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

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- Definition Estimated reduction in advertising expenses in next year. + References No definition available. + Details
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Namespace Prefix: | genc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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