Name:	gpx_RevenuePerformanceObligationExpectingTimingofSatisfactionPercentageExpectedtobeRecognizedWithin12Months
Namespace Prefix:	gpx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Revenue from Contract with Customer, Collection Period

No definition available.

Name:	gpx_RevenuefromContractwithCustomerCollectionPeriod
Namespace Prefix:	gpx_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Revenue from Contract with Customer, Percentage of Revenues Derived From Other Sources

No definition available.

Name:	gpx_RevenuefromContractwithCustomerPercentageofRevenuesDerivedFromOtherSources
Namespace Prefix:	gpx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Revenue from Contract with Customer, Percentage of Revenues Derived From Services Provided

No definition available.

Name:	gpx_RevenuefromContractwithCustomerPercentageofRevenuesDerivedFromServicesProvided
Namespace Prefix:	gpx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in estimate of transaction price which increases (decreases) right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time. Includes, but is not limited to, change in assessment of whether estimate of variable consideration is constrained.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130551-203045

Name:	us-gaap_ContractWithCustomerAssetCumulativeCatchUpAdjustmentToRevenueChangeInEstimateOfTransactionPrice
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

Name:	us-gaap_ContractWithCustomerLiabilityRevenueRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_DisaggregationOfRevenueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

Name:	us-gaap_RevenueFromContractWithCustomerAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130556-203045