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SUMMARY ACCOUNTING POLICIES (Details)	Jun. 30, 2021 USD ($) item
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