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FAIR VALUE MEASUREMENTS (Details) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Fair Value of Financial Instruments |  |  |
Carrying amount | $ 13,250,000 us-gaap_LineOfCredit | $ 23,250,000 us-gaap_LineOfCredit |
Available-for-sale securities: |  |  |
Equity securities | 29,000 us-gaap_AvailableForSaleSecuritiesEquitySecurities |  |
Available-for-sale securities |  |  |
Aggregate cost of available-for-sale securities | 5,300 us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis | 138,000 us-gaap_AvailableForSaleEquitySecuritiesAmortizedCostBasis |
Unrealized gain on available-for-sale securities | 24,000 us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax | 144,000 us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax |
Gross proceeds of available-for-sale securities | 266,000 us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities | 19,000 us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities | 373,000 us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities
Net realized gain on available-for-sale securities | 134,000 us-gaap_AvailableForSaleSecuritiesGrossRealizedGains | 6,000 us-gaap_AvailableForSaleSecuritiesGrossRealizedGains | 9,000 us-gaap_AvailableForSaleSecuritiesGrossRealizedGains
Gain on sale shares sold to related party | 134,000 us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet | 6,000 us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet | 9,000 us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet
Facility |  |  |
Fair Value of Financial Instruments |  |  |
Carrying amount | 13,250,000 us-gaap_LineOfCredit / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember | 23,250,000 us-gaap_LineOfCredit / us-gaap_CreditFacilityAxis = us-gaap_RevolvingCreditFacilityMember |
Carrying and fair Value |  |  |
Available-for-sale securities: |  |  |
Equity securities | 29,000 us-gaap_AvailableForSaleSecuritiesEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | 282,000 us-gaap_AvailableForSaleSecuritiesEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Carrying and fair Value | Interest rate swap |  |  |
Available-for-sale securities: |  |  |
Derivative financial instruments | 27,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | 265,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Financial liabilities: |  |  |
Derivative financial instruments | 3,139,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember | 774,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_CarryingReportedAmountFairValueDisclosureMember |
Level 1 |  |  |
Available-for-sale securities: |  |  |
Equity securities | 29,000 us-gaap_AvailableForSaleSecuritiesEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 282,000 us-gaap_AvailableForSaleSecuritiesEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member |
Level 2 | Interest rate swap |  |  |
Available-for-sale securities: |  |  |
Derivative financial instruments | 27,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 265,000 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
Financial liabilities: |  |  |
Derivative financial instruments | 3,139,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 774,000 us-gaap_DerivativeFairValueOfDerivativeLiability / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_InterestRateSwapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
BRT Realty Trust |  |  |
Available-for-sale securities: |  |  |
Equity securities |  | 262,000 us-gaap_AvailableForSaleSecuritiesEquitySecurities / us-gaap_InvestmentTypeAxis = olp_BRTRealtyTrustSecuritiesMember |
Available-for-sale securities |  |  |
Investment in available-for-sale equity securities (in shares) |  | 37,081 us-gaap_InvestmentOwnedBalanceShares / us-gaap_InvestmentTypeAxis = olp_BRTRealtyTrustSecuritiesMember |
BRT Realty Trust | Gould |  |  |
Available-for-sale securities |  |  |
Gross proceeds of available-for-sale securities | 266,000 us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities / us-gaap_InvestmentTypeAxis = olp_BRTRealtyTrustSecuritiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = olp_GouldInvestorsLPMember |  |
Number of shares sold to related party | 37,081 olp_RelatedPartyTransactionNumberOfSharesSold / us-gaap_InvestmentTypeAxis = olp_BRTRealtyTrustSecuritiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = olp_GouldInvestorsLPMember |  |
Period based on which average of the closing prices considered for proceeds from related party | 30 days |  |
Cost of shares sold to related party | 132,000 us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = olp_BRTRealtyTrustSecuritiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = olp_GouldInvestorsLPMember |  |
Gain on sale shares sold to related party | 134,000 us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet / us-gaap_InvestmentTypeAxis = olp_BRTRealtyTrustSecuritiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = olp_GouldInvestorsLPMember |  |
Gain reclassified from accumulated other comprehensive loss on the balance sheet into earnings | 132,000 us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax / us-gaap_InvestmentTypeAxis = olp_BRTRealtyTrustSecuritiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = olp_GouldInvestorsLPMember |  |
Other equity securities |  |  |
Available-for-sale securities: |  |  |
Equity securities |  | 20,000 us-gaap_AvailableForSaleSecuritiesEquitySecurities / us-gaap_InvestmentTypeAxis = olp_OtherEquitySecuritiesMember |
Mortgages payable |  |  |
Fair Value of Financial Instruments |  |  |
Estimated fair value of mortgages payable | 300,541,000 us-gaap_DebtInstrumentFairValue / us-gaap_LongtermDebtTypeAxis = us-gaap_MortgagesMember | 283,142,000 us-gaap_DebtInstrumentFairValue / us-gaap_LongtermDebtTypeAxis = us-gaap_MortgagesMember |
Excess of fair value over carrying value | $ 8,492,000 olp_DebtInstrumentExcessOfEstimatedFairValueOverCarryingValue / us-gaap_LongtermDebtTypeAxis = us-gaap_MortgagesMember | $ 5,097,000 olp_DebtInstrumentExcessOfEstimatedFairValueOverCarryingValue / us-gaap_LongtermDebtTypeAxis = us-gaap_MortgagesMember |
Blended or estimated market interest rate (as a percent) | 4.50%us-gaap_FairValueInputsDiscountRate / us-gaap_LongtermDebtTypeAxis = us-gaap_MortgagesMember | 5.00%us-gaap_FairValueInputsDiscountRate / us-gaap_LongtermDebtTypeAxis = us-gaap_MortgagesMember |
Weighted average remaining term of the mortgages |  | 9 years |
Mortgages and loan payable |  |  |
Fair Value of Financial Instruments |  |  |
Weighted average remaining term of the mortgages | 9 years 1 month 6 days |  |

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- Definition This item represents the cost of equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments for other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
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- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
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- Definition Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20, 22 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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