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Shareholders' Equity - Additional Information (Detail)	12 Months Ended
	Sep. 30, 2015
Common Stock [Member]
Class of Stock [Line Items]
Right of holders to elect company's board of directors	25.00%
Class B Stock [Member]
Class of Stock [Line Items]
Right of holders to elect company's board of directors	75.00%

X

- Definition

Right of holders to elect company's board of directors.

+ References

No definition available.

+ Details

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Namespace Prefix:	genc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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

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

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=genc_CommonClassUndefinedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: