Represents the number of agreements with RMR LLC to provide management services to the company.

No definition available.

Name:	opi_NumberOfAgreementsWithRmrLlc
Namespace Prefix:	opi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the aggregate cost of investments accounted for under the equity method of accounting.

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Balance Type:	debit
Period Type:	instant

- Definition

Amount of income (loss) for proportionate share of equity method investee's income (loss).

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Balance Type:	credit
Period Type:	duration

- Definition

Amount of distribution received from equity method investee for return of investment, classified as investing activities. Excludes distribution for return on investment, classified as operating activities.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=opi_AffiliatesInsuranceCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Related Person Transactions (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
Related Person Transactions (Details) $ in Thousands	Jun. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) agreement	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Related Party Transaction [Line Items]
Equity in earnings of an investee		$ (279)	$ (196)	$ (815)	$ (573)
RMR LLC
Related Party Transaction [Line Items]
Number of agreements \| agreement				2
Revenue from related party		282	288	$ 836	854
AIC
Related Party Transaction [Line Items]
Carrying value of equity method investments		11		11		$ 298
Distributions in excess of earnings from unconsolidated joint ventures	$ 287
Equity in earnings of an investee		$ 0	$ 83	$ 0	$ 617