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

No definition available.

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

- Definition

Represents the number of employees in the company.

+ References

No definition available.

+ Details

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

- Definition

Total expense amount to reimburse a related party.

+ References

No definition available.

+ Details

Name:	opi_RelatedPartyReimbursementExpense
Namespace Prefix:	opi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of expense for incentive rights held by the managing member or general partner, of limited liability company (LLC) or limited partnership (LP).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

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

- Definition

Amount of transactions with related party during the financial reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864

+ Details

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

- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

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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

- Details

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Balance Type:
Period Type:

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=opi_BuildingsAndImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_OtherOperatingIncomeExpenseMember
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Business and Property Management Agreements with RMR LLC (Details) - RMR LLC $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) employee agreement	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Related Party Transaction [Line Items]
Number of employees \| employee			0
Number of agreements \| agreement			2
Incentive fee (reversal)	$ (6,627)	$ 0	$ 4,484	$ 0	$ 0
Reimbursement expense	6,131	6,437	18,108	18,687
Net Property Management and Construction Supervision Fees
Related Party Transaction [Line Items]
Related party expense	(1,738)	4,236	18,287	13,237
Related party transaction amount	5,519	5,189	15,045	15,381
Net Property Management and Construction Supervision Fees \| Buildings and Improvements
Related Party Transaction [Line Items]
Related party transaction amount	1,295	887	2,806	2,429
Net Property Management and Construction Supervision Fees \| Other Operating Income (Expense)
Related Party Transaction [Line Items]
Related party transaction amount	$ 4,224	$ 4,302	$ 12,239	$ 12,952