INCOME TAXES (Details) - USD ($)	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Nov. 30, 2024
INCOME TAXES
Period of disqualification of REIT status	4 years
Approximate allocation of the distributions made to stockholders (percentages):
Ordinary income	55.00%	53.00%	54.00%
Capital gains	45.00%	47.00%	46.00%
Total distributions made to stockholders	100.00%	100.00%	100.00%
Reconciliation between dividends declared with the dividends paid deduction
Dividends declared	$ 38,421,000	$ 38,116,000	$ 37,915,000
Dividend reinvestment plan	71,000	157,000	102,000
Dividends before adjustments	38,492,000	38,273,000	38,017,000
Less: Spillover dividends designated to previous year	(740,000)	(4,240,000)
Less: Spillover dividends designated to following year	(5,952,000)
Plus: Dividends designated from prior year			2,085,000
Plus: Dividends designated from following year		740,000	4,240,000
Dividends paid deduction	$ 31,800,000	$ 34,773,000	$ 44,342,000
Percentage of discount on common stock purchased through the dividend reinvestment plan	3.00%	3.00%	3.00%
Maximum
Reconciliation between dividends declared with the dividends paid deduction
Percentage of discount on common stock purchased through the dividend reinvestment plan	5.00%
Tennessee
INCOME TAXES
Refund related to franchise taxes paid 2020 - 2022				$ 238,000

No definition available.

Name:	olp_DisclosureOfAllocationOfDistributionsMadeToStockholdersAbstract
Namespace Prefix:	olp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of distributions made to stockholders

+ References

No definition available.

+ Details

Name:	olp_DistributionsMadeToStockholdersPercentage
Namespace Prefix:	olp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the amount of dividends paid to stockholders that are deducted from the entity's taxable income.

+ References

No definition available.

+ Details

Name:	olp_DividendPaidDeductionFromTaxableIncome
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the amount of discount on common stock purchased through the dividend reinvestment plan.

+ References

No definition available.

+ Details

Name:	olp_DividendReinvestmentPlanCommonStockDiscountOnShares
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the amount of dividends before adjustments for dividends designated to previous year and designated from following year.

+ References

No definition available.

+ Details

Name:	olp_DividendsBeforeAdjustmentsForPreviousAndCurrentYear
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Dividends declared for reconciliation to dividends paid deduction.

+ References

No definition available.

+ Details

Name:	olp_DividendsDeclaredReconciliation
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the amount of dividends designated from the following year.

+ References

No definition available.

+ Details

Name:	olp_DividendsDesignatedFromFollowingYear
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the amount of dividends designated from the prior year.

+ References

No definition available.

+ Details

Name:	olp_DividendsDesignatedFromPriorYear
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the amount of dividends designated to the following year.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of dividends designated to the previous year.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

Name:	olp_IncomeTaxLineItems
Namespace Prefix:	olp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of discount from market price on common stock purchased through the dividend reinvestment plan.

+ References

No definition available.

+ Details

Name:	olp_PercentageOfDiscountOnCommonStockPurchasedThroughDividendReinvestmentPlan
Namespace Prefix:	olp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of distributions which represent capital gains to shareholders.

+ References

No definition available.

+ Details

Name:	olp_PercentageOfDistributionsRepresentingCapitalGainsToShareholders
Namespace Prefix:	olp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of distributions which represent ordinary income to shareholders.

+ References

No definition available.

+ Details

Name:	olp_PercentageOfDistributionsRepresentingOrdinaryIncomeToShareholders
Namespace Prefix:	olp_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	olp_ReconciliationOfCashDividendsPaidToDividendsPaidDeductionAbstract
Namespace Prefix:	olp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the subsequent period during which the entity would be disqualified as a real estate investment trust, if during any tax year the entity fails to qualify as a real estate investment trust.

+ References

No definition available.

+ Details

Name:	olp_SubsequentDisqualificationPeriodIfFailedToQualifyAsREIT
Namespace Prefix:	olp_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the additional liability or refund received or expected based on a final settlement with a taxing authority.

+ References

No definition available.

+ Details

Name:	us-gaap_IncomeTaxExaminationLiabilityRefundAdjustmentFromSettlementWithTaxingAuthority
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeTaxAuthorityNameAxis=olp_TennesseeDepartmentOfRevenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: