Amount of difference between the carrying amount and the sales price of real estate properties sold.

No definition available.

Name:	olp_GainLossOnDispositionOfRealEstate
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Gross proceeds received from the sale of real estate during the current period.

+ References

No definition available.

+ Details

Name:	olp_GrossProceedsFromSaleOfRealEstate
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The term which a loan receivable may be extended at the borrower's option, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	olp_LoanReceivableOptionToExtendTerm
Namespace Prefix:	olp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of interest on loan receivable.

+ References

No definition available.

+ Details

Name:	olp_LoansReceivableFixedRate
Namespace Prefix:	olp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow to repay long-term debt that is wholly or partially secured by collateral upon sale of the property.

+ References

No definition available.

+ Details

Name:	olp_MortgagesPrepaidOnSaleOfProperty
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Income (loss) from sale of consolidated JV property attributable to noncontrolling interest.

+ References

No definition available.

+ Details

Name:	olp_NoncontrollingInterestShareOfGain
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of reduction to gain on sale of properties attributable to write-off of other assets and receivables.

+ References

No definition available.

+ Details

Name:	olp_ReductionToNetGainOnSaleOfPropertiesAttributableToWriteOffOfOtherAssetsAndReceivables
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of contracted sale price for property held-for-sale.

+ References

No definition available.

+ Details

Name:	olp_SaleOfPropertyContractSalePrice
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the amount of unbilled rent receivable written off during the period relating to properties sold.

+ References

No definition available.

+ Details

Name:	olp_StraightLineRentReceivableWrittenOffRelatingToPropertySold
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount of write-off of net unamortized intangible lease liabilities and assets.

+ References

No definition available.

+ Details

Name:	olp_WriteOffNetUnamortizedIntangibleLeaseLiabilitiesAndAssets
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount write-off of the unamortized intangible lease assets.

+ References

No definition available.

+ Details

Name:	olp_WriteOffUnamortizedIntangibleLeaseAsset
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amortized cost, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479319/326-20-50-5

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481990/310-10-45-2

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

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

- Definition

The difference between the carrying value and the sale price of real estate or properties that were intended to be sold or held for capital appreciation or rental income. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482130/360-10-45-5

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482099/360-10-50-3

+ Details

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

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481303/470-50-40-2

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481303/470-50-40-4

+ Details

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

- Definition

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.

+ References

No definition available.

+ Details

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

- Definition

Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481203/810-10-50-5A

+ Details

Name:	us-gaap_VariableInterestEntityOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_ApplebeesRestaurantInLawrencevilleGeorgiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_TgiFridaySRestaurantHauppaugeNewYorkMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_HavertysRetailPropertyDuluthGeorgiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_TgiFridaysRestaurantGreensboroNorthCarolinaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_LandLocatedInLakewoodColoradoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_ChuckECheeseRestaurantPropertyInIndianapolisIndianaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_TgiFridaysRestaurantPropertyRichmondVirginiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_TwoApplebeesRestaurantsInGeorgiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_HavertysRetailPropertyInVirginiaBeachVirginiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_BarnesAndNobleRetailPropertyInFortMyersFloridaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_WendySRestaurantsFourPropertiesVariousCitiesPennsylvaniaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_OrlandoBakingIndustrialPropertyColumbusOhioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_HavertysRetailPropertyFayettevilleGeorgiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_VacantRetailPropertyColumbusOhioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_WholeFoodsRetailPropertyAndParkingLotWestHartfordConnecticutMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_VacantRetailPropertyPhiladelphiaPennsylvaniaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_WendysRestaurantsTwoPropertiesInHanoverAndGettysburgPennsylvaniaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_PadSiteAtMultiTenantShoppingCenterInLakewoodColoradoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

