Acquisitions (Details Textual) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Business acquisition contingent consideration, other long term liability	$ 0	$ 2.4
Business acquisition contingent consideration, accounts payable	$ 4.7	$ 2.7

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