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REAL ESTATE INVESTMENTS AND MINIMUM FUTURE RENTALS (Details) (USD $) | 12 Months Ended | 0 Months Ended
--- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Feb. 25, 2015 item
Real Estate Acquisitions |  |  |  |
Third Party Real Estate Acquisition Costs | $ 479,000 olp_CostsOfAcquiringRealEstate | $ 921,000 olp_CostsOfAcquiringRealEstate | $ 823,000 olp_CostsOfAcquiringRealEstate |
Contributions from non-controlling interests | 639,000 us-gaap_NoncontrollingInterestIncreaseFromBusinessCombination | 480,000 us-gaap_NoncontrollingInterestIncreaseFromBusinessCombination | 571,000 us-gaap_NoncontrollingInterestIncreaseFromBusinessCombination |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 21,606,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand | 16,951,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand |  |
Building | 33,590,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings | 75,915,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings |  |
Building Improvements | 1,511,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements | 4,312,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements |  |
Intangible Lease Asset | 4,771,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles | 11,624,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles |  |
Intangible Lease Liability | (4,376,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability | (2,210,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability |  |
Total | 57,102,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet | 106,592,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet |  |
Intangible Lease Liability | (4,376,000)olp_BelowMarketLeaseAcquiredAfterAdjustments |  |  |
Restricted cash | 1,607,000 us-gaap_RestrictedCashAndCashEquivalents |  |  |
Occupancy percentage for properties purchased by the company | 100.00%olp_RealEstatePropertiesAcquisitionOccupancyPercentage |  |  |
Weighted average amortization period for intangible lease liabilities | 9 years 1 month 6 days | 5 years 10 months 24 days |  |
Below market lease accumulated amortization | 3,928,000 us-gaap_BelowMarketLeaseAccumulatedAmortization | 3,099,000 us-gaap_BelowMarketLeaseAccumulatedAmortization |  |
Net increase (decrease) in rental revenue due to amortization of the above/below market leases | 267,000 us-gaap_AmortizationOfAboveAndBelowMarketLeases | 160,000 us-gaap_AmortizationOfAboveAndBelowMarketLeases | (2,000)us-gaap_AmortizationOfAboveAndBelowMarketLeases |
Minimum future contractual rents to be received |  |  |  |
2015 | 53,345,000 us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableCurrent |  |  |
2016 | 50,916,000 us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInTwoYears |  |  |
2017 | 48,176,000 us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInThreeYears |  |  |
2018 | 45,803,000 us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInFourYears |  |  |
2019 | 41,338,000 us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableInFiveYears |  |  |
Thereafter | 217,547,000 us-gaap_OperatingLeasesFutureMinimumPaymentsReceivableThereafter |  |  |
Total | 457,125,000 us-gaap_OperatingLeasesFutureMinimumPaymentsReceivable |  |  |
Unbilled Rent Receivable |  |  |  |
Unbilled rent receivables | 12,815,000 us-gaap_DeferredRentReceivablesNet | 13,743,000 us-gaap_DeferredRentReceivablesNet |  |
Period during which amount of unbilled rent receivable is to be billed and received | 30 years |  |  |
Unbilled straight-line rent receivable written off | 2,417,000 olp_DeferredRentReceivableWrittenOff |  |  |
Rental income |  |  |  |
Future amortization income of below market leases |  |  |  |
2015 | 982,000 us-gaap_BelowMarketLeaseAmortizationIncomeNextTwelveMonths / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
2016 | 967,000 us-gaap_BelowMarketLeaseAmortizationIncomeYearTwo / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
2017 | 958,000 us-gaap_BelowMarketLeaseAmortizationIncomeYearThree / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
2018 | 835,000 us-gaap_BelowMarketLeaseAmortizationIncomeYearFour / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
2019 | 789,000 us-gaap_BelowMarketLeaseAmortizationIncomeYearFive / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
Thereafter | 5,932,000 us-gaap_BelowMarketLeaseAmortizationIncomeAfterYearFive / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
Total | 10,463,000 us-gaap_BelowMarketLeaseNet / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
Intangible lease asset - above market lease | Rental income |  |  |  |
Amortization of intangible lease assets |  |  |  |
2015 | 468,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
2016 | 453,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
2017 | 413,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
2018 | 348,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
2019 | 263,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
Thereafter | 1,634,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
Total | 3,579,000 us-gaap_FiniteLivedIntangibleAssetsNet / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_AboveMarketLeasesMember / us-gaap_IncomeStatementLocationAxis = olp_RentalRevenueMember |  |  |
Intangible lease asset |  |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Intangible lease assets | 4,771,000 us-gaap_FinitelivedIntangibleAssetsAcquired1 / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember | 11,624,000 us-gaap_FinitelivedIntangibleAssetsAcquired1 / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember |  |
Weighted average amortization period for intangible lease assets | 9 years 3 months 18 days | 13 years 2 months 12 days |  |
Above market lease accumulated amortization | 9,170,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember | 7,054,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember |  |
Intangible lease asset | Amortization expense |  |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Amortization expense relating to origination costs | 2,430,000 us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember / us-gaap_IncomeStatementLocationAxis = olp_AmortizationExpenseMember | 1,647,000 us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember / us-gaap_IncomeStatementLocationAxis = olp_AmortizationExpenseMember | 1,006,000 us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember / us-gaap_IncomeStatementLocationAxis = olp_AmortizationExpenseMember |
Amortization of intangible lease assets |  |  |  |
2015 | 2,594,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember / us-gaap_IncomeStatementLocationAxis = olp_AmortizationExpenseMember |  |  |
2016 | 2,480,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember / us-gaap_IncomeStatementLocationAxis = olp_AmortizationExpenseMember |  |  |
2017 | 2,387,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember / us-gaap_IncomeStatementLocationAxis = olp_AmortizationExpenseMember |  |  |
2018 | 2,238,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember / us-gaap_IncomeStatementLocationAxis = olp_AmortizationExpenseMember |  |  |
2019 | 2,073,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember / us-gaap_IncomeStatementLocationAxis = olp_AmortizationExpenseMember |  |  |
Thereafter | 12,036,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember / us-gaap_IncomeStatementLocationAxis = olp_AmortizationExpenseMember |  |  |
Total | 23,808,000 us-gaap_FiniteLivedIntangibleAssetsNet / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = olp_LeasesAcquiredInPlaceExcludingBelowMarketLeaseMember / us-gaap_IncomeStatementLocationAxis = olp_AmortizationExpenseMember |  |  |
Consolidated JV | Minimum |  |  |  |
Real Estate Acquisitions |  |  |  |
Ownership interest in consolidated joint venture of the company (as a percent) | 85.00%us-gaap_MinorityInterestOwnershipPercentageByParent / us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis = olp_ConsolidatedJointVentureMember / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |
Subtotals |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price | 56,793,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember | 107,529,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember |  |
Third Party Real Estate Acquisition Costs | 479,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember | 921,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 21,532,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember | 16,951,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember |  |
Building | 33,520,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember | 75,915,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember |  |
Building Improvements | 1,493,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember | 4,312,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember |  |
Intangible Lease Asset | 4,830,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember | 12,575,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember |  |
Intangible Lease Liability | (4,279,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember | (2,174,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember |  |
Total | 57,096,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember | 107,579,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_CurrentFiscalYearRealEstateAcquisitionsMember |  |
Other |  |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 74,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_PriorFiscalYearRealEstateAcquisitionsMember |  |  |
Building | 70,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_PriorFiscalYearRealEstateAcquisitionsMember |  |  |
Building Improvements | 18,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_PriorFiscalYearRealEstateAcquisitionsMember |  |  |
Total | 6,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_PriorFiscalYearRealEstateAcquisitionsMember | (987,000)us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_PriorFiscalYearRealEstateAcquisitionsMember |  |
Other | (59,000)olp_BusinessCombinationAdjustmentsToIntangibleLeaseAssets / us-gaap_BusinessAcquisitionAxis = olp_PriorFiscalYearRealEstateAcquisitionsMember | (951,000)olp_BusinessCombinationAdjustmentsToIntangibleLeaseAssets / us-gaap_BusinessAcquisitionAxis = olp_PriorFiscalYearRealEstateAcquisitionsMember |  |
Other | (97,000)olp_BusinessCombinationAdjustmentsToIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_PriorFiscalYearRealEstateAcquisitionsMember | (36,000)olp_BusinessCombinationAdjustmentsToIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_PriorFiscalYearRealEstateAcquisitionsMember |  |
Total Wine and More Retail Store, Greensboro, North Carolina [Member] |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price | 2,971,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_TotalWineAndMoreRetailStoreGreensboroNorthCarolinaMember |  |  |
Third Party Real Estate Acquisition Costs | 20,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_TotalWineAndMoreRetailStoreGreensboroNorthCarolinaMember |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 1,046,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_TotalWineAndMoreRetailStoreGreensboroNorthCarolinaMember |  |  |
Building | 1,468,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_TotalWineAndMoreRetailStoreGreensboroNorthCarolinaMember |  |  |
Building Improvements | 83,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_TotalWineAndMoreRetailStoreGreensboroNorthCarolinaMember |  |  |
Intangible Lease Asset | 374,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_TotalWineAndMoreRetailStoreGreensboroNorthCarolinaMember |  |  |
Total | 2,971,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_TotalWineAndMoreRetailStoreGreensboroNorthCarolinaMember |  |  |
Chuck E Cheese Restaurant Indianapolis Indiana [Member] |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price | 2,138,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_ChuckECheeseRestaurantIndianapolisIndianaMember |  |  |
Third Party Real Estate Acquisition Costs | 10,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_ChuckECheeseRestaurantIndianapolisIndianaMember |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 853,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_ChuckECheeseRestaurantIndianapolisIndianaMember |  |  |
Building | 1,321,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_ChuckECheeseRestaurantIndianapolisIndianaMember |  |  |
Building Improvements | 145,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_ChuckECheeseRestaurantIndianapolisIndianaMember |  |  |
Intangible Lease Asset | 94,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_ChuckECheeseRestaurantIndianapolisIndianaMember |  |  |
Intangible Lease Liability | (275,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_ChuckECheeseRestaurantIndianapolisIndianaMember |  |  |
Total | 2,138,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_ChuckECheeseRestaurantIndianapolisIndianaMember |  |  |
Savers Thrift Superstore Highlands Ranch Colorado [Member] |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price | 4,825,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_SaversThriftSuperstoreHighlandsRanchColoradoMember |  |  |
Third Party Real Estate Acquisition Costs | 83,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_SaversThriftSuperstoreHighlandsRanchColoradoMember |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 2,361,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_SaversThriftSuperstoreHighlandsRanchColoradoMember |  |  |
Building | 2,644,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_SaversThriftSuperstoreHighlandsRanchColoradoMember |  |  |
Building Improvements | 280,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_SaversThriftSuperstoreHighlandsRanchColoradoMember |  |  |
Intangible Lease Asset | 856,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_SaversThriftSuperstoreHighlandsRanchColoradoMember |  |  |
Intangible Lease Liability | (1,316,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_SaversThriftSuperstoreHighlandsRanchColoradoMember |  |  |
Total | 4,825,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_SaversThriftSuperstoreHighlandsRanchColoradoMember |  |  |
Hobby Lobby Retail Store Woodbury Minnesota [Member] |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price | 4,770,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_HobbyLobbyRetailStoreWoodburyMinnesotaMember |  |  |
Third Party Real Estate Acquisition Costs | 46,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_HobbyLobbyRetailStoreWoodburyMinnesotaMember |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 1,190,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_HobbyLobbyRetailStoreWoodburyMinnesotaMember |  |  |
Building | 3,667,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_HobbyLobbyRetailStoreWoodburyMinnesotaMember |  |  |
Building Improvements | 335,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_HobbyLobbyRetailStoreWoodburyMinnesotaMember |  |  |
Intangible Lease Asset | 734,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_HobbyLobbyRetailStoreWoodburyMinnesotaMember |  |  |
Intangible Lease Liability | (1,156,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_HobbyLobbyRetailStoreWoodburyMinnesotaMember |  |  |
Total | 4,770,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_HobbyLobbyRetailStoreWoodburyMinnesotaMember |  |  |
Land River Crossing Apartments Sandy Spring Georgia [Member] |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price | 6,510,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_LandRiverCrossingApartmentsSandySpringGeorgiaMember |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 6,516,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_LandRiverCrossingApartmentsSandySpringGeorgiaMember |  |  |
Total | 6,516,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_LandRiverCrossingApartmentsSandySpringGeorgiaMember |  |  |
Capitalized transaction costs incurred with the asset acquisition | 6,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = olp_LandRiverCrossingApartmentsSandySpringGeorgiaMember |  |  |
Amount of mortgage to owner/operator | 16,230,000 olp_BusinessCombinationConsiderationTransferredAsMortgageDebt / us-gaap_BusinessAcquisitionAxis = olp_LandRiverCrossingApartmentsSandySpringGeorgiaMember |  |  |
Land River Crossing Apartments Sandy Springs Georgia and Noxell Corporation Industrial Building Joppa Maryland [Member] |  |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Capitalized transaction costs incurred with the asset acquisition | 303,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = olp_LandRiverCrossingApartmentsSandySpringsGeorgiaAndNoxellCorporationIndustrialBuildingJoppaMarylandMember |  |  |
Noxel Corporation Industrial Building Joppa Maryland [Member] |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price | 11,650,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_NoxelCorporationIndustrialBuildingJoppaMarylandMember |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 3,805,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_NoxelCorporationIndustrialBuildingJoppaMarylandMember |  |  |
Building | 7,991,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_NoxelCorporationIndustrialBuildingJoppaMarylandMember |  |  |
Building Improvements | 151,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_NoxelCorporationIndustrialBuildingJoppaMarylandMember |  |  |
Total | 11,947,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_NoxelCorporationIndustrialBuildingJoppaMarylandMember |  |  |
Capitalized transaction costs incurred with the asset acquisition | 297,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = olp_NoxelCorporationIndustrialBuildingJoppaMarylandMember |  |  |
Noxel Corporation Industrial Building Joppa Maryland [Member] | Consolidated JV |  |  |  |
Real Estate Acquisitions |  |  |  |
Ownership interest in consolidated joint venture of the company (as a percent) | 95.00%us-gaap_MinorityInterestOwnershipPercentageByParent / us-gaap_BusinessAcquisitionAxis = olp_NoxelCorporationIndustrialBuildingJoppaMarylandMember / us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis = olp_ConsolidatedJointVentureMember |  |  |
Ownership interest in consolidated joint venture of non-controlling interest (as a percent) | 5.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / us-gaap_BusinessAcquisitionAxis = olp_NoxelCorporationIndustrialBuildingJoppaMarylandMember / us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis = olp_ConsolidatedJointVentureMember |  |  |
Contributions from non-controlling interests | 306,000 us-gaap_NoncontrollingInterestIncreaseFromBusinessCombination / us-gaap_BusinessAcquisitionAxis = olp_NoxelCorporationIndustrialBuildingJoppaMarylandMember / us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis = olp_ConsolidatedJointVentureMember |  |  |
Payments to Acquire Interest in Joint Venture | 5,825,000 us-gaap_PaymentsToAcquireInterestInJointVenture / us-gaap_BusinessAcquisitionAxis = olp_NoxelCorporationIndustrialBuildingJoppaMarylandMember / us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis = olp_ConsolidatedJointVentureMember |  |  |
Regal Cinemas Indianapolis Indiana [Member] |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price | 9,000,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RegalCinemasIndianapolisIndianaMember |  |  |
Third Party Real Estate Acquisition Costs | 78,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RegalCinemasIndianapolisIndianaMember |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 3,087,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_RegalCinemasIndianapolisIndianaMember |  |  |
Building | 5,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_RegalCinemasIndianapolisIndianaMember |  |  |
Building Improvements | 225,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_RegalCinemasIndianapolisIndianaMember |  |  |
Intangible Lease Asset | 1,575,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_RegalCinemasIndianapolisIndianaMember |  |  |
Intangible Lease Liability | (887,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_RegalCinemasIndianapolisIndianaMember |  |  |
Total | 9,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_RegalCinemasIndianapolisIndianaMember |  |  |
Pathmark Supermarket Property Philadelphia Pennsylvania [Member] |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price | 7,729,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember |  |  |
Mortgage incurred | 4,635,000 us-gaap_NoncashOrPartNoncashAcquisitionDebtAssumed1 / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember |  |  |
Third Party Real Estate Acquisition Costs | 162,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember |  |  |
Interest rate (as a percent) | 3.885%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 1,793,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember |  |  |
Building | 5,396,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember |  |  |
Building Improvements | 244,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember |  |  |
Intangible Lease Asset | 440,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember |  |  |
Intangible Lease Liability | (144,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember |  |  |
Total | 7,729,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember |  |  |
Pathmark Supermarket Property Philadelphia Pennsylvania [Member] | Consolidated JV |  |  |  |
Real Estate Acquisitions |  |  |  |
Ownership interest in consolidated joint venture of the company (as a percent) | 90.00%us-gaap_MinorityInterestOwnershipPercentageByParent / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember / us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis = olp_ConsolidatedJointVentureMember |  |  |
Ownership interest in consolidated joint venture of non-controlling interest (as a percent) | 10.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember / us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis = olp_ConsolidatedJointVentureMember |  |  |
Contributions from non-controlling interests | 333,000 us-gaap_NoncontrollingInterestIncreaseFromBusinessCombination / us-gaap_BusinessAcquisitionAxis = olp_PathmarkSupermarketPropertyPhiladelphiaPennsyLvaniaMember / us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis = olp_ConsolidatedJointVentureMember |  |  |
Progress Converting Distribution Facility [Member] |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price | 7,200,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_ProgressConvertingDistributionFacilityMember |  |  |
Third Party Real Estate Acquisition Costs | 38,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_ProgressConvertingDistributionFacilityMember |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land | 881,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_ProgressConvertingDistributionFacilityMember |  |  |
Building | 6,033,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_ProgressConvertingDistributionFacilityMember |  |  |
Building Improvements | 30,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_ProgressConvertingDistributionFacilityMember |  |  |
Intangible Lease Asset | 757,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_ProgressConvertingDistributionFacilityMember |  |  |
Intangible Lease Liability | (501,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_ProgressConvertingDistributionFacilityMember |  |  |
Total | 7,200,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_ProgressConvertingDistributionFacilityMember |  |  |
Other |  |  |  |
Real Estate Acquisitions |  |  |  |
Third Party Real Estate Acquisition Costs | 42,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_OtherPropertiesMember |  |  |
Kmart retail store, Clemmons, North Carolina |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  | 4,640,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyClemmonsNorthCarolinaMember |  |
Third Party Real Estate Acquisition Costs |  | 119,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyClemmonsNorthCarolinaMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land |  | 2,496,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyClemmonsNorthCarolinaMember |  |
Building |  | 2,553,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyClemmonsNorthCarolinaMember |  |
Building Improvements |  | 653,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyClemmonsNorthCarolinaMember |  |
Intangible Lease Asset |  | 425,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyClemmonsNorthCarolinaMember |  |
Intangible Lease Liability |  | (1,487,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyClemmonsNorthCarolinaMember |  |
Total |  | 4,640,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyClemmonsNorthCarolinaMember |  |
Kmart retail store, Clemmons, North Carolina | Consolidated JV |  |  |  |
Real Estate Acquisitions |  |  |  |
Ownership interest in consolidated joint venture of the company (as a percent) |  | 90.00%us-gaap_MinorityInterestOwnershipPercentageByParent / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyClemmonsNorthCarolinaMember / us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis = olp_ConsolidatedJointVentureMember |  |
Ownership interest in consolidated joint venture of non-controlling interest (as a percent) |  | 10.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyClemmonsNorthCarolinaMember / us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis = olp_ConsolidatedJointVentureMember |  |
Contributions from non-controlling interests |  | 470,000 us-gaap_NoncontrollingInterestIncreaseFromBusinessCombination / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyClemmonsNorthCarolinaMember / us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis = olp_ConsolidatedJointVentureMember |  |
Shutterfly flex facility Fort Mill, South Carolina |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  | 15,500,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyFortMillSouthCarolinaMember |  |
Mortgage incurred |  | 9,300,000 us-gaap_NoncashOrPartNoncashAcquisitionDebtAssumed1 / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyFortMillSouthCarolinaMember |  |
Third Party Real Estate Acquisition Costs |  | 124,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyFortMillSouthCarolinaMember |  |
Interest rate (as a percent) |  | 4.562%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyFortMillSouthCarolinaMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land |  | 1,841,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyFortMillSouthCarolinaMember |  |
Building |  | 12,353,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyFortMillSouthCarolinaMember |  |
Building Improvements |  | 335,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyFortMillSouthCarolinaMember |  |
Intangible Lease Asset |  | 1,546,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyFortMillSouthCarolinaMember |  |
Intangible Lease Liability |  | (575,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyFortMillSouthCarolinaMember |  |
Total |  | 15,500,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyFortMillSouthCarolinaMember |  |
Texas Land & Cattle restaurant Killeen, Texas |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  | 2,020,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyKilleenTexasMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land |  | 1,263,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyKilleenTexasMember |  |
Building |  | 739,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyKilleenTexasMember |  |
Building Improvements |  | 64,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyKilleenTexasMember |  |
Total |  | 2,066,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyKilleenTexasMember |  |
Hooters restaurant Concord, North Carolina |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  | 2,469,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyConcordNorthCarolinaMember |  |
Third Party Real Estate Acquisition Costs |  | 15,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyConcordNorthCarolinaMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land |  | 999,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyConcordNorthCarolinaMember |  |
Building |  | 954,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyConcordNorthCarolinaMember |  |
Building Improvements |  | 122,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyConcordNorthCarolinaMember |  |
Intangible Lease Asset |  | 394,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyConcordNorthCarolinaMember |  |
Total |  | 2,469,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyConcordNorthCarolinaMember |  |
TRISUN Health Care - assisted living facility Round Rock, Texas |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  | 22,800,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyRoundRockTexasMember |  |
Mortgage incurred |  | 15,275,000 us-gaap_NoncashOrPartNoncashAcquisitionDebtAssumed1 / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyRoundRockTexasMember |  |
Third Party Real Estate Acquisition Costs |  | 321,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyRoundRockTexasMember |  |
Interest rate (as a percent) |  | 5.375%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyRoundRockTexasMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land |  | 1,678,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyRoundRockTexasMember |  |
Building |  | 16,577,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyRoundRockTexasMember |  |
Building Improvements |  | 93,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyRoundRockTexasMember |  |
Intangible Lease Asset |  | 4,452,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyRoundRockTexasMember |  |
Total |  | 22,800,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyRoundRockTexasMember |  |
Hooters restaurant Myrtle Beach, South Carolina |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  | 2,635,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyMyrtleBeachSouthCarolinaMember |  |
Third Party Real Estate Acquisition Costs |  | 33,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyMyrtleBeachSouthCarolinaMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land |  | 1,102,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyMyrtleBeachSouthCarolinaMember |  |
Building |  | 1,090,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyMyrtleBeachSouthCarolinaMember |  |
Building Improvements |  | 71,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyMyrtleBeachSouthCarolinaMember |  |
Intangible Lease Asset |  | 372,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyMyrtleBeachSouthCarolinaMember |  |
Total |  | 2,635,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyMyrtleBeachSouthCarolinaMember |  |
Joe's Crab Shack restaurant Ann Arbor, Michigan |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  | 2,980,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyAnnArborMichiganMember |  |
Third Party Real Estate Acquisition Costs |  | 31,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyAnnArborMichiganMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land |  | 1,098,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyAnnArborMichiganMember |  |
Building |  | 1,338,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyAnnArborMichiganMember |  |
Building Improvements |  | 122,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyAnnArborMichiganMember |  |
Intangible Lease Asset |  | 422,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyAnnArborMichiganMember |  |
Total |  | 2,980,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyAnnArborMichiganMember |  |
FedEx Express facility Indianapolis, Indiana |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  | 9,270,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyIndianapolisIndianaMember |  |
Third Party Real Estate Acquisition Costs |  | 39,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyIndianapolisIndianaMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land |  | 1,224,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyIndianapolisIndianaMember |  |
Building |  | 6,438,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyIndianapolisIndianaMember |  |
Building Improvements |  | 498,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyIndianapolisIndianaMember |  |
Intangible Lease Asset |  | 1,222,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyIndianapolisIndianaMember |  |
Intangible Lease Liability |  | (112,000)olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleLeaseLiability / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyIndianapolisIndianaMember |  |
Total |  | 9,270,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_RetailPropertyIndianapolisIndianaMember |  |
Northern Tool & Equipment distribution facility Fort Mill, South Carolina |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  | 39,195,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_PropertyLocatedInFortMillSouthCarolinaMember |  |
Mortgage incurred |  | 27,300,000 us-gaap_NoncashOrPartNoncashAcquisitionDebtAssumed1 / us-gaap_BusinessAcquisitionAxis = olp_PropertyLocatedInFortMillSouthCarolinaMember |  |
Third Party Real Estate Acquisition Costs |  | 91,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_PropertyLocatedInFortMillSouthCarolinaMember |  |
Interest rate (as a percent) |  | 4.875%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_BusinessAcquisitionAxis = olp_PropertyLocatedInFortMillSouthCarolinaMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land |  | 1,804,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_PropertyLocatedInFortMillSouthCarolinaMember |  |
Building |  | 31,635,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_PropertyLocatedInFortMillSouthCarolinaMember |  |
Building Improvements |  | 2,014,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_PropertyLocatedInFortMillSouthCarolinaMember |  |
Intangible Lease Asset |  | 3,742,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = olp_PropertyLocatedInFortMillSouthCarolinaMember |  |
Total |  | 39,195,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_PropertyLocatedInFortMillSouthCarolinaMember |  |
Number of tenants in the property | 2 olp_NumberOfTenantsInProperty / us-gaap_BusinessAcquisitionAxis = olp_PropertyLocatedInFortMillSouthCarolinaMember |  |  |
TGIF restaurant, Greensboro, North Carolina |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  | 3,003,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyGreensboroNorthCarolinaMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land |  | 1,768,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyGreensboroNorthCarolinaMember |  |
Building |  | 1,054,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyGreensboroNorthCarolinaMember |  |
Building Improvements |  | 183,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyGreensboroNorthCarolinaMember |  |
Total |  | 3,005,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyGreensboroNorthCarolinaMember |  |
TGIF restaurant, Richmond, Virginia |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  | 3,017,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyRichmondVirginiaMember |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Land |  | 1,678,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLand / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyRichmondVirginiaMember |  |
Building |  | 1,184,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildings / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyRichmondVirginiaMember |  |
Building Improvements |  | 157,000 olp_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedBuildingsImprovements / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyRichmondVirginiaMember |  |
Total |  | 3,019,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertyRichmondVirginiaMember |  |
Other (n) |  |  |  |
Real Estate Acquisitions |  |  |  |
Third Party Real Estate Acquisition Costs |  | 148,000 olp_CostsOfAcquiringRealEstate / us-gaap_BusinessAcquisitionAxis = olp_PriorFiscalYearRealEstateAcquisitionMember |  |
Texas Land & Cattle restaurant Killeen, Texas, TGIF restaurant, Greensboro, North Carolina and TGIF restaurant, Richmond, Virginia |  |  |  |
Allocation of purchase price for the company's real estate acquisitions |  |  |  |
Capitalized transaction costs incurred with the asset acquisition |  | 50,000 us-gaap_BusinessAcquisitionCostOfAcquiredEntityTransactionCosts / us-gaap_BusinessAcquisitionAxis = olp_RestaurantPropertiesKilleenTexasGreensboroNCAndRichmondVAMember |  |
Shopping Center, Lakewood, Colorado | Subsequent event |  |  |  |
Real Estate Acquisitions |  |  |  |
Contract Purchase Price |  |  |  | 17,485,000 us-gaap_PaymentsToAcquireRealEstate / us-gaap_BusinessAcquisitionAxis = olp_ShoppingCenterLakewoodColoradoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Mortgage incurred |  |  |  | $ 11,853,000 us-gaap_NoncashOrPartNoncashAcquisitionDebtAssumed1 / us-gaap_BusinessAcquisitionAxis = olp_ShoppingCenterLakewoodColoradoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Interest rate (as a percent) |  |  |  | 4.12%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_BusinessAcquisitionAxis = olp_ShoppingCenterLakewoodColoradoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Future amortization income of below market leases |  |  |  |
Number of tenant spaces at the property |  |  |  | 29 olp_NumberOfTenantSpacesAtTheProperty / us-gaap_BusinessAcquisitionAxis = olp_ShoppingCenterLakewoodColoradoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Percentage of property leased to tenants |  |  |  | 94.50%olp_AcquiredPropertyPercentageLeased / us-gaap_BusinessAcquisitionAxis = olp_ShoppingCenterLakewoodColoradoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
Ownership percentage in variable interest entity |  |  |  | 90.00%us-gaap_VariableInterestEntityOwnershipPercentage / us-gaap_BusinessAcquisitionAxis = olp_ShoppingCenterLakewoodColoradoMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember

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