line Items]
Operating lease liability date of expiry	Aug. 31, 2025