Inventories - Additional Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Inventory Disclosure [Abstract]
Inventories transferred to rental equipment	$ 0.1	$ 2.8

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