Percentage of average annual return on capital used as the performance criteria for an equity incentive plan.

No definition available.

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

- Definition

Percentage of average annual total stockholder return used as the performance criteria for an equity incentive plan.

+ References

No definition available.

+ Details

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

- Definition

The number of shares not earned during the period due to metrics not met on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

No definition available.

+ Details

Name:	olp_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsSharesNotEarnedDueToMetricsNotMet
Namespace Prefix:	olp_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the total fair value of other than stock (or unit) option plans granted during the reporting period.

+ References

No definition available.

+ Details

Name:	olp_ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherThanOptionsForfeituresInPeriodWeightedAverageIntrinsicValue
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of obligations, excluding pension and other postretirement benefits, incurred through that date and payable for perquisites provided to employees pertaining to services received from them.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15(a))
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15(5))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

+ Details

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

- Definition

Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- 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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of vesting of award under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=olp_AwardsGrantedIn2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=olp_ShareBasedPaymentArrangementVestingJune302025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=olp_AwardsGrantedIn2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=olp_ShareBasedPaymentArrangementVestingJune302024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=olp_AwardsGrantedIn2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=olp_ShareBasedPaymentArrangementVestingJune302023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=olp_AwardsGrantedIn2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=olp_ShareBasedPaymentArrangementVestingJune302022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=olp_AwardsGrantedIn2018Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=olp_ShareBasedPaymentArrangementVestingJune302021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=olp_RestrictedStockUnitsRsusAverageAnnualReturnOnCapitalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardDateAxis=olp_IncentivePlansForYears20182019And2020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_AwardDateAxis=olp_IncentivePlansForYears2021And2022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=olp_TotalStockholderReturnAwardsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=olp_PayForPerformanceProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

STOCKHOLDERS' EQUITY - Stock Based Compensation - RSUs (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2019	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021	Dec. 31, 2020
Restricted stock units
Stock Based Compensation
Number of shares vested	64,488	73,750	64,488	73,750
Number of shares forfeited	10,538		10,538
Number of shares outstanding	155,726	150,052	155,726	150,052		230,752	230,752	223,802	223,802
Number of shares not earned due to applicable market conditions not being satisfied			10,538
Performance cycle			3 years
Restricted stock units \| Awards granted in 2022 \| Vesting Date: June 30, 2025
Stock Based Compensation
Number of shares granted			85,350
Number of shares outstanding	85,350		85,350
Restricted stock units \| Awards granted in 2021
Stock Based Compensation
Aggregate fair value of the shares granted	$ 1,846,000		$ 1,846,000
Restricted stock units \| Awards granted in 2021 \| Vesting Date: June 30, 2024
Stock Based Compensation
Number of shares granted			80,700
Number of shares outstanding	80,700		80,700
Restricted stock units \| Awards granted in 2020
Stock Based Compensation
Aggregate fair value of the shares granted	$ 962,000		$ 962,000
Restricted stock units \| Awards granted in 2020 \| Vesting Date: June 30, 2023
Stock Based Compensation
Number of shares granted			75,026
Number of shares outstanding	75,026		75,026
Restricted stock units \| Awards granted in 2019
Stock Based Compensation
Number of shares forfeited					2,750
Restricted stock units \| Awards granted in 2019 \| Vesting Date: June 30, 2022
Stock Based Compensation
Number of shares granted			77,776
Number of shares vested			64,488
Number of shares forfeited			13,288
Restricted stock units \| Awards granted in 2018
Stock Based Compensation
Number of shares forfeited					2,500
Restricted stock units \| Awards granted in 2018 \| Vesting Date: June 30, 2021
Stock Based Compensation
Number of shares granted			76,250
Number of shares vested			73,750
Number of shares forfeited			2,500
ROC Awards \| Awards granted in 2021
Stock Based Compensation
Accrual for dividend equivalent rights	$ 108,000		$ 108,000
ROC Awards \| Years granted: 2018 - 2020
Stock Based Compensation
Weight			50.00%
ROC Awards \| Years granted: 2018 - 2020 \| Minimum
Stock Based Compensation
Average of annual ROC			7.00%
ROC Awards \| Years granted: 2018 - 2020 \| Maximum
Stock Based Compensation
Average of annual ROC			9.75%
ROC Awards \| Years granted: 2021 - 2022
Stock Based Compensation
Weight			50.00%
ROC Awards \| Years granted: 2021 - 2022 \| Minimum
Stock Based Compensation
Average of annual ROC			6.00%
ROC Awards \| Years granted: 2021 - 2022 \| Maximum
Stock Based Compensation
Average of annual ROC			8.75%
TSR awards
Stock Based Compensation
Performance cycle			3 years
TSR awards \| Years granted: 2018 - 2020
Stock Based Compensation
Weight			50.00%
TSR awards \| Years granted: 2018 - 2020 \| Minimum
Stock Based Compensation
Average of annual TSR			7.00%
TSR awards \| Years granted: 2018 - 2020 \| Maximum
Stock Based Compensation
Average of annual TSR			12.00%
TSR awards \| Years granted: 2021 - 2022
Stock Based Compensation
Weight			50.00%
TSR awards \| Years granted: 2021 - 2022 \| Minimum
Stock Based Compensation
Average of annual TSR			6.00%
TSR awards \| Years granted: 2021 - 2022 \| Maximum
Stock Based Compensation
Average of annual TSR			11.00%
Pay-for-performance program \| Restricted stock units
Stock Based Compensation
Vesting period			3 years
Number of shares vested	0		0
Number of shares forfeited	0		0