Aggregate Shares Issued

No definition available.

Name:	dhc_AggregateSharesIssued
Namespace Prefix:	dhc_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of shares held as a percentage of the total shares outstanding at the end of the period.

+ References

No definition available.

+ Details

Name:	dhc_InvestmentOwnedPercentageOfTotalSharesOutstanding
Namespace Prefix:	dhc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Real Estate Properties Inadequate Documentation

+ References

No definition available.

+ Details

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

- Definition

Payments Made In Exchange For Customary Release

+ References

No definition available.

+ Details

Name:	dhc_PaymentsMadeInExchangeForCustomaryRelease
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Related Party Transaction Capitalized Amount

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Related Party Transaction, Percentage Target EBITDA Of New Management Agreement Not Earned

+ References

No definition available.

+ Details

Name:	dhc_RelatedPartyTransactionPercentageTargetEBITDAOfNewManagementAgreementNotEarned
Namespace Prefix:	dhc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Related Party Transactions, Termination Percentage

+ References

No definition available.

+ Details

Name:	dhc_RelatedPartyTransactionsTerminationPercentage
Namespace Prefix:	dhc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Revenue Reserve, Management Fees Payable Reduction

+ References

No definition available.

+ Details

Name:	dhc_RevenueReserveManagementFeesPayableReduction
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_CommonStockSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of gain (loss) on termination of lease before expiration of lease term.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 40
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121604053&loc=SL77918607-209975

+ Details

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

- Definition

Amount of lease income from operating, direct financing, and sales-type leases. Includes, but is not limited to, variable lease payments, interest income, profit (loss) recognized at commencement, and lease payments paid and payable to lessor.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121576215&loc=SL77919372-209981

+ Details

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

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfRealEstateProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of units in a real estate property owned as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfUnitsInRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- 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

Name:	us-gaap_RelatedPartyTransactionAmountsOfTransaction
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

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

- Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=dhc_FiveStarQualityCareIncMember
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_DisposalGroupClassificationAxis=us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=dhc_FiveStarQualityCareIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_OperatingExpenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupDisposedOfByMeansOtherThanSaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=dhc_RehabilitationServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Leases and Management Agreements with Five Star - Narrative (Details) $ in Thousands		1 Months Ended	3 Months Ended
	Apr. 09, 2021 USD ($) unit community	Jan. 31, 2021 USD ($)	Mar. 31, 2021 USD ($) community property trustee shares	Mar. 31, 2020 USD ($) community	Dec. 31, 2020 shares	Dec. 31, 2019 shares
Common shares of beneficial interest, shares issued (in shares) \| shares			238,268,478		238,268,478
Gain on lease termination			$ 0	$ 22,896
Number of properties (property) \| property			396
Rental income			$ 397	294
Five Star
Total rental income recognized				75,000
Gain on lease termination				$ 22,896
Five Star
Payments made in exchange for customary release		$ 5,763
Five Star \| Senior Living Communities
Number of properties (property) \| community			235	244
Number of real estate properties inadequate documentation \| trustee			1
Revenue reserve, management fees payable reduction			$ 115
Five Star \| Senior Living Communities \| Closed
Number of properties (property) \| community			7
Five Star
Common shares of beneficial interest, shares issued (in shares) \| shares						10,268,158
Aggregate Shares Issued \| shares					16,118,849
Five Star
Investment owned, percentage of total shares outstanding			33.80%
Property management agreement expense			$ 13,850	$ 17,050
Related party transaction capitalized amount			834	462
Five Star \| Operating Expense
Property management agreement expense			13,016	16,588
Five Star \| Senior Living Communities \| Subsequent Event
Number of properties (property) \| community	120
Number of property units (units) \| unit	18,000
Related party transactions, termination percentage	10.00%
Percentage target EBITDA of new management agreement not earned	80.00%
Five Star \| Senior Living Communities \| Subsequent Event \| Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations
Total rental income recognized	$ 682,000
Number of properties (property) \| community	108
Number of property units (units) \| unit	7,500
Five Star \| Senior Living Communities \| Subsequent Event \| Closed
Number of property units (units) \| unit	1,500
Five Star \| Rehabilitation Services
Expenses from transactions with related party			$ 5,441	$ 8,057