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SUMMARY ACCOUNTING POLICIES (Details) | Jun. 30, 2021 USD ($) item
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Investment in Joint Ventures and Variable Interest Entities |
Number of Unconsolidated Joint Venture VIEs | item | 0
Recourse debt of joint ventures | $ | $ 0

X
- Definition Amount of debt for which the creditor has general recourse to the joint venture debtor. + References No definition available. + Details
Name: | olp_JointVentureRecourseDebt
Namespace Prefix: | olp_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Number of unconsolidated joint venture investments that are classified as a Variable Interest Entity (VIE). + References No definition available. + Details
Name: | olp_UnconsolidatedJointVentureVariableInterestEntityNumberOfEntities
Namespace Prefix: | olp_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_VariableInterestEntityNotPrimaryBeneficiaryDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration