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Basis of Preparation (Details) |  | 3 Months Ended |  | 3 Months Ended
--- | --- | --- | --- | ---
Mar. 22, 2013 | Mar. 31, 2013 Consolidated JV one item | Mar. 31, 2013 Consolidated JV one Minimum | Mar. 31, 2013 Consolidated JV one Maximum | Mar. 31, 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 |  |  |  |  | 6

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