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 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

Amount of other assets and receivables written off due to sale of related real estate property.

+ References

No definition available.

+ Details

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

- 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

The charge against earnings in the period to reduce the carrying amount of real property to fair value.

+ 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 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482099/360-10-50-2

+ Details

Name:	us-gaap_ImpairmentOfRealEstate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_HobbyLobbyRetailPropertyInWoodburyMinnesotaMember
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_ConsolidatedEntitiesAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=olp_VariableInterestEntityOnePrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=olp_VariableInterestEntityTwoPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

SALES OF PROPERTIES AND IMPAIRMENT LOSS (Details) - USD ($)														3 Months Ended		9 Months Ended
	Sep. 16, 2024	Aug. 29, 2024	Aug. 15, 2024	Jun. 28, 2024	Jun. 10, 2024	Jun. 07, 2024	Jun. 06, 2024	May 09, 2024	May 06, 2024	Mar. 06, 2024	Sep. 20, 2023	May 31, 2023	Feb. 28, 2023	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
SALES OF PROPERTIES
Gain on sale of real estate, net														$ 2,115,000	$ 332,000	$ 11,347,000	$ 5,046,000
Impairment loss																1,086,000
Properties disposed of by sale
SALES OF PROPERTIES
Gross Sales Price																39,445,000	13,450,000
Gain on sale of real estate, net																11,347,000	5,046,000
Mortgage prepaid on sale of real estate																10,714,000
Reduction to Gain on sale of real estate, net, attributable to the write-off of unbilled rent receivable																285,000	123,000
Reduction to Gain on sale of real estate, net, attributable to the write-off of net unamortized lease liabilities and assets																64,000
Reduction to Gain on sale of real estate, net, attributable to the write-off of other assets and receivables																108,000	$ 190,000
Properties disposed of by sale \| Hacienda Colorado restaurant parcel in Lakewood, Colorado
SALES OF PROPERTIES
Gross Sales Price										$ 2,900,000
Gain on sale of real estate, net										1,784,000
Properties disposed of by sale \| Applebee's restaurant property in Kennesaw, Georgia
SALES OF PROPERTIES
Gross Sales Price									$ 2,834,000
Gain on sale of real estate, net									$ 964,000
Properties disposed of by sale \| FedEx industrial property in Miamisburg, Ohio
SALES OF PROPERTIES
Gross Sales Price								$ 2,793,000
Gain on sale of real estate, net								$ 1,507,000
Properties disposed of by sale \| Havertys retail property in Wichita, Kansas
SALES OF PROPERTIES
Gross Sales Price							$ 6,600,000
Gain on sale of real estate, net							$ 1,884,000
Properties disposed of by sale \| Urban Outfitters retail property in Lawrence, Kansas
SALES OF PROPERTIES
Gross Sales Price						$ 1,300,000
Gain on sale of real estate, net						$ 43,000
Properties disposed of by sale \| Walgreens retail property in Cape Girardeau, Missouri
SALES OF PROPERTIES
Gross Sales Price					$ 2,793,000
Gain on sale of real estate, net					978,000
Properties disposed of by sale \| Vacant retail property in Kennesaw, Georgia
SALES OF PROPERTIES
Gross Sales Price				$ 6,700,000
Gain on sale of real estate, net				$ 2,072,000
Properties disposed of by sale \| Vacant health and fitness property in Hamilton, Ohio
SALES OF PROPERTIES
Gross Sales Price			$ 4,350,000
Gain on sale of real estate, net			$ 17,000
Impairment loss																$ 1,086,000
Properties disposed of by sale \| Vacant industrial property in Wauconda, IL
SALES OF PROPERTIES
Gross Sales Price		$ 4,425,000
Gain on sale of real estate, net		$ 1,177,000
Properties disposed of by sale \| Hobby Lobby retail property in Woodbury, Minnesota
SALES OF PROPERTIES
Gross Sales Price	$ 4,750,000
Gain on sale of real estate, net	$ 921,000
Properties disposed of by sale \| TGI Fridays restaurant property in Hauppauge, New York
SALES OF PROPERTIES
Gross Sales Price													$ 4,200,000
Gain on sale of real estate, net													$ 1,534,000
Properties disposed of by sale \| Havertys retail property in Duluth, Georgia
SALES OF PROPERTIES
Gross Sales Price												$ 6,000,000
Gain on sale of real estate, net												$ 3,180,000
Properties disposed of by sale \| TGI Fridays restaurant property in Greensboro, North Carolina
SALES OF PROPERTIES
Gross Sales Price											$ 3,250,000
Gain on sale of real estate, net											$ 332,000
Consolidated Joint Venture-VIEs \| Properties disposed of by sale \| Hacienda Colorado restaurant parcel in Lakewood, Colorado
SALES OF PROPERTIES
Mortgage prepaid on sale of real estate										1,885,000
Non-controlling interest's share of the gain										$ 178,000
Consolidated Joint Venture-VIEs \| Properties disposed of by sale \| Walgreens retail property in Cape Girardeau, Missouri
SALES OF PROPERTIES
Non-controlling interest's share of the gain					$ 105,000
Consolidated VIE 1
SALES OF PROPERTIES
Ownership interest in consolidated joint venture of the company (as a percent)																90.00%
Consolidated VIE 1 \| Properties disposed of by sale \| Hacienda Colorado restaurant parcel in Lakewood, Colorado
SALES OF PROPERTIES
Ownership interest in consolidated joint venture of the company (as a percent)										90.00%
Consolidated VIE 2
SALES OF PROPERTIES
Ownership interest in consolidated joint venture of the company (as a percent)																95.00%
Consolidated VIE 2 \| Properties disposed of by sale \| Walgreens retail property in Cape Girardeau, Missouri
SALES OF PROPERTIES
Ownership interest in consolidated joint venture of the company (as a percent)					95.00%