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

Amount of debt for which the creditor has general recourse to the joint venture debtor.

No definition available.

Name:	olp_JointVentureRecourseDebt
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Represent the percentage of the company's rental income accounted by the tenant.

No definition available.

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

Maximum useful life of finite-lived intangible assets and long lived, physical assets used in the normal conduct of business and not intended for resale.

No definition available.

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

Representing aggregate provision for doubtful accounts of rental income, tenant reimbursements and unbilled rent receivable.

No definition available.

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

Represents the amounts related to Real estate taxes, insurance and other escrows related to real estate in escrow, deposits and other assets and receivables.

No definition available.

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

Number of unconsolidated joint venture investments that are classified as a Variable Interest Entity (VIE).

No definition available.

Name:	olp_UnconsolidatedJointVentureVariableInterestEntityNumberOfEntities
Namespace Prefix:	olp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Represents information pertaining to write-off of straight line rent.

No definition available.

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

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

No definition available.

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

For an unclassified balance sheet, a valuation allowance for receivables due a company that are expected to be uncollectible.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5074-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.4)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e25351-111560

Name:	us-gaap_ImpairmentOfInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64862545&loc=d3e2921-110230

Reference 2: 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=66902209&loc=d3e3602-108585

Name:	us-gaap_ImpairmentOfRealEstate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of expense related to write-down of receivables to the amount expected to be collected. Includes, but is not limited to, accounts receivable and notes receivable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.5)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Name:	us-gaap_ProvisionForDoubtfulAccounts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

No definition available.

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

The book value of investments in real estate joint ventures including direct and indirect investments.

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(d))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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

No definition available.

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

No definition available.

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

In accordance with the provisions of their lease agreement, this element represents allowable charges due a landlord from its tenant. In retail store and office building leases, for example, tenant reimbursements may cover items such as taxes, utilities, and common area expenses.

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

No definition available.