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

No definition available.

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Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
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

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

- Definition

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

+ References

No definition available.

+ Details

Name:	olp_RelatedPartyTransactionPropertyManagementCostAllocatedToRealEstateExpenses
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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
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

Name:	us-gaap_PropertyManagementFeePercentFee
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

No definition available.

+ Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=olp_MajesticPropertyManagementCorpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MajorCustomersAxis=olp_NetLeasePropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MajorCustomersAxis=olp_OperatingLeasePropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=olp_ExecutiveOfficersAndOthersMember
Namespace Prefix:
Data Type:	na
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RELATED PARTY TRANSACTIONS - Compensation and Services Agreement (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Majestic
Related Party Transactions
Aggregate fees under compensation and services agreement	$ 760,000	$ 780,000	$ 1,526,000	$ 1,564,000
Property management services	329,000	343,000	666,000	691,000
Additional payment for the entity's share of all direct office expenses	79,000	74,000	$ 159,000	148,000
Majestic \| Net lease tenants
Related Party Transactions
Property management costs as a percentage of rental payments			1.50%
Majestic \| Operating lease tenants
Related Party Transactions
Property management costs as a percentage of rental payments			2.00%
Executive officers and others
Related Party Transactions
Stock incentive plan expense	$ 643,000	$ 739,000	$ 1,287,000	$ 1,390,000