Represents number of proberties hold by tenant.

No definition available.

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Represents information pertaining to write-off of tenant origination costs.

+ References

No definition available.

+ Details

Name:	olp_WriteOffOfTenantOriginationCosts
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

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

- Definition

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

+ References

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

+ Details

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

- Definition

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

+ References

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

+ Details

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

- Definition

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.

+ References

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

+ Details

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

- Definition

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

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

+ Details

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

- Details

Name:	us-gaap_CounterpartyNameAxis=olp_HhgreggInc.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CounterpartyNameAxis=olp_SportsAuthorityInc.Member
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:

Allowance for Doubtful Accounts (Details)	1 Months Ended	3 Months Ended
Allowance for Doubtful Accounts (Details)	Mar. 31, 2017 USD ($) property	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Allowance for Doubtful Accounts
Balance in allowance for doubtful accounts	$ 0	$ 0		$ 0
Bad debt expense		296,000	$ 153,000
Hhgregg, Inc.
Allowance for Doubtful Accounts
Number of properties by tenant \| property	2
Bad debt expense		296,000
Write off of Unbilled Rent Receivable		263,000
Write off of tenant origination costs		646,000
Impairment charge		0
Net book value of property	$ 5,934,000	5,934,000
Sports Authority Inc.
Allowance for Doubtful Accounts
Bad debt expense			$ 153,000
Impairment charge		0
Net book value of property	$ 2,605,000	$ 2,605,000
Maximum \| Hhgregg, Inc.
Allowance for Doubtful Accounts
Percentage of rental income		1.50%	1.50%
Maximum \| Sports Authority Inc.
Allowance for Doubtful Accounts
Percentage of rental income			1.00%