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

Operating lease rental expenses one.

+ References

No definition available.

+ Details

Name:	genc_OperatingLeaseRentalExpensesOne
Namespace Prefix:	genc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918673-209980

+ 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 4
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123391704&loc=SL77918638-209977

+ 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 5
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=123391704&loc=SL77918643-209977

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (g)(1)
-URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918686-209980

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

Leases - Additional Information (Detail) - USD ($)		12 Months Ended
Leases - Additional Information (Detail) - USD ($)	Aug. 28, 2020	Sep. 30, 2022	Sep. 30, 2021	Oct. 09, 2020
Lessee, Lease, Description [Line Items]
Total rental expense		$ 57,000	$ 78,000
Operating Lease, Expense		425,000	440,000
Operating lease term	3 years
Operating leases paid in cash		396,000	468,000
New Lease Agreement [Member]
Lessee, Lease, Description [Line Items]
Assets	$ 970,000	$ 396,000	$ 785,000	$ 254,000
Blaw Knox Product Line From Volvo CE [Member] \| New Lease Agreement [Member]
Lessee, Lease, Description [Line Items]
Operating lease term				1 year
Operating lease liability date of expiry	Aug. 31, 2023