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Accrued Expenses and Other Current Liabilities - Additional Information (Details) | 12 Months Ended
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Sep. 30, 2018 USD ($)
Payables And Accruals [Abstract] |
Purchased stop-loss coverage for individual claims | $ 175,000

X
- Definition Minimum amount per claimant on which company purchased stop loss. + References No definition available. + Details
Name: | geos_MinimumAmountPerClaimantOnWhichCompanyPurchasedStopLoss
Namespace Prefix: | geos_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_PayablesAndAccrualsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration