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Commitments (Details) | Sep. 30, 2018 USD ($)
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Building Located In Hauppauge New York |
Commitments |
Contractual obligation | $ 960,000

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- Definition Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=olp_BuildingLocatedInHauppaugeNewYorkMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |