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Related Party Transactions - Additional Information (Detail) (Marcar [Member], USD $) | 12 Months Ended
--- | ---
Sep. 30, 2013 | Sep. 30, 2012
Marcar [Member] |  |
Related Party Transaction [Line Items] |  |
Minimum lease payment period | 48 months |
Lease payments to Marcar | $ 138,000 | $ 151,000

X
- Definition Minimum lease payment period. + References No definition available. + Details
Name: | genc_MinimumLeasePaymentPeriod
Namespace Prefix: | genc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References No definition available. + Details
Name: | us-gaap_LeaseAndRentalExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration