Line of credit facility borrowing base as percent of assets.

No definition available.

Name:	geos_LineOfCreditFacilityBorrowingBaseAsPercentOfAssets
Namespace Prefix:	geos_
Data Type:	num: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:	num: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

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Date the credit facility first became available, in CCYY-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=6877327&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_LongtermDebtTypeAxis=geos_SecondAmendmentMember
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_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
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_DebtInstrumentAxis=geos_FrostBankCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_AccountsReceivableMember
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_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_NotesReceivableMember
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:

Long-Term Debt - Additional Information (Details) - USD ($)				12 Months Ended
	Nov. 22, 2019	Nov. 08, 2018	Mar. 02, 2011	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018
Second Amendment
Debt Instrument [Line Items]
Unencumbered liquid asset value			$ 10,000,000
Fourth Amendment
Debt Instrument [Line Items]
Unencumbered liquid asset value					$ 5,000,000
Minimum tangible net worth					$ 140,000,000
Fourth Amendment \| Subsequent Event
Debt Instrument [Line Items]
Unencumbered liquid asset value	$ 5,000,000
Minimum tangible net worth	140,000,000
Fifth Amendment \| Subsequent Event
Debt Instrument [Line Items]
Unencumbered liquid asset value	10,000,000
Minimum tangible net worth	$ 145,000,000
Frost Bank Credit Agreement
Debt Instrument [Line Items]
Total long-term debt outstanding				$ 0		$ 0
Line of credit borrowing capacity			$ 30,000,000
Credit agreement borrowing availability				$ 27,000,000
Frost Bank Credit Agreement \| Second Amendment
Debt Instrument [Line Items]
Credit agreement expiration date			2019-04
Frost Bank Credit Agreement \| Third Amendment
Debt Instrument [Line Items]
Credit agreement expiration date		2020-04
Frost Bank Credit Agreement \| Fifth Amendment \| Subsequent Event
Debt Instrument [Line Items]
Credit agreement expiration date	2022-04
Frost Bank Credit Agreement \| Prime Rate
Debt Instrument [Line Items]
Marginal interest rate				5.00%
Frost Bank Credit Agreement \| Certain Accounts Receivable \| Second Amendment
Debt Instrument [Line Items]
Borrowing base as percentage of assets			80.00%
Frost Bank Credit Agreement \| New Agreement
Debt Instrument [Line Items]
Credit agreement date				Mar. 02, 2011
Frost Bank Credit Agreement \| New Agreement \| Subsequent Event
Debt Instrument [Line Items]
Credit agreement date	Nov. 30, 2019
Frost Bank Credit Agreement \| Certain Notes Receivable \| Second Amendment
Debt Instrument [Line Items]
Borrowing base as percentage of assets			50.00%
Maximum amount of borrowing based upon assets			$ 10,000,000
Frost Bank Credit Agreement \| Certain Inventories \| Second Amendment
Debt Instrument [Line Items]
Borrowing base as percentage of assets			25.00%
Maximum amount of borrowing based upon assets			$ 20,000,000