RELATED PARTY TRANSACTIONS - Compensation and Services Agreement (Details) - USD ($)	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Affiliated Entity \| Majestic
Related Party Transactions
Aggregate fees under compensation and services agreement	$ 826,000	$ 879,000
Property management services	357,000	428,000
Additional payment for the entity's share of all direct office expenses	$ 84,000	$ 79,000
Affiliated Entity \| Majestic \| Net lease tenants
Related Party Transactions
Property management costs as a percentage of rental payments	1.50%	1.50%
Affiliated Entity \| Majestic \| Operating lease tenants
Related Party Transactions
Property management costs as a percentage of rental payments	2.00%	2.00%
Executive officers and others
Related Party Transactions
Stock incentive plan expense	$ 614,000	$ 642,000

Represents the amount of additional payment to related party for the share of direct office expenses.

No definition available.

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Balance Type:	debit
Period Type:	duration

- Definition

Represents the amount to be paid under the agreement with the related party.

+ References

No definition available.

+ Details

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- Definition

Represents the amount of property management costs allocated to real estate expenses.

+ References

No definition available.

+ Details

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

- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479830/718-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

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

- Definition

The percentage charged for managing real estate properties.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c)(2)(i))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c)(2)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

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- Details

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- Details

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- Details

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- Details

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