Leases - Narrative (Details) $ in Thousands	12 Months Ended
Dec. 31, 2024 USD ($) tenant	Dec. 31, 2023 USD ($)
Lessee, Lease, Description [Line Items]
Straight line rent adjustments	$ 31,102	$ 26,194
Straight line rent receivables	140,132	112,440
Variable lease, income	86,903	88,173
Tenant reimbursement income	$ 82,647	$ 82,885
Lessor, Operating Lease, Payment to be Received
Lessee, Lease, Description [Line Items]
Number of government tenants with the right to terminate their leases \| tenant	5
Lessor, Operating Lease, Payment to be Received \| Tenant with Exercisable Termination Rights \| Tenant Concentration
Lessee, Lease, Description [Line Items]
Concentration risk, percentage	1.20%
2025	1.40%
2026	1.90%
2027	2.00%
2028	5.70%
2029	4.10%
2030	2.60%
2031	1.80%
2032	5.70%
2034	1.50%
2035	4.40%
2036	0.60%
2037	0.60%
2040	2.30%
Lessor, Operating Lease, Payment to be Received \| Fourteen Government Tenants \| Tenant Concentration
Lessee, Lease, Description [Line Items]
Concentration risk, percentage	2.80%

Concentration Risk Percentage for Termination Right Exercisable in Year Eleven

No definition available.

Name:	opi_ConcentrationRiskPercentageForTerminationRightExercisableInYearEleven
Namespace Prefix:	opi_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage as a concentration risk for termination right exercisable in year five from the balance sheet date.

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageForTerminationRightExercisableInYearFive
Namespace Prefix:	opi_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage as a concentration risk for termination right exercisable in year four from the balance sheet date.

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageForTerminationRightExercisableInYearFour
Namespace Prefix:	opi_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage as a concentration risk for termination right exercisable in year six from the balance sheet date.

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageForTerminationRightExercisableInYearSix
Namespace Prefix:	opi_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Concentration Risk Percentage for Termination Right Exercisable in Year Sixteen

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageForTerminationRightExercisableInYearSixteen
Namespace Prefix:	opi_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Concentration Risk Percentage for Termination Right Exercisable in Year Ten

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageForTerminationRightExercisableInYearTen
Namespace Prefix:	opi_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Concentration Risk Percentage for Termination Right Exercisable in Year Thirteen

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageForTerminationRightExercisableInYearThirteen
Namespace Prefix:	opi_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage as a concentration risk for termination right exercisable in year three from the balance sheet date.

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageForTerminationRightExercisableInYearThree
Namespace Prefix:	opi_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Concentration Risk Percentage for Termination Right Exercisable in Year Twelve

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageForTerminationRightExercisableInYearTwelve
Namespace Prefix:	opi_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage as a concentration risk for termination right exercisable in year two from the balance sheet date.

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageForTerminationRightExercisableInYearTwo
Namespace Prefix:	opi_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Concentration Risk Percentage for Termination Right, Exercisable Next Twelve Months

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageforTerminationRightExercisableNextTwelveMonths
Namespace Prefix:	opi_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Concentration Risk Percentage for Termination Right Exercisable in Year Eight

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageforTerminationRightExercisableinYearEight
Namespace Prefix:	opi_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Concentration Risk Percentage for Termination Right, Exercisable in Year Seven

+ References

No definition available.

+ Details

Name:	opi_ConcentrationRiskPercentageforTerminationRightExercisableinYearSeven
Namespace Prefix:	opi_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Lessee, Operating Lease, Number Of Government Tenants With The Right To Terminate Their Leases

+ References

No definition available.

+ Details

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

- Definition

Tenant Reimbursement Income

+ References

No definition available.

+ Details

Name:	opi_TenantReimbursementIncome
Namespace Prefix:	opi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-42

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-21

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-20

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-18

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-20

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of excess of rental income recognized over rental payment required by lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 840
-SubTopic 20
-Name Accounting Standards Codification
-Section 35
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481123/840-20-35-2

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 840
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481178/840-20-25-1

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 25
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479341/842-30-25-11

Reference 4: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 840
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481178/840-20-25-2

+ Details

Name:	us-gaap_DeferredRentReceivablesNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7A
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-7A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

+ Details

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

- Definition

Amount of the adjustment to rental revenues to measure escalating leasing revenues on a straight line basis.

+ References

No definition available.

+ Details

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

- Definition

Amount of variable lease payments from operating, direct financing, and sales-type leases, excluding amount included in measurement of lease receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479773/842-30-50-5

+ Details

Name:	us-gaap_VariableLeaseIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=opi_LessorOperatingLeasePaymentToBeReceivedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MajorCustomersAxis=opi_TenantWithExercisableTerminationRightsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MajorCustomersAxis=opi_FourteenGovernmentTenantsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: