Acquisitions (Details Textual) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Business acquisition contingent consideration, other long term liability	$ 2,467	$ 1,392
Business acquisition contingent consideration, accounts payable	$ 2,718	$ 2,405

Business acquisition contingent consideration included in other long term liability.

No definition available.

Name:	gpx_BusinessAcquisitionContingentConsiderationOtherLongTermLiability
Namespace Prefix:	gpx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant