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Schedule III - Consolidated Real Estate and Accumulated Depreciation (Details) (USD $)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2014
Dec. 31, 2012
Dec. 31, 2011
Gross Amount at Which Carried        
Total $ 574,424,000us-gaap_RealEstateGrossAtCarryingValue 592,668,000us-gaap_RealEstateGrossAtCarryingValue $ 473,341,000us-gaap_RealEstateGrossAtCarryingValue $ 430,337,000us-gaap_RealEstateGrossAtCarryingValue
Accumulated Depreciation 73,060,000us-gaap_RealEstateAccumulatedDepreciation 77,643,000us-gaap_RealEstateAccumulatedDepreciation 62,816,000us-gaap_RealEstateAccumulatedDepreciation 54,214,000us-gaap_RealEstateAccumulatedDepreciation
Other disclosure        
Number of properties held-for-sale   2olp_NumberOfPropertiesHeldForSale    
Impairment loss/charge 62,000us-gaap_ImpairmentOfLongLivedAssetsToBeDisposedOf      
Minimum        
Other disclosure        
Estimated useful lives of buildings and improvements   3 years    
Maximum        
Other disclosure        
Estimated useful lives of buildings and improvements   40 years    
Industrial        
Other disclosure        
Reduction to cost of land and buildings   416,000olp_ReductionToLandAndBuildingsDueToReceiptOfRentalReserveFromSeller
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
   
Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   292,049,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Initial Cost To Company        
Land   168,737,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Buildings and Improvements   406,492,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   17,439,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Gross Amount at Which Carried        
Land   168,737,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Buildings and Improvements   423,931,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Total   59,668,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Accumulated Depreciation   77,643,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Other disclosure        
Number of properties net leased to same tenant pursuant to separate leases   8olp_RealEstateAndAccumulatedDepreciationNumberOfPropertiesNetLeasedToSameTenantUnderSeparateLeases
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Number of properties containing cross default provisions   5olp_RealEstateAndAccumulatedDepreciationNumberOfPropertiesContainingCrossDefaultProvisions
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Number of states in which properties containing cross default provisions are located   7olp_RealEstateAndAccumulatedDepreciationNumberOfStatesInWhichPropertiesContainingCrossDefaultProvisionsLocated
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Number of properties covered by one master lease and one loan secured by cross - collateralized mortgages   11olp_RealEstateAndAccumulatedDepreciationNumberOfPropertiesCoveredByOneMasterLeaseAndOneLoanSecuredByCrossCollateralizedMortgages
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Number of states in which properties covered by one master lease and one loan secured by cross - collateralized mortgages are located   6olp_RealEstateAndAccumulatedDepreciationNumberStatesInWhichPropertiesCoveredByOneMasterLeaseAndOneLoanSecuredByCrossCollateralizedMortgagesLocated
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
   
Real Estate in Ronkonkoma, NY | Flex        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   3,702,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RonkonkomaNYMember
   
Initial Cost To Company        
Land   1,042,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RonkonkomaNYMember
   
Buildings and Improvements   4,171,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RonkonkomaNYMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   1,496,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RonkonkomaNYMember
   
Gross Amount at Which Carried        
Land   1,042,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RonkonkomaNYMember
   
Buildings and Improvements   5,667,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RonkonkomaNYMember
   
Total   6,709,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RonkonkomaNYMember
   
Accumulated Depreciation   1,690,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RonkonkomaNYMember
   
Real Estate 1 in Hauppauge, NY | Flex        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   8,326,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY1Member
   
Initial Cost To Company        
Land   1,952,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY1Member
   
Buildings and Improvements   10,954,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY1Member
   
Gross Amount at Which Carried        
Land   1,952,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY1Member
   
Buildings and Improvements   10,954,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY1Member
   
Total   12,906,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY1Member
   
Accumulated Depreciation   3,845,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY1Member
   
Real Estate 1 in Fort Mill, SC | Flex        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   8,996,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC1Member
   
Initial Cost To Company        
Land   1,840,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC1Member
   
Buildings and Improvements   12,687,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC1Member
   
Gross Amount at Which Carried        
Land   1,840,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC1Member
   
Buildings and Improvements   12,687,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC1Member
   
Total   14,527,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC1Member
   
Accumulated Depreciation   512,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_FlexMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC1Member
   
Real Estate in Tucker, GA | Health Clubs        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   4,968,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TuckerGAMember
   
Initial Cost To Company        
Land   807,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TuckerGAMember
   
Buildings and Improvements   3,027,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TuckerGAMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   3,126,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TuckerGAMember
   
Gross Amount at Which Carried        
Land   807,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TuckerGAMember
   
Buildings and Improvements   6,153,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TuckerGAMember
   
Total   6,960,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TuckerGAMember
   
Accumulated Depreciation   1,775,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TuckerGAMember
   
Real Estate in Hamilton, OH | Health Clubs        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   5,178,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HamiltonOHMember
   
Initial Cost To Company        
Land   1,483,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HamiltonOHMember
   
Buildings and Improvements   5,953,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HamiltonOHMember
   
Gross Amount at Which Carried        
Land   1,483,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HamiltonOHMember
   
Buildings and Improvements   5,953,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HamiltonOHMember
   
Total   7,436,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HamiltonOHMember
   
Accumulated Depreciation   580,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HamiltonOHMember
   
Real Estate in Secaucus, NJ | Health Clubs        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   9,590,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SecaucusNJMember
   
Initial Cost To Company        
Land   5,449,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SecaucusNJMember
   
Buildings and Improvements   9,873,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SecaucusNJMember
   
Gross Amount at Which Carried        
Land   5,449,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SecaucusNJMember
   
Buildings and Improvements   9,873,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SecaucusNJMember
   
Total   15,322,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SecaucusNJMember
   
Accumulated Depreciation   507,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_HealthClubsMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SecaucusNJMember
   
Real Estate 1 in Columbus, OH | Industrial        
Initial Cost To Company        
Land   435,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH1Member
   
Buildings and Improvements   1,703,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH1Member
   
Gross Amount at Which Carried        
Land   435,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH1Member
   
Buildings and Improvements   1,703,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH1Member
   
Total   2,138,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH1Member
   
Accumulated Depreciation   606,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH1Member
   
Real Estate in West Palm Beach, FL | Industrial        
Initial Cost To Company        
Land   181,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestPalmBeachFLMember
   
Buildings and Improvements   724,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestPalmBeachFLMember
   
Gross Amount at Which Carried        
Land   181,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestPalmBeachFLMember
   
Buildings and Improvements   724,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestPalmBeachFLMember
   
Total   905,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestPalmBeachFLMember
   
Accumulated Depreciation   293,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestPalmBeachFLMember
   
Real Estate in New Hyde Park, NY | Industrial        
Initial Cost To Company        
Land   182,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHydeParkNYMember
   
Buildings and Improvements   728,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHydeParkNYMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   33,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHydeParkNYMember
   
Gross Amount at Which Carried        
Land   182,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHydeParkNYMember
   
Buildings and Improvements   761,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHydeParkNYMember
   
Total   943,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHydeParkNYMember
   
Accumulated Depreciation   292,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHydeParkNYMember
   
Real Estate in Melville, NY | Industrial        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   2,982,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MelvilleNYMember
   
Initial Cost To Company        
Land   774,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MelvilleNYMember
   
Buildings and Improvements   3,029,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MelvilleNYMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   975,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MelvilleNYMember
   
Gross Amount at Which Carried        
Land   774,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MelvilleNYMember
   
Buildings and Improvements   4,004,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MelvilleNYMember
   
Total   4,778,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MelvilleNYMember
   
Accumulated Depreciation   998,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MelvilleNYMember
   
Real Estate in Philadelphia, PA | Industrial        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   5,489,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPAMember
   
Initial Cost To Company        
Land   1,981,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPAMember
   
Buildings and Improvements   7,668,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPAMember
   
Gross Amount at Which Carried        
Land   1,981,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPAMember
   
Buildings and Improvements   7,668,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPAMember
   
Total   9,649,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPAMember
   
Accumulated Depreciation   1,893,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPAMember
   
Real Estate in Saco, ME | Industrial        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   3,174,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SacoMEMember
   
Initial Cost To Company        
Land   1,027,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SacoMEMember
   
Buildings and Improvements   3,623,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SacoMEMember
   
Gross Amount at Which Carried        
Land   1,027,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SacoMEMember
   
Buildings and Improvements   3,623,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SacoMEMember
   
Total   4,650,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SacoMEMember
   
Accumulated Depreciation   789,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SacoMEMember
   
Real Estate in Baltimore, MD | Industrial        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   21,114,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BaltimoreMDMember
   
Initial Cost To Company        
Land   6,474,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BaltimoreMDMember
   
Buildings and Improvements   25,282,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BaltimoreMDMember
   
Gross Amount at Which Carried        
Land   6,474,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BaltimoreMDMember
   
Buildings and Improvements   25,282,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BaltimoreMDMember
   
Total   31,756,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BaltimoreMDMember
   
Accumulated Depreciation   5,084,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BaltimoreMDMember
   
Real Estate in Durham, NC | Industrial        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   2,053,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DurhamNCMember
   
Initial Cost To Company        
Land   1,043,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DurhamNCMember
   
Buildings and Improvements   2,404,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DurhamNCMember
   
Gross Amount at Which Carried        
Land   1,043,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DurhamNCMember
   
Buildings and Improvements   2,404,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DurhamNCMember
   
Total   3,447,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DurhamNCMember
   
Accumulated Depreciation   249,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DurhamNCMember
   
Real Estate in Pinellas Park, FL | Industrial        
Initial Cost To Company        
Land   1,231,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PinellasParkFLMember
   
Buildings and Improvements   1,669,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PinellasParkFLMember
   
Gross Amount at Which Carried        
Land   1,231,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PinellasParkFLMember
   
Buildings and Improvements   1,669,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PinellasParkFLMember
   
Total   2,900,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PinellasParkFLMember
   
Accumulated Depreciation   134,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PinellasParkFLMember
   
Real Estate in Miamisburg, OH | Industrial        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   822,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MiamisburgOHMember
   
Initial Cost To Company        
Land   165,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MiamisburgOHMember
   
Buildings and Improvements   1,348,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MiamisburgOHMember
   
Gross Amount at Which Carried        
Land   165,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MiamisburgOHMember
   
Buildings and Improvements   1,348,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MiamisburgOHMember
   
Total   1,513,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MiamisburgOHMember
   
Accumulated Depreciation   80,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MiamisburgOHMember
   
Real Estate in Indianapolis, IN | Industrial        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   6,395,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisINMember
   
Initial Cost To Company        
Land   1,224,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisINMember
   
Buildings and Improvements   6,935,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisINMember
   
Gross Amount at Which Carried        
Land   1,224,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisINMember
   
Buildings and Improvements   6,935,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisINMember
   
Total   8,159,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisINMember
   
Accumulated Depreciation   300,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisINMember
   
Real Estate 2 in Fort Mill, SC | Industrial        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   26,671,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC2Member
   
Initial Cost To Company        
Land   1,804,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC2Member
   
Buildings and Improvements   33,650,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC2Member
   
Gross Amount at Which Carried        
Land   1,804,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC2Member
   
Buildings and Improvements   33,650,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC2Member
   
Total   35,454,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC2Member
   
Accumulated Depreciation   1,543,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FortMillSC2Member
   
Real Estate in New Hope MN | Industrial        
Initial Cost To Company        
Land   881,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHopeMnMember
   
Buildings and Improvements   6,064,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHopeMnMember
   
Gross Amount at Which Carried        
Land   881,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHopeMnMember
   
Buildings and Improvements   6,064,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHopeMnMember
   
Total   6,945,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHopeMnMember
   
Accumulated Depreciation   19,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewHopeMnMember
   
Real Estate in Joppa MD | Industrial        
Initial Cost To Company        
Land   3,805,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_JoppaMdMember
   
Buildings and Improvements   8,142,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_JoppaMdMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   42,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_JoppaMdMember
   
Gross Amount at Which Carried        
Land   3,805,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_JoppaMdMember
   
Buildings and Improvements   8,184,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_JoppaMdMember
   
Total   11,989,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_JoppaMdMember
   
Accumulated Depreciation   115,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_IndustrialPropertyMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_JoppaMdMember
   
Real Estate in Brooklyn, NY | Office        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   5,029,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BrooklynNYMember
   
Initial Cost To Company        
Land   1,381,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BrooklynNYMember
   
Buildings and Improvements   5,447,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BrooklynNYMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   2,870,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BrooklynNYMember
   
Gross Amount at Which Carried        
Land   1,381,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BrooklynNYMember
   
Buildings and Improvements   8,317,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BrooklynNYMember
   
Total   9,698,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BrooklynNYMember
   
Accumulated Depreciation   2,997,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_OfficeBuildingMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BrooklynNYMember
   
Real Estate 1 in Greensboro, NC | Other        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   5,038,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC1Member
   
Initial Cost To Company        
Buildings and Improvements   8,328,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC1Member
   
Gross Amount at Which Carried        
Buildings and Improvements   8,328,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC1Member
   
Total   8,328,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC1Member
   
Accumulated Depreciation   5,567,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC1Member
   
Real Estate in Round Rock, TX | Other        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   14,898,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoundRockTXMember
   
Initial Cost To Company        
Land   1,678,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoundRockTXMember
   
Buildings and Improvements   16,670,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoundRockTXMember
   
Gross Amount at Which Carried        
Land   1,678,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoundRockTXMember
   
Buildings and Improvements   16,670,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoundRockTXMember
   
Total   18,348,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoundRockTXMember
   
Accumulated Depreciation   578,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoundRockTXMember
   
Real Estate in Sandy Springs GA | Other        
Initial Cost To Company        
Land   6,516,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SandySpringsGaMember
   
Gross Amount at Which Carried        
Land   6,516,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SandySpringsGaMember
   
Total   6,516,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SandySpringsGaMember
   
Real Estate 1 in Indianapolis IN | Other        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   4,500,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn1Member
   
Initial Cost To Company        
Land   3,087,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn1Member
   
Buildings and Improvements   5,225,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn1Member
   
Gross Amount at Which Carried        
Land   3,087,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn1Member
   
Buildings and Improvements   5,225,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn1Member
   
Total   8,312,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn1Member
   
Accumulated Depreciation   29,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= olp_OtherRealEstateMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn1Member
   
Real Estate in Seattle, WA | Retail        
Initial Cost To Company        
Land   201,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeattleWAMember
   
Buildings and Improvements   189,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeattleWAMember
   
Gross Amount at Which Carried        
Land   201,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeattleWAMember
   
Buildings and Improvements   189,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeattleWAMember
   
Total   390,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeattleWAMember
   
Accumulated Depreciation   129,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeattleWAMember
   
Real Estate in Rosenberg, TX | Retail        
Initial Cost To Company        
Land   216,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RosenbergTXMember
   
Buildings and Improvements   863,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RosenbergTXMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   67,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RosenbergTXMember
   
Gross Amount at Which Carried        
Land   216,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RosenbergTXMember
   
Buildings and Improvements   930,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RosenbergTXMember
   
Total   1,146,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RosenbergTXMember
   
Accumulated Depreciation   422,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RosenbergTXMember
   
Real Estate in Denver, CO | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   2,801,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DenverCOMember
   
Initial Cost To Company        
Land   780,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DenverCOMember
   
Buildings and Improvements   3,248,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DenverCOMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   418,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DenverCOMember
   
Gross Amount at Which Carried        
Land   780,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DenverCOMember
   
Buildings and Improvements   3,666,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DenverCOMember
   
Total   4,446,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DenverCOMember
   
Accumulated Depreciation   1,598,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DenverCOMember
   
Real Estate in Ft. Myers, FL | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   2,947,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FtMyersFLMember
   
Initial Cost To Company        
Land   1,013,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FtMyersFLMember
   
Buildings and Improvements   4,054,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FtMyersFLMember
   
Gross Amount at Which Carried        
Land   1,013,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FtMyersFLMember
   
Buildings and Improvements   4,054,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FtMyersFLMember
   
Total   5,067,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FtMyersFLMember
   
Accumulated Depreciation   1,837,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FtMyersFLMember
   
Real Estate 2 in Atlanta, GA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,466,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AtlantaGA2Member
   
Initial Cost To Company        
Land   460,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AtlantaGA2Member
   
Buildings and Improvements   2,461,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AtlantaGA2Member
   
Gross Amount at Which Carried        
Land   460,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AtlantaGA2Member
   
Buildings and Improvements   2,461,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AtlantaGA2Member
   
Total   2,921,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AtlantaGA2Member
   
Accumulated Depreciation   1,455,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AtlantaGA2Member
   
Real Estate 1 in Houston, TX | Retail        
Initial Cost To Company        
Land   396,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX1Member
   
Buildings and Improvements   1,583,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX1Member
   
Costs Capitalized Subsequent to Acquisition        
Improvements   30,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX1Member
   
Gross Amount at Which Carried        
Land   396,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX1Member
   
Buildings and Improvements   1,613,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX1Member
   
Total   2,009,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX1Member
   
Accumulated Depreciation   666,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX1Member
   
Real Estate in Selden, NY | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   3,175,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeldenNYMember
   
Initial Cost To Company        
Land   572,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeldenNYMember
   
Buildings and Improvements   2,287,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeldenNYMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   150,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeldenNYMember
   
Gross Amount at Which Carried        
Land   572,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeldenNYMember
   
Buildings and Improvements   2,437,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeldenNYMember
   
Total   3,009,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeldenNYMember
   
Accumulated Depreciation   949,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SeldenNYMember
   
Real Estate in Champaign, IL | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,793,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChampaignILMember
   
Initial Cost To Company        
Land   791,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChampaignILMember
   
Buildings and Improvements   3,165,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChampaignILMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   274,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChampaignILMember
   
Gross Amount at Which Carried        
Land   791,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChampaignILMember
   
Buildings and Improvements   3,439,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChampaignILMember
   
Total   4,230,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChampaignILMember
   
Accumulated Depreciation   1,289,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChampaignILMember
   
Real Estate 1 in El Paso, TX | Retail        
Initial Cost To Company        
Land   2,821,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX1Member
   
Buildings and Improvements   11,123,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX1Member
   
Costs Capitalized Subsequent to Acquisition        
Improvements   321,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX1Member
   
Gross Amount at Which Carried        
Land   2,821,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX1Member
   
Buildings and Improvements   11,444,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX1Member
   
Total   14,265,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX1Member
   
Accumulated Depreciation   4,244,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX1Member
   
Real Estate in Lake Charles, LA | Retail        
Initial Cost To Company        
Land   1,167,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LakeCharlesLAMember
   
Buildings and Improvements   4,669,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LakeCharlesLAMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   521,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LakeCharlesLAMember
   
Gross Amount at Which Carried        
Land   1,167,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LakeCharlesLAMember
   
Buildings and Improvements   5,190,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LakeCharlesLAMember
   
Total   6,357,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LakeCharlesLAMember
   
Accumulated Depreciation   1,495,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LakeCharlesLAMember
   
Real Estate in Somerville, MA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,906,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SomervilleMAMember
   
Initial Cost To Company        
Land   510,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SomervilleMAMember
   
Buildings and Improvements   1,993,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SomervilleMAMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   24,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SomervilleMAMember
   
Gross Amount at Which Carried        
Land   510,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SomervilleMAMember
   
Buildings and Improvements   2,017,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SomervilleMAMember
   
Total   2,527,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SomervilleMAMember
   
Accumulated Depreciation   598,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_SomervilleMAMember
   
Real Estate in Newark, DE | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,934,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewarkDEMember
   
Initial Cost To Company        
Land   935,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewarkDEMember
   
Buildings and Improvements   3,643,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewarkDEMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   10,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewarkDEMember
   
Gross Amount at Which Carried        
Land   935,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewarkDEMember
   
Buildings and Improvements   3,653,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewarkDEMember
   
Total   4,588,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewarkDEMember
   
Accumulated Depreciation   1,037,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewarkDEMember
   
Real Estate in Knoxville, TN | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   3,781,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KnoxvilleTNMember
   
Initial Cost To Company        
Land   2,290,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KnoxvilleTNMember
   
Buildings and Improvements   8,855,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KnoxvilleTNMember
   
Gross Amount at Which Carried        
Land   2,290,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KnoxvilleTNMember
   
Buildings and Improvements   8,855,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KnoxvilleTNMember
   
Total   11,145,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KnoxvilleTNMember
   
Accumulated Depreciation   2,390,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KnoxvilleTNMember
   
Real Estate 1 in Athens, GA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   2,978,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AthensGA1Member
   
Initial Cost To Company        
Land   1,130,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AthensGA1Member
   
Buildings and Improvements   4,340,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AthensGA1Member
   
Gross Amount at Which Carried        
Land   1,130,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AthensGA1Member
   
Buildings and Improvements   4,340,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AthensGA1Member
   
Total   5,470,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AthensGA1Member
   
Accumulated Depreciation   1,153,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AthensGA1Member
   
Real Estate in Onalaska, WI | Retail        
Initial Cost To Company        
Land   753,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_OnalaskaWIMember
   
Buildings and Improvements   3,099,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_OnalaskaWIMember
   
Gross Amount at Which Carried        
Land   753,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_OnalaskaWIMember
   
Buildings and Improvements   3,099,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_OnalaskaWIMember
   
Total   3,852,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_OnalaskaWIMember
   
Accumulated Depreciation   785,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_OnalaskaWIMember
   
Real Estate in Bastrop, LA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   993,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BastropLAMember
   
Initial Cost To Company        
Land   378,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BastropLAMember
   
Buildings and Improvements   1,465,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BastropLAMember
   
Gross Amount at Which Carried        
Land   378,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BastropLAMember
   
Buildings and Improvements   1,465,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BastropLAMember
   
Total   1,843,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BastropLAMember
   
Accumulated Depreciation   297,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BastropLAMember
   
Real Estate in Kentwood, LA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   966,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KentwoodLAMember
   
Initial Cost To Company        
Land   368,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KentwoodLAMember
   
Buildings and Improvements   1,425,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KentwoodLAMember
   
Gross Amount at Which Carried        
Land   368,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KentwoodLAMember
   
Buildings and Improvements   1,425,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KentwoodLAMember
   
Total   1,793,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KentwoodLAMember
   
Accumulated Depreciation   290,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KentwoodLAMember
   
Real Estate 1 in Monroe, LA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   993,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA1Member
   
Initial Cost To Company        
Land   378,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA1Member
   
Buildings and Improvements   1,465,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA1Member
   
Gross Amount at Which Carried        
Land   378,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA1Member
   
Buildings and Improvements   1,465,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA1Member
   
Total   1,843,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA1Member
   
Accumulated Depreciation   297,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA1Member
   
Real Estate 2 in Monroe, LA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   948,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA2Member
   
Initial Cost To Company        
Land   361,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA2Member
   
Buildings and Improvements   1,399,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA2Member
   
Gross Amount at Which Carried        
Land   361,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA2Member
   
Buildings and Improvements   1,399,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA2Member
   
Total   1,760,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA2Member
   
Accumulated Depreciation   284,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroeLA2Member
   
Real Estate in D'lberville, MS | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   966,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DlbervilleMSMember
   
Initial Cost To Company        
Land   368,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DlbervilleMSMember
   
Buildings and Improvements   1,425,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DlbervilleMSMember
   
Gross Amount at Which Carried        
Land   368,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DlbervilleMSMember
   
Buildings and Improvements   1,425,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DlbervilleMSMember
   
Total   1,793,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DlbervilleMSMember
   
Accumulated Depreciation   289,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DlbervilleMSMember
   
Real Estate in Flowood, MS | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,029,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FlowoodMSMember
   
Initial Cost To Company        
Land   392,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FlowoodMSMember
   
Buildings and Improvements   1,517,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FlowoodMSMember
   
Gross Amount at Which Carried        
Land   392,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FlowoodMSMember
   
Buildings and Improvements   1,517,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FlowoodMSMember
   
Total   1,909,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FlowoodMSMember
   
Accumulated Depreciation   308,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FlowoodMSMember
   
Real Estate 1 in Vicksburg, MS | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   940,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS1Member
   
Initial Cost To Company        
Land   358,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS1Member
   
Buildings and Improvements   1,385,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS1Member
   
Gross Amount at Which Carried        
Land   358,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS1Member
   
Buildings and Improvements   1,385,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS1Member
   
Total   1,743,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS1Member
   
Accumulated Depreciation   282,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS1Member
   
Real Estate 2 in Vicksburg, MS | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,145,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS2Member
   
Initial Cost To Company        
Land   436,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS2Member
   
Buildings and Improvements   1,689,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS2Member
   
Gross Amount at Which Carried        
Land   436,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS2Member
   
Buildings and Improvements   1,689,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS2Member
   
Total   2,125,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS2Member
   
Accumulated Depreciation   343,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VicksburgMS2Member
   
Real Estate in Hyannis, MA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   831,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HyannisMAMember
   
Initial Cost To Company        
Land   802,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HyannisMAMember
   
Buildings and Improvements   2,324,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HyannisMAMember
   
Gross Amount at Which Carried        
Land   802,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HyannisMAMember
   
Buildings and Improvements   2,324,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HyannisMAMember
   
Total   3,126,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HyannisMAMember
   
Accumulated Depreciation   404,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HyannisMAMember
   
Real Estate in Marston Mills, MA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   344,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MarstonMillsMAMember
   
Initial Cost To Company        
Land   461,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MarstonMillsMAMember
   
Buildings and Improvements   2,313,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MarstonMillsMAMember
   
Gross Amount at Which Carried        
Land   461,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MarstonMillsMAMember
   
Buildings and Improvements   2,313,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MarstonMillsMAMember
   
Total   2,774,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MarstonMillsMAMember
   
Accumulated Depreciation   397,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MarstonMillsMAMember
   
Real Estate in Everett, MA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,265,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_EverettMAMember
   
Initial Cost To Company        
Land   1,935,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_EverettMAMember
   
Gross Amount at Which Carried        
Land   1,935,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_EverettMAMember
   
Total   1,935,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_EverettMAMember
   
Real Estate in Royersford, PA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   19,750,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoyersfordPAMember
   
Initial Cost To Company        
Land   19,538,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoyersfordPAMember
   
Buildings and Improvements   3,150,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoyersfordPAMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   403,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoyersfordPAMember
   
Gross Amount at Which Carried        
Land   19,538,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoyersfordPAMember
   
Buildings and Improvements   3,553,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoyersfordPAMember
   
Total   23,091,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoyersfordPAMember
   
Accumulated Depreciation   412,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RoyersfordPAMember
   
Real Estate in Monroeville, PA | Retail        
Initial Cost To Company        
Land   450,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroevillePAMember
   
Buildings and Improvements   863,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroevillePAMember
   
Gross Amount at Which Carried        
Land   450,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroevillePAMember
   
Buildings and Improvements   863,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroevillePAMember
   
Total   1,313,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroevillePAMember
   
Accumulated Depreciation   100,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MonroevillePAMember
   
Real Estate in Kansas City, MO | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   4,133,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KansasCityMOMember
   
Initial Cost To Company        
Land   2,958,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KansasCityMOMember
   
Buildings and Improvements   5,691,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KansasCityMOMember
   
Gross Amount at Which Carried        
Land   2,958,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KansasCityMOMember
   
Buildings and Improvements   5,691,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KansasCityMOMember
   
Total   8,649,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KansasCityMOMember
   
Accumulated Depreciation   646,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KansasCityMOMember
   
Real Estate 2 in Houston, TX | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   2,697,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX2Member
   
Initial Cost To Company        
Land   1,962,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX2Member
   
Buildings and Improvements   1,540,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX2Member
   
Gross Amount at Which Carried        
Land   1,962,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX2Member
   
Buildings and Improvements   1,540,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX2Member
   
Total   3,502,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX2Member
   
Accumulated Depreciation   182,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX2Member
   
Real Estate 3 in Houston, TX | Retail        
Initial Cost To Company        
Land   2,002,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX3Member
   
Buildings and Improvements   1,800,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX3Member
   
Gross Amount at Which Carried        
Land   2,002,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX3Member
   
Buildings and Improvements   1,800,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX3Member
   
Total   3,802,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX3Member
   
Accumulated Depreciation   210,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX3Member
   
Real Estate in Bolingbrook, IL | Retail        
Initial Cost To Company        
Land   834,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BolingbrookILMember
   
Buildings and Improvements   1,887,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BolingbrookILMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   90,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BolingbrookILMember
   
Gross Amount at Which Carried        
Land   834,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BolingbrookILMember
   
Buildings and Improvements   1,977,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BolingbrookILMember
   
Total   2,811,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BolingbrookILMember
   
Accumulated Depreciation   187,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BolingbrookILMember
   
Real Estate in Crystal Lake, IL | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,913,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CrystalLakeILMember
   
Initial Cost To Company        
Land   615,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CrystalLakeILMember
   
Buildings and Improvements   1,899,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CrystalLakeILMember
   
Gross Amount at Which Carried        
Land   615,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CrystalLakeILMember
   
Buildings and Improvements   1,899,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CrystalLakeILMember
   
Total   2,514,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CrystalLakeILMember
   
Accumulated Depreciation   207,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CrystalLakeILMember
   
Real Estate in Niles, IL | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   3,245,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NilesILMember
   
Initial Cost To Company        
Land   843,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NilesILMember
   
Buildings and Improvements   3,485,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NilesILMember
   
Gross Amount at Which Carried        
Land   843,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NilesILMember
   
Buildings and Improvements   3,485,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NilesILMember
   
Total   4,328,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NilesILMember
   
Accumulated Depreciation   332,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NilesILMember
   
Real Estate in Lawrence, KS | Retail        
Initial Cost To Company        
Land   134,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrenceKSMember
   
Buildings and Improvements   938,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrenceKSMember
   
Gross Amount at Which Carried        
Land   134,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrenceKSMember
   
Buildings and Improvements   938,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrenceKSMember
   
Total   1,072,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrenceKSMember
   
Accumulated Depreciation   67,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrenceKSMember
   
Real Estate 2 in Greensboro, NC | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,463,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC2Member
   
Initial Cost To Company        
Land   1,046,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC2Member
   
Buildings and Improvements   1,552,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC2Member
   
Costs Capitalized Subsequent to Acquisition        
Improvements   29,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC2Member
   
Gross Amount at Which Carried        
Land   1,046,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC2Member
   
Buildings and Improvements   1,581,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC2Member
   
Total   2,627,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC2Member
   
Accumulated Depreciation   43,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNC2Member
   
Real Estate in Highlands Ranch CO | Retail        
Initial Cost To Company        
Land   2,361,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HighlandsRanchCoMember
   
Buildings and Improvements   2,924,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HighlandsRanchCoMember
   
Gross Amount at Which Carried        
Land   2,361,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HighlandsRanchCoMember
   
Buildings and Improvements   2,924,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HighlandsRanchCoMember
   
Total   5,285,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HighlandsRanchCoMember
   
Accumulated Depreciation   53,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HighlandsRanchCoMember
   
Real Estate in Woodbury MN | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   3,183,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WoodburyMnMember
   
Initial Cost To Company        
Land   1,190,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WoodburyMnMember
   
Buildings and Improvements   4,003,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WoodburyMnMember
   
Gross Amount at Which Carried        
Land   1,190,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WoodburyMnMember
   
Buildings and Improvements   4,003,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WoodburyMnMember
   
Total   5,193,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WoodburyMnMember
   
Accumulated Depreciation   71,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WoodburyMnMember
   
Real Estate in Cape Girardeau, MO | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,336,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CapeGirardeauMOMember
   
Initial Cost To Company        
Land   545,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CapeGirardeauMOMember
   
Buildings and Improvements   1,547,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CapeGirardeauMOMember
   
Gross Amount at Which Carried        
Land   545,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CapeGirardeauMOMember
   
Buildings and Improvements   1,547,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CapeGirardeauMOMember
   
Total   2,092,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CapeGirardeauMOMember
   
Accumulated Depreciation   97,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CapeGirardeauMOMember
   
Real Estate in Cherry Hill, NJ | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   7,389,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CherryHillNJMember
   
Initial Cost To Company        
Land   3,584,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CherryHillNJMember
   
Buildings and Improvements   2,794,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CherryHillNJMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   4,866,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CherryHillNJMember
   
Gross Amount at Which Carried        
Land   3,584,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CherryHillNJMember
   
Buildings and Improvements   7,660,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CherryHillNJMember
   
Total   11,244,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CherryHillNJMember
   
Accumulated Depreciation   1,067,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CherryHillNJMember
   
Real Estate in Clemmons, NC | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   2,410,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ClemmonsNCMember
   
Initial Cost To Company        
Land   2,564,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ClemmonsNCMember
   
Buildings and Improvements   3,293,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ClemmonsNCMember
   
Gross Amount at Which Carried        
Land   2,564,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ClemmonsNCMember
   
Buildings and Improvements   3,293,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ClemmonsNCMember
   
Total   5,857,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ClemmonsNCMember
   
Accumulated Depreciation   210,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ClemmonsNCMember
   
Real Estate in Deptford, NJ | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,924,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DeptfordNJMember
   
Initial Cost To Company        
Land   572,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DeptfordNJMember
   
Buildings and Improvements   1,779,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DeptfordNJMember
   
Costs Capitalized Subsequent to Acquisition        
Improvements   705,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DeptfordNJMember
   
Gross Amount at Which Carried        
Land   572,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DeptfordNJMember
   
Buildings and Improvements   2,484,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DeptfordNJMember
   
Total   3,056,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DeptfordNJMember
   
Accumulated Depreciation   252,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DeptfordNJMember
   
Real Estate 4 in Houston, TX | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   4,844,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX4Member
   
Initial Cost To Company        
Land   3,122,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX4Member
   
Buildings and Improvements   3,767,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX4Member
   
Costs Capitalized Subsequent to Acquisition        
Improvements   52,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX4Member
   
Gross Amount at Which Carried        
Land   3,122,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX4Member
   
Buildings and Improvements   3,819,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX4Member
   
Total   6,941,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX4Member
   
Accumulated Depreciation   321,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HoustonTX4Member
   
Real Estate 2 in Hauppauge, NY | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,910,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY2Member
   
Initial Cost To Company        
Land   725,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY2Member
   
Buildings and Improvements   2,963,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY2Member
   
Gross Amount at Which Carried        
Land   725,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY2Member
   
Buildings and Improvements   2,963,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY2Member
   
Total   3,688,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY2Member
   
Accumulated Depreciation   676,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HauppaugeNY2Member
   
Real Estate in Palmyra, PA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   797,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PalmyraPAMember
   
Initial Cost To Company        
Land   650,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PalmyraPAMember
   
Buildings and Improvements   650,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PalmyraPAMember
   
Gross Amount at Which Carried        
Land   650,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PalmyraPAMember
   
Buildings and Improvements   650,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PalmyraPAMember
   
Total   1,300,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PalmyraPAMember
   
Accumulated Depreciation   72,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PalmyraPAMember
   
Real Estate 1 in Reading, PA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   787,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA1Member
   
Initial Cost To Company        
Land   655,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA1Member
   
Buildings and Improvements   625,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA1Member
   
Gross Amount at Which Carried        
Land   655,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA1Member
   
Buildings and Improvements   625,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA1Member
   
Total   1,280,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA1Member
   
Accumulated Depreciation   70,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA1Member
   
Real Estate 2 in Reading, PA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   775,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA2Member
   
Initial Cost To Company        
Land   618,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA2Member
   
Buildings and Improvements   643,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA2Member
   
Gross Amount at Which Carried        
Land   618,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA2Member
   
Buildings and Improvements   643,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA2Member
   
Total   1,261,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA2Member
   
Accumulated Depreciation   73,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ReadingPA2Member
   
Real Estate in Hanover, PA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   871,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HanoverPAMember
   
Initial Cost To Company        
Land   736,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HanoverPAMember
   
Buildings and Improvements   686,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HanoverPAMember
   
Gross Amount at Which Carried        
Land   736,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HanoverPAMember
   
Buildings and Improvements   686,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HanoverPAMember
   
Total   1,422,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HanoverPAMember
   
Accumulated Depreciation   75,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_HanoverPAMember
   
Real Estate in Gettysburg, PA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   893,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GettysburgPAMember
   
Initial Cost To Company        
Land   754,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GettysburgPAMember
   
Buildings and Improvements   704,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GettysburgPAMember
   
Gross Amount at Which Carried        
Land   754,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GettysburgPAMember
   
Buildings and Improvements   704,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GettysburgPAMember
   
Total   1,458,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GettysburgPAMember
   
Accumulated Depreciation   77,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GettysburgPAMember
   
Real Estate in Trexlertown, PA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   759,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TrexlertownPAMember
   
Initial Cost To Company        
Land   800,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TrexlertownPAMember
   
Buildings and Improvements   439,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TrexlertownPAMember
   
Gross Amount at Which Carried        
Land   800,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TrexlertownPAMember
   
Buildings and Improvements   439,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TrexlertownPAMember
   
Total   1,239,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TrexlertownPAMember
   
Accumulated Depreciation   48,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TrexlertownPAMember
   
Real Estate in Island Park, NY | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,047,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IslandParkNYMember
   
Initial Cost To Company        
Land   1,235,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IslandParkNYMember
   
Buildings and Improvements   1,355,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IslandParkNYMember
   
Gross Amount at Which Carried        
Land   1,235,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IslandParkNYMember
   
Buildings and Improvements   1,355,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IslandParkNYMember
   
Total   2,590,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IslandParkNYMember
   
Accumulated Depreciation   164,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IslandParkNYMember
   
Real Estate in Carrollton, GA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,698,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CarrolltonGAMember
   
Initial Cost To Company        
Land   796,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CarrolltonGAMember
   
Buildings and Improvements   1,458,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CarrolltonGAMember
   
Gross Amount at Which Carried        
Land   796,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CarrolltonGAMember
   
Buildings and Improvements   1,458,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CarrolltonGAMember
   
Total   2,254,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CarrolltonGAMember
   
Accumulated Depreciation   120,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CarrolltonGAMember
   
Real Estate in Cartersville, GA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,606,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CartersvilleGAMember
   
Initial Cost To Company        
Land   786,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CartersvilleGAMember
   
Buildings and Improvements   1,346,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CartersvilleGAMember
   
Gross Amount at Which Carried        
Land   786,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CartersvilleGAMember
   
Buildings and Improvements   1,346,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CartersvilleGAMember
   
Total   2,132,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CartersvilleGAMember
   
Accumulated Depreciation   118,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CartersvilleGAMember
   
Real Estate 1 in Kennesaw, GA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,316,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA1Member
   
Initial Cost To Company        
Land   702,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA1Member
   
Buildings and Improvements   916,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA1Member
   
Gross Amount at Which Carried        
Land   702,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA1Member
   
Buildings and Improvements   916,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA1Member
   
Total   1,618,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA1Member
   
Accumulated Depreciation   80,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA1Member
   
Real Estate in Lawrenceville, GA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,263,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrencevilleGAMember
   
Initial Cost To Company        
Land   866,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrencevilleGAMember
   
Buildings and Improvements   899,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrencevilleGAMember
   
Gross Amount at Which Carried        
Land   866,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrencevilleGAMember
   
Buildings and Improvements   899,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrencevilleGAMember
   
Total   1,765,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrencevilleGAMember
   
Accumulated Depreciation   100,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LawrencevilleGAMember
   
Real Estate in Killeen, TX | Retail        
Initial Cost To Company        
Land   1,265,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KilleenTXMember
   
Buildings and Improvements   803,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KilleenTXMember
   
Gross Amount at Which Carried        
Land   1,265,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KilleenTXMember
   
Buildings and Improvements   803,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KilleenTXMember
   
Total   2,068,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KilleenTXMember
   
Accumulated Depreciation   50,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KilleenTXMember
   
Real Estate in Concord, NC | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,647,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ConcordNCMember
   
Initial Cost To Company        
Land   999,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ConcordNCMember
   
Buildings and Improvements   1,076,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ConcordNCMember
   
Gross Amount at Which Carried        
Land   999,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ConcordNCMember
   
Buildings and Improvements   1,076,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ConcordNCMember
   
Total   2,075,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ConcordNCMember
   
Accumulated Depreciation   45,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ConcordNCMember
   
Real Estate in Myrtle Beach, SC | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,647,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MyrtleBeachSCMember
   
Initial Cost To Company        
Land   1,102,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MyrtleBeachSCMember
   
Buildings and Improvements   1,161,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MyrtleBeachSCMember
   
Gross Amount at Which Carried        
Land   1,102,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MyrtleBeachSCMember
   
Buildings and Improvements   1,161,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MyrtleBeachSCMember
   
Total   2,263,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MyrtleBeachSCMember
   
Accumulated Depreciation   48,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_MyrtleBeachSCMember
   
Real Estate in Ann Arbor, MI | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,462,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AnnArborMIMember
   
Initial Cost To Company        
Land   1,098,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AnnArborMIMember
   
Buildings and Improvements   1,460,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AnnArborMIMember
   
Gross Amount at Which Carried        
Land   1,098,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AnnArborMIMember
   
Buildings and Improvements   1,460,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AnnArborMIMember
   
Total   2,558,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AnnArborMIMember
   
Accumulated Depreciation   63,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AnnArborMIMember
   
Real Estate in Greensboro, NC | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   3,488,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNCMember
   
Initial Cost To Company        
Land   1,770,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNCMember
   
Buildings and Improvements   1,237,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNCMember
   
Gross Amount at Which Carried        
Land   1,770,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNCMember
   
Buildings and Improvements   1,237,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNCMember
   
Total   3,007,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNCMember
   
Accumulated Depreciation   40,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GreensboroNCMember
   
Real Estate 1 in Richmond, VA | Retail        
Initial Cost To Company        
Land   1,680,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA1Member
   
Buildings and Improvements   1,341,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA1Member
   
Gross Amount at Which Carried        
Land   1,680,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA1Member
   
Buildings and Improvements   1,341,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA1Member
   
Total   3,021,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA1Member
   
Accumulated Depreciation   42,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA1Member
   
Real Estate 2 in Indianapolis IN | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   996,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn2Member
   
Initial Cost To Company        
Land   853,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn2Member
   
Buildings and Improvements   1,465,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn2Member
   
Gross Amount at Which Carried        
Land   853,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn2Member
   
Buildings and Improvements   1,465,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn2Member
   
Total   2,318,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn2Member
   
Accumulated Depreciation   41,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_IndianapolisIn2Member
   
Real Estate 1 in West Hartford, CT | Retail        
Initial Cost To Company        
Land   2,881,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT1Member
   
Buildings and Improvements   94,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT1Member
   
Costs Capitalized Subsequent to Acquisition        
Improvements   326,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT1Member
   
Gross Amount at Which Carried        
Land   2,881,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT1Member
   
Buildings and Improvements   420,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT1Member
   
Total   3,301,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT1Member
   
Accumulated Depreciation   61,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT1Member
   
Real Estate 2 in West Hartford, CT | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   12,427,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT2Member
   
Initial Cost To Company        
Land   9,296,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT2Member
   
Buildings and Improvements   4,813,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT2Member
   
Costs Capitalized Subsequent to Acquisition        
Improvements   261,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT2Member
   
Gross Amount at Which Carried        
Land   9,296,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT2Member
   
Buildings and Improvements   5,074,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT2Member
   
Total   14,370,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT2Member
   
Accumulated Depreciation   615,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WestHartfordCT2Member
   
Real Estate 1 in Philadelphia PA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   4,626,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPa1Member
   
Initial Cost To Company        
Land   1,793,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPa1Member
   
Buildings and Improvements   5,640,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPa1Member
   
Gross Amount at Which Carried        
Land   1,793,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPa1Member
   
Buildings and Improvements   5,640,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPa1Member
   
Total   7,433,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPa1Member
   
Accumulated Depreciation   32,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_PhiladelphiaPa1Member
   
Real Estate 2 in Columbus, OH | Retail        
Initial Cost To Company        
Land   1,445,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH2Member
   
Buildings and Improvements   5,431,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH2Member
   
Costs Capitalized Subsequent to Acquisition        
Improvements   350,000us-gaap_RealEstateAndAccumulatedDepreciationCostsCapitalizedSubsequentToAcquisitionImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH2Member
   
Gross Amount at Which Carried        
Land   1,445,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH2Member
   
Buildings and Improvements   5,781,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH2Member
   
Total   7,226,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH2Member
   
Accumulated Depreciation   2,475,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ColumbusOH2Member
   
Real Estate in Duluth, GA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,757,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DuluthGAMember
   
Initial Cost To Company        
Land   778,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DuluthGAMember
   
Buildings and Improvements   3,436,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DuluthGAMember
   
Gross Amount at Which Carried        
Land   778,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DuluthGAMember
   
Buildings and Improvements   3,436,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DuluthGAMember
   
Total   4,214,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DuluthGAMember
   
Accumulated Depreciation   748,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_DuluthGAMember
   
Real Estate in Fayetteville, GA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   2,204,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FayettevilleGAMember
   
Initial Cost To Company        
Land   976,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FayettevilleGAMember
   
Buildings and Improvements   4,308,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FayettevilleGAMember
   
Gross Amount at Which Carried        
Land   976,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FayettevilleGAMember
   
Buildings and Improvements   4,308,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FayettevilleGAMember
   
Total   5,284,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FayettevilleGAMember
   
Accumulated Depreciation   938,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_FayettevilleGAMember
   
Real Estate in Wichita, KS | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   2,684,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WichitaKSMember
   
Initial Cost To Company        
Land   1,189,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WichitaKSMember
   
Buildings and Improvements   5,248,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WichitaKSMember
   
Gross Amount at Which Carried        
Land   1,189,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WichitaKSMember
   
Buildings and Improvements   5,248,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WichitaKSMember
   
Total   6,437,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WichitaKSMember
   
Accumulated Depreciation   1,143,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_WichitaKSMember
   
Real Estate in Lexington, KY | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,806,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LexingtonKYMember
   
Initial Cost To Company        
Land   800,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LexingtonKYMember
   
Buildings and Improvements   3,532,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LexingtonKYMember
   
Gross Amount at Which Carried        
Land   800,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LexingtonKYMember
   
Buildings and Improvements   3,532,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LexingtonKYMember
   
Total   4,332,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LexingtonKYMember
   
Accumulated Depreciation   769,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_LexingtonKYMember
   
Real Estate in Bluffton, SC | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,330,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BlufftonSCMember
   
Initial Cost To Company        
Land   589,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BlufftonSCMember
   
Buildings and Improvements   2,600,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BlufftonSCMember
   
Gross Amount at Which Carried        
Land   589,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BlufftonSCMember
   
Buildings and Improvements   2,600,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BlufftonSCMember
   
Total   3,189,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BlufftonSCMember
   
Accumulated Depreciation   566,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BlufftonSCMember
   
Real Estate in Amarillo, TX | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,948,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AmarilloTXMember
   
Initial Cost To Company        
Land   863,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AmarilloTXMember
   
Buildings and Improvements   3,810,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AmarilloTXMember
   
Gross Amount at Which Carried        
Land   863,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AmarilloTXMember
   
Buildings and Improvements   3,810,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AmarilloTXMember
   
Total   4,673,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AmarilloTXMember
   
Accumulated Depreciation   830,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AmarilloTXMember
   
Real Estate in Austin, TX | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   3,583,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AustinTXMember
   
Initial Cost To Company        
Land   1,587,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AustinTXMember
   
Buildings and Improvements   7,010,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AustinTXMember
   
Gross Amount at Which Carried        
Land   1,587,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AustinTXMember
   
Buildings and Improvements   7,010,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AustinTXMember
   
Total   8,597,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AustinTXMember
   
Accumulated Depreciation   1,526,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_AustinTXMember
   
Real Estate in Tyler, TX | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   2,328,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TylerTXMember
   
Initial Cost To Company        
Land   1,031,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TylerTXMember
   
Buildings and Improvements   4,554,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TylerTXMember
   
Gross Amount at Which Carried        
Land   1,031,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TylerTXMember
   
Buildings and Improvements   4,554,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TylerTXMember
   
Total   5,585,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TylerTXMember
   
Accumulated Depreciation   991,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_TylerTXMember
   
Real Estate in Newport News, VA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,696,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewportNewsVAMember
   
Initial Cost To Company        
Land   751,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewportNewsVAMember
   
Buildings and Improvements   3,316,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewportNewsVAMember
   
Gross Amount at Which Carried        
Land   751,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewportNewsVAMember
   
Buildings and Improvements   3,316,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewportNewsVAMember
   
Total   4,067,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewportNewsVAMember
   
Accumulated Depreciation   722,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NewportNewsVAMember
   
Real Estate 2 in Richmond, VA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,957,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA2Member
   
Initial Cost To Company        
Land   867,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA2Member
   
Buildings and Improvements   3,829,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA2Member
   
Gross Amount at Which Carried        
Land   867,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA2Member
   
Buildings and Improvements   3,829,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA2Member
   
Total   4,696,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA2Member
   
Accumulated Depreciation   833,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_RichmondVA2Member
   
Real Estate in Virginia Beach, VA | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   1,928,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VirginiaBeachVAMember
   
Initial Cost To Company        
Land   854,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VirginiaBeachVAMember
   
Buildings and Improvements   3,770,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VirginiaBeachVAMember
   
Gross Amount at Which Carried        
Land   854,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VirginiaBeachVAMember
   
Buildings and Improvements   3,770,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VirginiaBeachVAMember
   
Total   4,624,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VirginiaBeachVAMember
   
Accumulated Depreciation   821,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_VirginiaBeachVAMember
   
Real Estate in Gurnee, IL | Retail        
Schedule III - Consolidated Real Estate and Accumulated Depreciation        
Encumbrances   2,398,000us-gaap_RealEstateAndAccumulatedDepreciationAmountOfEncumbrances
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GurneeILMember
   
Initial Cost To Company        
Land   834,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GurneeILMember
   
Buildings and Improvements   3,635,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GurneeILMember
   
Gross Amount at Which Carried        
Land   834,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GurneeILMember
   
Buildings and Improvements   3,635,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GurneeILMember
   
Total   4,469,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GurneeILMember
   
Accumulated Depreciation   753,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_GurneeILMember
   
Real Estate in Naples, FL | Retail        
Initial Cost To Company        
Land   3,070,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NaplesFLMember
   
Buildings and Improvements   2,846,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NaplesFLMember
   
Gross Amount at Which Carried        
Land   3,070,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NaplesFLMember
   
Buildings and Improvements   2,846,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NaplesFLMember
   
Total   5,916,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NaplesFLMember
   
Accumulated Depreciation   448,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_NaplesFLMember
   
Real Estate in Batavia, NY | Retail        
Initial Cost To Company        
Land   515,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BataviaNYMember
   
Buildings and Improvements   2,061,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BataviaNYMember
   
Gross Amount at Which Carried        
Land   515,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BataviaNYMember
   
Buildings and Improvements   2,061,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BataviaNYMember
   
Total   2,576,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BataviaNYMember
   
Accumulated Depreciation   818,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_BataviaNYMember
   
Real Estate 2 in Kennesaw, GA | Retail        
Initial Cost To Company        
Land   1,501,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA2Member
   
Buildings and Improvements   4,349,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA2Member
   
Gross Amount at Which Carried        
Land   1,501,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA2Member
   
Buildings and Improvements   4,349,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA2Member
   
Total   5,850,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA2Member
   
Accumulated Depreciation   684,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_KennesawGA2Member
   
Real Estate in Chicago, IL | Retail        
Initial Cost To Company        
Land   3,877,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChicagoILMember
   
Buildings and Improvements   2,256,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChicagoILMember
   
Gross Amount at Which Carried        
Land   3,877,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChicagoILMember
   
Buildings and Improvements   2,256,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChicagoILMember
   
Total   6,133,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChicagoILMember
   
Accumulated Depreciation   355,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ChicagoILMember
   
Real Estate in Cary, NC | Retail        
Initial Cost To Company        
Land   1,129,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CaryNCMember
   
Buildings and Improvements   3,736,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CaryNCMember
   
Gross Amount at Which Carried        
Land   1,129,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CaryNCMember
   
Buildings and Improvements   3,736,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CaryNCMember
   
Total   4,865,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CaryNCMember
   
Accumulated Depreciation   588,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_CaryNCMember
   
Real Estate in Eugene, OR | Retail        
Initial Cost To Company        
Land   1,952,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_EugeneORMember
   
Buildings and Improvements   2,096,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_EugeneORMember
   
Gross Amount at Which Carried        
Land   1,952,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_EugeneORMember
   
Buildings and Improvements   2,096,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_EugeneORMember
   
Total   4,048,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_EugeneORMember
   
Accumulated Depreciation   330,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_EugeneORMember
   
Real Estate 2 in El Paso, TX | Retail        
Initial Cost To Company        
Land   1,035,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX2Member
   
Buildings and Improvements   2,700,000us-gaap_RealEstateAndAccumulatedDepreciationInitialCostOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX2Member
   
Gross Amount at Which Carried        
Land   1,035,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfLand
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX2Member
   
Buildings and Improvements   2,700,000us-gaap_RealEstateAndAccumulatedDepreciationCarryingAmountOfBuildingsAndImprovements
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX2Member
   
Total   3,735,000us-gaap_RealEstateGrossAtCarryingValue
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX2Member
   
Accumulated Depreciation   425,000us-gaap_RealEstateAccumulatedDepreciation
/ us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis
= us-gaap_RetailSiteMember
/ us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis
= olp_ElPasoTX2Member