Funded ratio debt to EBITDA.

No definition available.

Name:	geos_FundedRatioDebtToEBITDA
Namespace Prefix:	geos_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Line of credit facility borrowing base as percent of assets.

+ References

No definition available.

+ Details

Name:	geos_LineOfCreditFacilityBorrowingBaseAsPercentOfAssets
Namespace Prefix:	geos_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line of credit facility expiration date.

+ References

No definition available.

+ Details

Name:	geos_LineOfCreditFacilityExpirationDate
Namespace Prefix:	geos_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum amount of line of credit facility borrowing based upon assets.

+ References

No definition available.

+ Details

Name:	geos_MaximumAmountOfLineOfCreditFacilityBorrowingBasedUponAssets
Namespace Prefix:	geos_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Minimum tangible net worth.

+ References

No definition available.

+ Details

Name:	geos_MinimumTangibleNetWorth
Namespace Prefix:	geos_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Unencumbered liquid asset value.

+ References

No definition available.

+ Details

Name:	geos_UnencumberedLiquidAssetValue
Namespace Prefix:	geos_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the credit facility first became available, in YYYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInitiationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the noncurrent portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=99376301&loc=d3e1336-112600

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=99376301&loc=d3e1314-112600

+ Details

Name:	us-gaap_LongTermLineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_PrimeRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=geos_FourthAmendmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=geos_FifthAmendmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_NotesReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=geos_SixthAmendmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=us-gaap_InventoriesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=geos_FrostBankCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=geos_SecondAmendmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=geos_ThirdAmendmentMember
Namespace Prefix:
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Period Type:

Long-Term Debt - Additional Information (Details)		1 Months Ended	3 Months Ended	12 Months Ended
Long-Term Debt - Additional Information (Details)	Mar. 02, 2011 USD ($)	Nov. 30, 2019 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
Prime Rate
Debt Instrument [Line Items]
Marginal interest rate				3.25%
Fourth Amendment
Debt Instrument [Line Items]
Unencumbered liquid asset value		$ 5,000,000
Minimum tangible net worth		140,000,000
Fifth Amendment
Debt Instrument [Line Items]
Unencumbered liquid asset value		10,000,000
Minimum tangible net worth		$ 145,000,000
Fifth Amendment \| Eligible Accounts
Debt Instrument [Line Items]
Maximum amount of borrowing based upon assets	$ 10,000,000
Sixth Amendment \| Eligible Inventory
Debt Instrument [Line Items]
Maximum amount of borrowing based upon assets	$ 20,000,000
Frost Bank Credit Agreement
Debt Instrument [Line Items]
Total long-term debt outstanding				$ 0	$ 0
Frost Bank Credit Agreement \| New Agreement
Debt Instrument [Line Items]
Credit agreement date				Mar. 02, 2011
Frost Bank Credit Agreement \| Second Amendment
Debt Instrument [Line Items]
Credit agreement expiration date	2020-04
Borrowing base as percentage of assets	80.00%
Frost Bank Credit Agreement \| Third Amendment
Debt Instrument [Line Items]
Credit agreement expiration date		2022-04
Frost Bank Credit Agreement \| Fourth Amendment
Debt Instrument [Line Items]
Maximum amount of available borrowing			$ 30,000,000
Frost Bank Credit Agreement \| Fifth Amendment
Debt Instrument [Line Items]
Minimum tangible net worth			145,000,000
Maximum amount of available borrowing			$ 20,000,000
Funded ratio debt to EBITDA			1.50
Frost Bank Credit Agreement \| Fifth Amendment \| Eligible Accounts
Debt Instrument [Line Items]
Maximum amount of borrowing based upon assets			$ 20,000,000
Borrowing base as percentage of assets	50.00%
Frost Bank Credit Agreement \| Sixth Amendment
Debt Instrument [Line Items]
Minimum tangible net worth			$ 132,000,000
Funded ratio debt to EBITDA			1.00
Frost Bank Credit Agreement \| Sixth Amendment \| Eligible Inventory
Debt Instrument [Line Items]
Maximum amount of borrowing based upon assets			$ 15,000,000
Borrowing base as percentage of assets	25.00%