Number of shares was purchased in open market during the period.

No definition available.

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- Definition

Represents the amount of annual fixed rent required to be paid by the entity.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the additional amount of consideration authorized under the compensation and services agreement with the related party.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of additional payment to related party for the share of direct office expenses.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount agreed to be paid to related parties under related party transaction.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount authorized under compensation and service agreement with the related party.

+ References

No definition available.

+ Details

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Namespace Prefix:	olp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Represents the amount of annual fee paid in consideration for providing services.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of ownership held by the related party.

+ References

No definition available.

+ Details

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Namespace Prefix:	olp_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the amount of property management costs allocated to real estate expenses annually.

+ References

No definition available.

+ Details

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

- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Paragraph A240

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-Paragraph 64

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 14.F)

-URI http://asc.fasb.org/extlink&oid=6793087&loc=d3e301413-122809

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Balance Type:	debit
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- Definition

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

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-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 12

-Paragraph 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 30

-Article 5

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-Name Regulation S-X (SX)

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-Section 04

-Article 3

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-Topic 505

-SubTopic 10

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-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

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- Details

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Balance Type:	na
Period Type:	duration

- Definition

Number of shares issued during the period from a dividend reinvestment plan (DRIP). A dividend reinvestment plan allows the shareholders to reinvest dividends paid to them by the entity on new issues of stock by the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

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RELATED PARTY TRANSACTIONS (Details) (USD $)	0 Months Ended		12 Months Ended
RELATED PARTY TRANSACTIONS (Details) (USD $)	Sep. 13, 2011	Jan. 02, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
RELATED PARTY TRANSACTIONS
Number of shares of common stock owned by the related party			14,598,000	14,213,000
Number of shares purchased by the related party under the dividend reinvestment plan			214,620	254,502	81,154
Cost of plans charged to operations			$ 1,223,000	$ 1,009,000	$ 915,000
Annual lease rent			296,875
Gould
RELATED PARTY TRANSACTIONS
Number of shares of common stock owned by the related party			1,524,009	1,450,670
Ownership percentage held by the related party			10.20%	10.00%
Number of shares purchased by the related party in the open market			301
Number of shares purchased by the related party under the dividend reinvestment plan			73,038	104,395
Majestic
RELATED PARTY TRANSACTIONS
Annual fee paid in consideration for providing services			2,725,000	2,725,000	2,225,000
Property management costs allocated to real estate expenses annually			600,000
Additional payment for the entity's share of all direct office expenses			175,000	175,000	175,000
Increase in amount authorized under compensation and services agreement	500,000
Amount authorized under compensation and service agreement		2,400,000	2,900,000
Chairman
RELATED PARTY TRANSACTIONS
Amount agreed to be paid			250,000
Vice Chairman
RELATED PARTY TRANSACTIONS
Amount agreed to be paid			100,000
Subsidiary of Gould
RELATED PARTY TRANSACTIONS
Annual lease rent			41,000	47,000	45,000
Executive officers and others
RELATED PARTY TRANSACTIONS
Cost of plans charged to operations			$ 743,000	$ 603,000	$ 553,000