Deferred Revenue and Other Liabilities - Additional Information (Details)	12 Months Ended
Sep. 30, 2020 USD ($)
Deferred Credits And Other Liabilities [Abstract]
Purchased stop-loss coverage for individual claims	$ 175,000

Minimum amount per claimant on which company purchased stop loss.

No definition available.

Name:	geos_MinimumAmountPerClaimantOnWhichCompanyPurchasedStopLoss
Namespace Prefix:	geos_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration