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Basis of Preparation (Details)		6 Months Ended			6 Months Ended
	Mar. 22, 2013	Jun. 30, 2013 Consolidated JV one item	Jun. 30, 2013 Consolidated JV one Minimum	Jun. 30, 2013 Consolidated JV one Maximum	Jun. 30, 2013 Consolidated JV two item
Investment in Joint Ventures
Number of controlling interest in joint ventures		5
Ownership interest in consolidated joint venture (as a percent)	90.00%		85.00%	95.00%
Number of other unconsolidated joint ventures					5

X

- Definition

Represents the number of joint ventures in which entity has controlling interest.

+ References

No definition available.

+ Details

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

X

- Definition

Represents the number of unconsolidated joint ventures of the entity that are accounted for under the equity method of accounting.

+ References

No definition available.

+ Details

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

X

- Details

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

X

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant