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RELATED PARTY TRANSACTIONS - Joint Venture Partners and Affiliates (Details) - USD ($) | 3 Months Ended
--- | ---
Mar. 31, 2022 | Mar. 31, 2021
Unconsolidated Joint Ventures |  |
Related Party Transactions |  |
Payments for property management services | $ 36,000 | $ 29,000
Decrease in equity earnings, joint venture transaction | 18,000 | 15,000
Joint Venture Partners and Affiliates |  |
Related Party Transactions |  |
Payments for property management services | $ 22,000 | $ 19,000

X
- Definition Reduction of equity in earnings of unconsolidated joint ventures on the consolidated statement of income. + References No definition available. + Details
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Namespace Prefix: | olp_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the aggregate costs related to management of properties during the reporting period. + References No definition available. + Details
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Namespace Prefix: | olp_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |