Related Party Transactions (Details) (USD $)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Majestic
Related Party Transaction
Quarterly fees under compensation and services agreement	$ 633,750	$ 825,000
Overhead expenses under compensation and services agreement	48,900	46,600
Management fees under compensation and services agreement	223,100	212,500
Chairman
Related Party Transaction
Quarterly fees under compensation and services agreement	65,625	62,500
Vice Chairman
Related Party Transaction
Quarterly fees under compensation and services agreement	26,250	25,000
Gould Investors L.P.
Related Party Transaction
Share of property insurance premiums	57,000	50,000
Joint venture partners
Related Party Transaction
Real estate management and acquisition costs	$ 105,000	$ 12,000

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

No definition available.

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- 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 management fees included in 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 overhead expenses included in 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

A contract to provide coverage or protection in exchange for a payment or "premium". Examples of insurance protection include liability and property insurance. The entity paying the premiums for the protection will have insurance expense and possibly an asset, Prepaid Insurance (if the premiums are paid in advance).

+ 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 210.5-03.6)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

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Period Type:	duration

- Details

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- Details

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- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=olp_GouldInvestorsLPMember
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- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=olp_MajesticPropertyManagementCorpMember
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- Details

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- Details

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