Note 9 - Discontinued Operations (Details Textual)	1 Months Ended	12 Months Ended
Dec. 31, 2019 USD ($) a	Dec. 31, 2019 USD ($) a	Dec. 31, 2018 USD ($)
Kapalua Mauka [Member]
Area of Real Estate Property \| a	125	125
Discontinued Operations, Disposed of by Sale [Member] \| PUC-regulated Assets [Member] \| Kapalua Water Company and Kapalua Waste Treatment Company [Member] \| Kapalua Resort [Member]
Disposal Group, Including Discontinued Operation, Consideration	$ 3,800,000	$ 3,800,000
Asset Purchase Agreement, Deliver Water Agreement, Initial Term	20 years
Disposal Group Including Discontinued Operation, Excluded From Purchase Price	$ 3,600,000	3,600,000
Discontinued Operations [Member]
Payments to Acquire Property, Plant, and Equipment, Total		$ 626,000	$ 155,000

Represents the initial term of deliver water agreement for asset purchase agreement.

No definition available.

Name:	mlp_AssetPurchaseAgreementDeliverWaterAgreementInitialTerm
Namespace Prefix:	mlp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents amount of excluded form purchase price for disposal group including discontinued operation.

+ References

No definition available.

+ Details

Name:	mlp_DisposalGroupIncludingDiscontinuedOperationExcludedFromPurchasePrice
Namespace Prefix:	mlp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Area of a real estate property.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

+ References

No definition available.

+ Details

Name:	us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3213-108585

+ Details

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

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=mlp_KapaluaMaukaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DiscontinuedOperationsDisposedOfBySaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=mlp_PucregulatedAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=mlp_KapaluaWaterCompanyAndKapaluaWasteTreatmentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=mlp_KapaluaResortMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_SegmentDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: