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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