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Leases - Supplemental Cash Flow Information Related to Operating Lease (Details) $ in Thousands | 12 Months Ended
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Sep. 30, 2020 USD ($)
Leases [Abstract] |
Cash paid for amounts included in the measurement of lease liability | $ 165
Right-of-use asset established upon adoption of ASC 842 | $ 219

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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

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- Definition Amount of increase in right-of-use asset obtained in exchange for operating lease liability. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 55 -Paragraph 53 -URI http://asc.fasb.org/extlink&oid=121568110&loc=SL77918982-209971 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(2) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980 + Details
Name: | us-gaap_RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration