Lease Termination Fee Income (Details) - USD ($)	1 Months Ended	6 Months Ended
Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015
Lease Termination Fee Income
Lease termination fee received from a retail tenant in a lease buy-out transaction	$ 650,000	$ 1,269,000
Write-off of entire balance of the unbilled rent receivable and the intangible lease asset		$ 150,000
Write-off of entire balance of the unbilled rent receivable	$ 226,000		$ 226,000

Write-off of Unbilled Rent Receivable and Intangible Lease Asset

No definition available.

Name:	olp_WriteoffOfUnbilledRentReceivableAndIntangibleLeaseAsset
Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration