SCHEDULE III REAL ESTATE AND ACCUMULATED DEPRECIATION [Schedule] - Additional Information (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($)
SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Abstract]
Mortgage debt, net	$ 3,135
Aggregate cost for federal income tax purposes	$ 6,971,434
Useful life of buildings and improvements	40 years
Useful life of equipment	12 years

Represents the estimated economic life of buildings and improvements on which depreciation in the latest income statement was computed.

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Represents the estimated economic life of equipment on which depreciation in the latest income statement was computed.

+ References

No definition available.

+ Details

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Namespace Prefix:	opi_
Data Type:	xbrli:durationItemType
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- References

No definition available.

+ Details

Name:	srt_RealEstateAndAccumulatedDepreciationDisclosureAbstract
Namespace Prefix:	srt_
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- Definition

Cost basis of real estate investments for federal income tax purposes for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Footnote 6
-Subsection 28

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 970
-SubTopic 360
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-28(Footnote 6))
-URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024

+ Details

Name:	srt_RealEstateFederalIncomeTaxBasis
Namespace Prefix:	srt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column G))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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