Accounts and Financing Receivables - Additional Information (Details) - Rental equipment $ in Millions	Sep. 30, 2018 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Interest rate	5.00%
Term of sales-type lease	3 years
Future minimum lease payments	$ 5.8
Future minimum lease payments of unearned income	0.2
Future minimum lease payments, 2019	2.9
Future minimum lease payments, 2020	$ 2.9

Notes receivable interest rate.

No definition available.

Name:	geos_NotesReceivableInterestRate
Namespace Prefix:	geos_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Sales type lease minimum lease payments to be received.

+ References

No definition available.

+ Details

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

- Definition

Sales type lease minimum lease payments to be received next twelve months.

+ References

No definition available.

+ Details

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

- Definition

Sales type lease minimum lease payments to be received of unearned income.

+ References

No definition available.

+ Details

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

- Definition

Sales type lease minimum lease payments to be received two years.

+ References

No definition available.

+ Details

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

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

- Definition

Term of lessor's sales-type lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888428&loc=SL77919359-209981

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	srt_ProductOrServiceAxis=geos_ManufacturedRentalEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: