Number of Management Agreements

No definition available.

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Namespace Prefix:	dhc_
Data Type:	xbrli:integerItemType
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- Definition

Represents the number of persons employed by a related party of the entity.

+ References

No definition available.

+ Details

Name:	dhc_RelatedPartyEmployeesNumber
Namespace Prefix:	dhc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Related Party Transaction, Business Management Agreement Annual Incentive Fee Estimate Included in Management Fees

+ References

No definition available.

+ Details

Name:	dhc_RelatedPartyTransactionBusinessManagementAgreementAnnualIncentiveFeeEstimateIncludedinManagementFees
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the business management fees incurred pursuant to business management agreement with related parties.

+ References

No definition available.

+ Details

Name:	dhc_RelatedPartyTransactionBusinessManagementFees
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Related Party Transaction Business Management Fees Related to Subsidiary Level Management

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No definition available.

+ Details

Name:	dhc_RelatedPartyTransactionBusinessManagementFeesRelatedtoSubsidiaryLevelManagement
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Related Party Transaction, Period Of Actual Amount Of Incentive Fees

+ References

No definition available.

+ Details

Name:	dhc_RelatedPartyTransactionPeriodOfActualAmountOfIncentiveFees
Namespace Prefix:	dhc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the property management and construction supervision fees incurred pursuant to business and property management agreements with related parties.

+ References

No definition available.

+ Details

Name:	dhc_RelatedPartyTransactionPropertyManagementAndConstructionSupervisionFees
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the property management and construction supervision fees paid to related parties.

+ References

No definition available.

+ Details

Name:	dhc_RelatedPartyTransactionPropertyManagementAndConstructionSupervisionFeesPaid
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=dhc_SeniorLivingCommunityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
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Balance Type:
Period Type:

- Details

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Business and Property Management Agreements with RMR LLC (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) employee management_agreement	Mar. 31, 2019 USD ($)	Dec. 31, 2020
Related person transactions
Number of employees \| employee	0
Property management and construction supervision fees	$ 3,192,000	$ 3,064,000
Property management and construction supervision fees paid	3,443,000	3,374,000
RMR LLC
Related person transactions
Business management fees incurred	5,769,000	7,719,000
Related party transaction business management fees related to subsidiary level management	725,000
Related party transaction business management agreement, annual incentive fee estimate included in management fees	$ 0	$ 0
Senior Living Communities \| RMR Inc
Related person transactions
Number of management agreements \| management_agreement	2
Subsequent Event \| Scenario, Forecast \| RMR LLC
Related person transactions
Period of actual amount of incentive fees			3 years