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

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- Definition Cash paid for amounts included in measurement of lease liability. + References No definition available. + Details
Name: | geos_CashPaidForAmountsIncludedInMeasurementOfLeaseLiability
Namespace Prefix: | geos_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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