Represents the amount of difference between the carrying value and the fair value.

No definition available.

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Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
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- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations before netting of deferred finance costs. Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

No definition available.

+ Details

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

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- Definition

The charge against earnings in the period to reduce the carrying amount of real property to fair value.

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Balance Type:	debit
Period Type:	duration

- Definition

Fair value portion of contractual arrangement with a lender under which borrowings can be made up to a specific amount at any point in time.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Value of input used to measure long-term debt.

+ References

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Weighted average interest rate of long-term debt outstanding calculated over time.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
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- Details

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- Details

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FAIR VALUE MEASUREMENTS (Details)	3 Months Ended		9 Months Ended		12 Months Ended
FAIR VALUE MEASUREMENTS (Details)	Sep. 30, 2026 USD ($) Y	Sep. 30, 2025 USD ($)	Sep. 30, 2026 USD ($) Y	Sep. 30, 2025 USD ($)	Dec. 31, 2025 USD ($) Y
FAIR VALUE MEASUREMENTS
Line of credit, fair value	$ 10,000,000		$ 10,000,000
Impairment loss	1,422,000	$ 1,300,000	1,564,000	$ 1,300,000
Properties held-for-sale \| TVI, Inc. retail property, Chicago, Illinois
FAIR VALUE MEASUREMENTS
Impairment loss	1,422,000		1,564,000
Properties held-for-sale \| Property in Beachwood, Ohio
FAIR VALUE MEASUREMENTS
Impairment loss		$ 1,300,000		$ 1,300,000
Mortgages payable
FAIR VALUE MEASUREMENTS
Fair value of mortgages payable	513,088,000		513,088,000		$ 517,660,000
Carrying value of mortgages payable, gross	538,375,000		538,375,000		522,501,000
Fair value less than carrying value	$ (25,287,000)		$ (25,287,000)		$ (4,841,000)
Weighted average interest rate			4.98%		4.88%
Mortgages payable \| Blended market interest rate
FAIR VALUE MEASUREMENTS
Long-term debt, measurement input	0.0651		0.0651		0.0544
Mortgages payable \| Weighted average remaining term to maturity (years)
FAIR VALUE MEASUREMENTS
Long-term debt, measurement input \| Y	5.3		5.3		5.8