RELATED PARTY TRANSACTIONS - Other (Details) - USD ($)	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Real estate expenses
Related Party Transactions
Insurance expense recognized of amounts reimbursed to related party	$ 944,000	$ 1,267,000	$ 1,091,000
Chairman \| General and administrative expense
Related Party Transactions
Aggregate fees paid	313,000	298,000	298,000
Vice Chairman \| General and administrative expense
Related Party Transactions
Aggregate fees paid	125,000	119,000	119,000
Gould Investors L.P.
Related Party Transactions
Amount of insurance reimbursed	$ 586,000	$ 1,402,000	$ 1,168,000
Number of common stock shares owned by the related party	1,998,535	1,921,712
Ownership percentage held by a related party	9.50%	9.20%

Number of shares of common stock owned by related party

No definition available.

Name:	olp_AmountOfSharesOfCommonStockOwnedByRelatedParty
Namespace Prefix:	olp_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Insurance expense recognized of amounts reimbursed to related party

+ References

No definition available.

+ Details

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

- Definition

The aggregate amount of payments for key management services.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of reimbursement of property insurance under the related party transactions.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of ownership held by the related party.

+ References

No definition available.

+ Details

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

- 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_IncomeStatementLocationAxis=olp_RealEstateExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_GeneralAndAdministrativeExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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