Represents the percentage of company's total rental income generated by tenant during the reporting period.

No definition available.

Name:	olp_PercentageOfTotalRentalIncomeGeneratedByTenant
Namespace Prefix:	olp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the amount of unbilled rent receivable written off during the period.

+ References

No definition available.

+ Details

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

- Definition

Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

+ References

No definition available.

+ Details

Name:	us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The difference between the carrying value and the sale price of real estate or properties that were intended to be sold or held for capital appreciation or rental income. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

+ Details

Name:	us-gaap_GainLossOnSaleOfProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of investments in land and buildings held for sale, excluding real estate considered to be inventory of the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(f))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_RealEstateHeldforsale
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=olp_RealEstatePropertyLocatedInKilleenTexasMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=olp_RealEstateInvestmentsNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
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Period Type:

- Details

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Namespace Prefix:
Data Type:	na
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Subsequent Events (Details) - USD ($)	1 Months Ended	3 Months Ended
Subsequent Events (Details) - USD ($)	Mar. 31, 2015	Jun. 30, 2016	Mar. 31, 2016	Mar. 31, 2015	Apr. 20, 2016	Dec. 31, 2015
Subsequent Events
Net book value of properties held for sale						$ 12,259,000
Write-off of unbilled rent receivable	$ 226,000			$ 226,000
Property located in Killeen, Texas \| Contract to sell property \| Maximum
Subsequent Events
Percentage of company's rental income generated by tenant			0.40%	0.40%
Property located in Killeen, Texas \| Contract to sell property \| Real estate investments, net
Subsequent Events
Net book value of properties held for sale			$ 1,975,000			$ 1,983,000
Subsequent Event \| Property located in Killeen, Texas \| Contract to sell property
Subsequent Events
Contract to sell property, consideration, net of closing costs					$ 3,000,000
Subsequent Event \| Forecast \| Property located in Killeen, Texas \| Contract to sell property
Subsequent Events
Gain on sale of property		$ 1,000,000
Write-off of unbilled rent receivable		$ 33,000