SALES OF PROPERTIES (Details) - USD ($)																			3 Months Ended	12 Months Ended
SALES OF PROPERTIES (Details) - USD ($)	Jan. 19, 2024	Dec. 21, 2023	Dec. 15, 2023	Dec. 07, 2023	Dec. 05, 2023	Nov. 17, 2023	Nov. 15, 2023	Nov. 14, 2023	Sep. 20, 2023	May 31, 2023	Feb. 28, 2023	Aug. 08, 2022	Jun. 17, 2022	May 02, 2022	Mar. 22, 2022	Dec. 27, 2021	Jul. 01, 2021	Jun. 17, 2021	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Prepayment costs on debt																						$ 901,000
Reduction to Gain on sale of real estate, net, attributable to the write-off of unbilled rent receivable.																				$ 1,048,000	$ 519,000	1,438,000
Gain on sale of real estate, net																				17,008,000	16,762,000	25,463,000
Applebees restaurant property, Lawrenceville, Georgia
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Seller-financing provided by the Company				$ 1,816,000																1,816,000
Loan receivable interest rate				8.00%
Loan receivable, option to extend, term				6 months
Properties disposed of by sale
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price																				45,186,000	31,600,000	54,510,000
Gain on Sale of Real Estate, Net																				17,008,000	16,762,000	25,463,000
Mortgage Prepaid on Sale																						20,387,000
Prepayment costs on debt																						848,000
Reduction to Gain on sale of real estate, net, attributable to the write-off of unbilled rent receivable.																				1,005,000	519,000	1,438,000
Reduction to Gain on sale of real estate, net, attributable to the write-off of net unamortized lease liabilities and assets																				982,000	$ 4,000
Reduction to Gain on sale of real estate, net, attributable to the write-off of net unamortized lease assets																						$ 967,000
Reduction to Gain on sale of real estate, net, attributable to the write-off of other assets and receivables.																				$ 223,000
Properties disposed of by sale \| TGI Fridays Restaurant, Hauppauge, New York
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price											$ 4,200,000
Gain on Sale of Real Estate, Net											$ 1,534,000
Properties disposed of by sale \| Haverty's retail property, Duluth, Georgia
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price										$ 6,000,000
Gain on Sale of Real Estate, Net										$ 3,180,000
Properties disposed of by sale \| TGI Fridays Restaurant, Greensboro, North Carolina
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price									$ 3,250,000
Gain on Sale of Real Estate, Net									$ 332,000
Properties disposed of by sale \| Land, Lakewood, Colorado
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price								$ 3,333,000
Gain on Sale of Real Estate, Net								$ 2,177,000
Properties disposed of by sale \| Chuck E Cheese restaurant property, Indianapolis, Indiana
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price							$ 2,200,000
Gain on Sale of Real Estate, Net							$ 226,000
Properties disposed of by sale \| TGI Fridays restaurant property, Richmond, Virginia
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price						$ 3,200,000
Gain on Sale of Real Estate, Net						$ 265,000
Properties disposed of by sale \| Applebees restaurants - 2 properties, Cartersville & Carrolton, Georgia
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price					$ 7,300,000
Gain on Sale of Real Estate, Net					$ 2,581,000
Properties disposed of by sale \| Applebees restaurant property, Lawrenceville, Georgia
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price				$ 2,903,000
Gain on Sale of Real Estate, Net				$ 989,000
Properties disposed of by sale \| Havertys retail property, Virginia Beach, Virginia
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price			$ 5,500,000
Gain on Sale of Real Estate, Net			$ 1,727,000
Properties disposed of by sale \| Barnes & Noble retail property, Fort Myers, Florida
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price		$ 7,300,000
Gain on Sale of Real Estate, Net		$ 3,997,000
Properties disposed of by sale \| Wendy's restaurants - 4 properties, Various Cities, Pennsylvania
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price															$ 10,000,000
Gain on Sale of Real Estate, Net															$ 4,649,000
Properties disposed of by sale \| Orlando Baking industrial property, Columbus, Ohio
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price														$ 8,500,000
Gain on Sale of Real Estate, Net														$ 6,925,000
Properties disposed of by sale \| Haverty's retail property, Fayetteville, Georgia
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price													$ 4,800,000
Gain on Sale of Real Estate, Net													1,125,000
Mortgage Prepaid on Sale													$ 1,563,000
Properties disposed of by sale \| Vacant retail property, Columbus, Ohio
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price												$ 8,300,000
Gain on Sale of Real Estate, Net												$ 4,063,000
Properties disposed of by sale \| Whole Foods retail property & parking lot, West Hartford, Connecticut
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price																		$ 40,510,000
Gain on Sale of Real Estate, Net																		$ 21,469,000
Properties disposed of by sale \| Vacant retail property, Philadelphia, Pennsylvania
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price																	$ 8,300,000
Gain on Sale of Real Estate, Net																	$ 1,299,000
Ownership interest in consolidated joint venture of the company (as a percent)																	90.00%
Non-controlling interest's share of the gain																	$ 130,000
Properties disposed of by sale \| Wendy's restaurants - 2 properties, Hanover & Gettysburg, Pennsylvania
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Gross Sales Price																$ 5,700,000
Gain on Sale of Real Estate, Net																$ 2,695,000
Properties held-for-sale \| Pad site at a multi-tenant shopping center in Lakewood, Colorado
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Contracted sale price of property	$ 2,900,000
Consolidated Joint Venture-VIEs \| Properties disposed of by sale \| Land, Lakewood, Colorado
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Ownership interest in consolidated joint venture of the company (as a percent)								90.00%
Non-controlling interest's share of the gain								$ 218,000
Mortgage Prepaid on Sale								$ 1,116,000
Consolidated Joint Venture-VIEs \| Properties held-for-sale \| Pad site at a multi-tenant shopping center in Lakewood, Colorado
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Ownership interest in consolidated joint venture of the company (as a percent)	90.00%
Consolidated Joint Venture-VIEs \| Properties held-for-sale \| Pad site at a multi-tenant shopping center in Lakewood, Colorado \| Forecast
SALES OF PROPERTIES & PROPERTIE HELD-FOR-SALE
Non-controlling interest's share of the gain																			$ 180,000
Gain on sale of real estate, net																			$ 1,800,000