Represents the number of other governments that are tenants of the entity.

No definition available.

Name:	opi_NumberOfOtherGovernments
Namespace Prefix:	opi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number Of Properties

+ References

No definition available.

+ Details

Name:	opi_NumberOfProperties
Namespace Prefix:	opi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of state governments that are tenants of the entity.

+ References

No definition available.

+ Details

Name:	opi_NumberOfStateGovernments
Namespace Prefix:	opi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of states in which real estate owned by the entity is located as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	opi_NumberOfStatesInWhichRealEstatePropertiesHeld
Namespace Prefix:	opi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the percentage of rental income in each state.

+ References

No definition available.

+ Details

Name:	opi_RealEstateRevenuePercent
Namespace Prefix:	opi_
Data Type:	num:percentItemType
Balance Type:	na
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

Name:	us-gaap_ConcentrationRiskLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementOperatingActivitiesSegmentAxis=us-gaap_SegmentContinuingOperationsMember
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- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=opi_RealEstateRevenueNetMember
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- Details

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- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

Name:	srt_MajorCustomersAxis=opi_USGovernmentMember
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Concentration (Details)	12 Months Ended
Concentration (Details)	Dec. 31, 2019 property state government_tenant state_government	Dec. 31, 2018 government	Dec. 31, 2017 government_tenant
Continuing Operations
Concentration Risk [Line Items]
Number of properties \| property	189
Number of states in which acquired properties located \| state	35
Annualized Rental Income, Excluding Properties Classified as Discontinued Operations \| Virginia
Concentration Risk [Line Items]
Annualized rental income percent	15.60%
Annualized Rental Income, Excluding Properties Classified as Discontinued Operations \| California
Concentration Risk [Line Items]
Annualized rental income percent	11.90%
Annualized Rental Income, Excluding Properties Classified as Discontinued Operations \| District of Columbia
Concentration Risk [Line Items]
Concentration risk, percentage	24.10%
Annualized rental income percent	10.40%
Annualized Rental Income, Excluding Properties Classified as Discontinued Operations \| Texas
Concentration Risk [Line Items]
Annualized rental income percent	7.90%
Annualized Rental Income, Excluding Properties Classified as Discontinued Operations \| Maryland
Concentration Risk [Line Items]
Annualized rental income percent	6.60%
Annualized Rental Income, Excluding Properties Classified as Discontinued Operations \| Tenant Concentration \| U S Government, State Governments, and Other Governments
Concentration Risk [Line Items]
Number of state governments	11	13
Number of other governments \| government_tenant	2		3
Concentration risk, percentage	35.50%	35.40%	62.60%
Annualized Rental Income, Excluding Properties Classified as Discontinued Operations \| Tenant Concentration \| U.S. Government
Concentration Risk [Line Items]
Concentration risk, percentage	25.00%	25.60%	43.50%