CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 22,210,000us-gaap_ProfitLoss	$ 17,924,000us-gaap_ProfitLoss	$ 32,308,000us-gaap_ProfitLoss
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on disposition of real estate held by unconsolidated joint venture		(2,807,000)
Gain on sale - unconsolidated joint venture interest		(1,898,000)
Gain on sale of available-for-sale securities (to related party in 2014)	(134,000)	(6,000)	(9,000)
Gain on sales of real estate	(10,180,000)		(19,732,000)
Impairment loss/charge	1,093,000	62,000
Prepayment costs on debt related to sale of real estate	1,581,000
Increase in rental income from straight-lining of rent	(1,490,000)us-gaap_StraightLineRent	(1,114,000)us-gaap_StraightLineRent	(1,354,000)us-gaap_StraightLineRent
Increase in rental income resulting from bad debt recovery, net			(117,000)us-gaap_ProvisionForLoanAndLeaseLosses
(Increase) decrease in rental income from amortization of intangibles relating to leases	(267,000)	(160,000)	2,000
Amortization of restricted stock expense	1,833,000us-gaap_ShareBasedCompensation	1,440,000us-gaap_ShareBasedCompensation	1,223,000us-gaap_ShareBasedCompensation
Equity in earnings of unconsolidated joint ventures	(533,000)	(651,000)	(1,368,000)
Distributions of earnings from unconsolidated joint ventures	502,000	1,103,000	1,016,000
Depreciation and amortization	14,662,000	12,043,000	9,966,000
Amortization and write off of financing costs	1,037,000us-gaap_AmortizationOfFinancingCosts	891,000us-gaap_AmortizationOfFinancingCosts	800,000us-gaap_AmortizationOfFinancingCosts
Payment of leasing commissions	(165,000)us-gaap_PaymentsForLeaseCommissions	(200,000)us-gaap_PaymentsForLeaseCommissions	(438,000)us-gaap_PaymentsForLeaseCommissions
Decrease (Increase) in escrow, deposits, other assets and receivables	1,149,000	(1,653,000)	(492,000)
Increase in accrued expenses and other liabilities	505,000	1,763,000	71,000
Net cash provided by operating activities	31,803,000	26,737,000	21,876,000
Cash flows from investing activities:
Purchase of real estate	(57,096,000)	(107,579,000)	(44,088,000)
Improvements to real estate	(769,000)	(2,867,000)	(4,969,000)
Net proceeds from sale of real estate	43,788,000		36,062,000
Net proceeds from disposition of unconsolidated joint venture interest		13,444,000
Distributions of return of capital from unconsolidated joint ventures	53,000	5,495,000	145,000
Net proceeds from sale of available-for-sale securities(to related party in 2014)	266,000	19,000	373,000
Net cash used in investing activities	(13,758,000)	(91,488,000)	(12,477,000)
Cash flows from financing activities:
Scheduled amortization payments of mortgages payable	(7,597,000)	(6,808,000)	(5,533,000)
Repayment of mortgages payable	(38,873,000)us-gaap_RepaymentsOfSecuredDebt	(4,708,000)us-gaap_RepaymentsOfSecuredDebt	(32,422,000)us-gaap_RepaymentsOfSecuredDebt
Prepayment costs on debt related to sale of real estate	(1,581,000)olp_PrepaymentCostsOnDebtRelatedToSale
Proceeds from mortgage financings	60,474,000	63,590,000	65,989,000
Proceeds from common stock offering, net	3,768,000	9,165,000	2,131,000
Proceeds from bank line of credit	42,500,000	32,500,000	14,550,000
Repayment on bank line of credit	(52,500,000)	(9,250,000)	(34,550,000)
Issuance of shares through dividend reinvestment plan	4,449,000	4,235,000	3,652,000
Payment of financing costs	(1,782,000)us-gaap_PaymentsOfFinancingCosts	(656,000)us-gaap_PaymentsOfFinancingCosts	(2,111,000)us-gaap_PaymentsOfFinancingCosts
Capital contributions from non-controlling interests	639,000	480,000	571,000
Distributions to non-controlling interests	(228,000)us-gaap_PaymentsToMinorityShareholders	(298,000)us-gaap_PaymentsToMinorityShareholders	(290,000)us-gaap_PaymentsToMinorityShareholders
Cash distributions to common stockholders	(23,601,000)us-gaap_PaymentsOfDividendsCommonStock	(21,445,000)us-gaap_PaymentsOfDividendsCommonStock	(19,477,000)us-gaap_PaymentsOfDividendsCommonStock
Net cash (used in) provided by financing activities	(14,332,000)	66,805,000	(7,490,000)
Net increase in cash and cash equivalents	3,713,000	2,054,000	1,909,000
Cash and cash equivalents at beginning of year	16,631,000	14,577,000	12,668,000
Cash and cash equivalents at end of year	20,344,000	16,631,000	14,577,000
Supplemental disclosures of cash flow information:
Cash paid during the year for interest expense, net of capitalized interest of $9 and $35 in 2013 and 2012, respectively	16,403,000us-gaap_InterestPaid	13,744,000us-gaap_InterestPaid	13,088,000us-gaap_InterestPaid
Cash paid during the year for income taxes	90,000us-gaap_IncomeTaxesPaid	78,000us-gaap_IncomeTaxesPaid	68,000us-gaap_IncomeTaxesPaid
Cash paid during the year for Federal excise tax	64,000olp_FederalExciseTaxPaid	290,000olp_FederalExciseTaxPaid
Supplemental schedule of non-cash investing and financing activities:
Contribution of property to unconsolidated joint venture			11,734,000us-gaap_ContributionOfProperty
Purchase accounting allocations - intangible lease assets	4,771,000	11,624,000	6,641,000
Purchase accounting allocations - intangible lease liabilities	(4,376,000)	(2,210,000)	(588,000)
Restricted cash received for tenant improvements and other reserve, net	$ 1,607,000

Cash flow impact of gain (loss) after tax expense or benefit, not previously recognized and resulting from the sale of a business component, which is recognized at the date of sale. A gain (loss) reflects the amount by which the consideration received exceeds (is exceeded by) the net carrying amount (reflecting previous provisions for loss on disposal, if any) of the disposal group.

No definition available.