Name:	gpp_DistributionMadeToLimitedPartnerAndGenearlPartnerFirstQualifierPercentageDistribution
Namespace Prefix:	gpp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

No definition available.

Name:	gpp_DistributionMadeToLimitedPartnerAndGenearlPartnerThirdQualifierPercentageDistribution
Namespace Prefix:	gpp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Distribution Made To Limited Partner And Genearl Partner, Threshold In Days After End Of Each Calendar Quarter, Distribution Payment

No definition available.

Name:	gpp_DistributionMadeToLimitedPartnerAndGenearlPartnerThresholdInDaysAfterEndOfEachCalendarQuarterDistributionPayment
Namespace Prefix:	gpp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Per unit of ownership amount of annualized minimum cash distributions to be paid to unit-holder of a limited partnership (LP).

No definition available.

Name:	gpp_DistributionMadeToLimitedPartnerAndGeneralPartnerAnnualizedMinimumDistributionsToBePaidPerUnit
Namespace Prefix:	gpp_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

Distribution made to limited partner and general partner, second qualifier percentage distribution until the partnership distributes an amount equal to any arrearages of the minimum quarterly distribution for any prior quarters on each outstanding common unit.

No definition available.

Name:	gpp_DistributionMadeToLimitedPartnerAndGeneralPartnerSecondQualifierPercentageDistributionArrearages
Namespace Prefix:	gpp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Distribution Made to Limited Partners and General Partner, Cash Distributions Declared

No definition available.

Name:	gpp_DistributionMadeToLimitedPartnersAndGeneralPartnerCashDistributionsDeclared
Namespace Prefix:	gpp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Incentive Distribution Rights, Maximum Ownership Percentage by General Partner

No definition available.

Name:	gpp_IncentiveDistributionRightsMaximumOwnershipPercentageByGeneralPartner
Namespace Prefix:	gpp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Per unit of ownership amount of cash distributions declared to unit-holder of a limited partnership (LP).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Name:	us-gaap_DistributionMadeToLimitedPartnerDistributionsDeclaredPerUnit
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

Per unit of ownership amount of cash distributions paid to unit-holder of a limited partnership (LP).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

Name:	us-gaap_DistributionMadeToLimitedPartnerDistributionsPaidPerUnit
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
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_LimitedPartnersCapitalAccountLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Percentage of subsidiary's or equity investee's stock owned by parent company after stock transaction.

No definition available.

Name:	us-gaap_SaleOfStockPercentageOfOwnershipAfterTransaction
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_PartnerTypeOfPartnersCapitalAccountAxis=us-gaap_GeneralPartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementClassOfStockAxis=gpp_SubordinatedUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis=gpp_ThreeConsecutiveFourQuarterPeriodsEndingOnOrAfterJune302018Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DistributionsMadeToMemberOrLimitedPartnerByDistributionTypeAxis=gpp_AnyFourQuarterPeriodEndingOnOrAfterJune302016ProvidedNoArrearagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: