Accrued Expenses - Additional Information (Detail) (USD $)	12 Months Ended
Sep. 30, 2013
Payables and Accruals [Abstract]
Reduction in estimated advertising expenses for the 2014 ConExpo show	$ 750,000

Estimated reduction in advertising expenses in next year.

No definition available.

Name:	genc_EstimatedReductionInAdvertisingExpensesInNextYear
Namespace Prefix:	genc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration