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

Incentive Distribution, Percentage Of Available Cash Distributed From Operating Surplus

No definition available.

Name:	gpp_IncentiveDistributionPercentageOfAvailableCashDistributedFromOperatingSurplus
Namespace Prefix:	gpp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

Amount of equity impact of cash distribution declared to unit-holder of limited partnership (LP).

Name:	us-gaap_DistributionMadeToLimitedPartnerCashDistributionsDeclared
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of cash distribution paid to unit-holder of limited partnership (LP).

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

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

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

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

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

Per-share or per-unit amount of incentive dividend declared and paid to managing member or general partner.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI https://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 73
-URI https://asc.fasb.org/extlink&oid=6926462&loc=SL5163674-159010

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 72
-URI https://asc.fasb.org/extlink&oid=6926462&loc=SL5163672-159010

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 55
-Paragraph 103
-URI https://asc.fasb.org/extlink&oid=109243028&loc=SL5199526-159011

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types: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.