Leases - Supplemental Cash Flow Information Related to Operating Lease (Details) - USD ($) $ in Thousands	3 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liability	$ 42	$ 40

Cash paid for amounts included in measurement of lease liability.

No definition available.

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