Inventories - Additional Information (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
Jun. 30, 2014	Jun. 30, 2013
Inventory, Net [Abstract]
Inventories transferred to rental equipment	$ 7.0	$ 4.7

Assets that have been manufactured by company that is transferred to fixed assets to generate rental revenue.

No definition available.

Name:	geos_InventoriesTransferredToRentalEquipment
Namespace Prefix:	geos_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration