Name:	olp_PaymentsToAcquireRealEstateExcludingAcquisitionCosts
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
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Represents the real estate acquisition cost capitalized.

No definition available.

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Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

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_AssetAcquisitionLineItems
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Data Type:	xbrli:stringItemType
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Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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Balance Type:	na
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Amount of increase in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate, from new investment.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Footnote 6))
-URI http://asc.fasb.org/extlink&oid=120402547&loc=d3e617274-123014

Name:	us-gaap_MortgageLoansOnRealEstateNewMortgageLoans
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Data Type:	xbrli:monetaryItemType
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Name:	us-gaap_AssetAcquisitionAxis=olp_RealEstateAcquisitionsIn2021Member
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Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_PureonInc.IndustrialFacilityMonroeNorthCarolinaMember
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Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_MultiTenantIndustrialFacilityLehighAcresFloridaMember
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Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_HomeDepotUsaIncIndustrialFacilityOmahaNebraskaMember
Namespace Prefix:
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Name:	us-gaap_AssetAcquisitionAxis=olp_RealEstateAcquisitionsIn2020Member
Namespace Prefix:
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Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_CreativeOfficeEnvironmentsIndustrialFacilityAshlandVirginiaMember
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