Aggregate fees paid to other partners of the venture.

No definition available.

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

- Definition

Reduction of equity in earnings of unconsolidated joint ventures on the consolidated statement of income.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Insurance expense recognized of amounts reimbursed to related party

+ References

No definition available.

+ Details

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

- Definition

Represents the aggregate costs related to management of properties during the reporting period.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of additional payment to related party for the share of direct office expenses.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of reimbursement of property insurance under the related party transactions.

+ References

No definition available.

+ Details

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Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Represents the amount to be paid under the agreement with the related party.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of property management costs allocated to real estate expenses.

+ References

No definition available.

+ Details

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

- Definition

Represents the quarterly amount to be paid under the agreement with the related party for the current fiscal year.

+ References

No definition available.

+ Details

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

- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The percentage charged for managing real estate properties.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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

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

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- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_CoVenturerMember
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- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_CorporateJointVentureMember
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Data Type:	na
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Period Type:

- Details

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- Details

Name:	us-gaap_MajorPropertyClassAxis=olp_NetLeasePropertyMember
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Related Party Transactions (Details) - USD ($)	3 Months Ended		9 Months Ended
Related Party Transactions (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Related Party Transaction
Share based compensation charged to operations	$ 971,000	$ 684,000	$ 2,653,000	$ 2,341,000
Majestic
Related Party Transaction
Fees under compensation and services agreement	687,000	667,000	2,054,000	1,996,000
Property management costs allocated to real estate expenses	307,000	287,000	915,000	857,000
Additional payment for the entity's share of all direct office expenses	54,000	54,000	162,000	162,000
Executive officers and others
Related Party Transaction
Share based compensation charged to operations	483,000	361,000	1,332,000	1,128,000
Joint venture partners
Related Party Transaction
Real estate property management costs	21,000	30,000	86,000	112,000
Corporate joint venture
Related Party Transaction
Aggregate fees paid to other partners	39,000	45,000	135,000	132,000
Decrease in equity earnings, joint venture transaction	19,000	22,000	67,000	66,000
Chairman \| General and administrative expense
Related Party Transaction
Quarterly fees under compensation and services agreement	69,000	69,000
Vice Chairman \| General and administrative expense
Related Party Transaction
Quarterly fees under compensation and services agreement	27,500	27,500
Gould Investors L.P.
Related Party Transaction
Amount of insurance reimbursed	912,000	782,000	912,000	782,000
Insurance expense recognized of amounts reimbursed to related party	$ 241,000	$ 204,000	$ 646,000	$ 551,000
Net lease tenants \| Majestic
Related Party Transaction
Property management fee (as a percent)			1.50%
Operating lease tenants \| Majestic
Related Party Transaction
Property management fee (as a percent)			2.00%