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Accrued Expenses and Other Current Liabilities - Additional Information (Details)	12 Months Ended
	Sep. 30, 2019 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