Commitments, Guarantees, and Contingencies (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014
Commitments And Contingencies [Line Items]
2015	$ 7,891
2016	6,249
2017	5,119
2018	3,263
2019	2,322
Thereafter	12,371
Total	37,215
Real Property [Member]
Commitments And Contingencies [Line Items]
2015	6,576
2016	5,663
2017	4,921
2018	3,246
2019	2,320
Thereafter	12,370
Total	35,096
Machinery and Equipment [Member]
Commitments And Contingencies [Line Items]
2015	1,315
2016	586
2017	198
2018	17
2019	2
Thereafter	1
Total	$ 2,119

Name:	gpx_CommitmentsAndContingenciesLineItems
Namespace Prefix:	gpx_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 10

-Section 55

-Paragraph 40

-Subparagraph (Note 3)

-URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of required minimum rental payments maturing in the next fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of required minimum rental payments maturing in the fifth fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of required minimum rental payments maturing in the forth fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of required minimum rental payments maturing in the third fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of required minimum rental payments maturing in the second fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of required minimum rental payments maturing after the fifth fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_MajorPropertyClassAxis=gpx_RealPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorPropertyClassAxis=us-gaap_MachineryAndEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: