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Basis of Preparation (Details)	9 Months Ended
	Sep. 30, 2013 item
Consolidated JV one
Investment in Joint Ventures
Number of controlling interest in joint ventures	5
Consolidated JV one | Minimum
Investment in Joint Ventures
Ownership interest in consolidated joint venture (as a percent)	85.00%
Consolidated JV one | Maximum
Investment in Joint Ventures
Ownership interest in consolidated joint venture (as a percent)	95.00%
Consolidated JV two
Investment in Joint Ventures
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