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

No definition available.

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

- Definition

Represents the number of communities managed by a related party.

+ References

No definition available.

+ Details

Name:	dhc_NumberOfCommunitiesManagedByRelatedParty
Namespace Prefix:	dhc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Communities Leased by the Company

+ References

No definition available.

+ Details

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

- Definition

Related Party Transaction, Amount Of Improvements To Communities To Leased Asset

+ References

No definition available.

+ Details

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

- Definition

Related Party Transaction, Business And Property Management Agreement, Number of Agreements

+ References

No definition available.

+ Details

Name:	dhc_RelatedPartyTransactionBusinessAndPropertyManagementAgreementNumberofAgreements
Namespace Prefix:	dhc_
Data Type:	xbrli:integerItemType
Balance Type:	na
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, Monthly Minimum Rent Payable

+ References

No definition available.

+ Details

Name:	dhc_RelatedPartyTransactionMonthlyMinimumRentPayable
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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 Transaction, Percentage Target EBITDA Of New Management Agreement Not Earned For All Communities

+ References

No definition available.

+ Details

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

- Definition

Related Party Transaction, Percentage of Annual Incentive Fee

+ References

No definition available.

+ Details

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

- Definition

Represents the management fees payable to related parties under property management agreement expressed as a percentage of gross revenues.

+ References

No definition available.

+ Details

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

- Definition

Related Party Transaction, Property Management Agreement, Management Fees as Percentage of Gross Revenues Realized At All Communities

+ References

No definition available.

+ Details

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

- Definition

Related Party Transaction, Property Management Agreement, Renewal Term

+ References

No definition available.

+ Details

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

- Definition

Represents the annual rent as a percentage of the entity's gross revenues.

+ References

No definition available.

+ Details

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

- Definition

Related Party Transaction, Transaction Agreement Annual Rent as a Percentage of Gross Revenues, Amount

+ References

No definition available.

+ Details

Name:	dhc_RelatedPartyTransactionTransactionAgreementAnnualRentasaPercentageofGrossRevenuesAmount
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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=6877327&loc=d3e13212-122682

+ Details

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

- 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
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13537-108611

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

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

- 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=77888415&loc=SL77918607-209975

+ Details

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

- Definition

The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3213-108585

+ Details

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

- Definition

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

+ 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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39622-107864

Reference 3: 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

+ Details

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

- Details

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

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

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=dhc_ShareholdersMember
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:	srt_ProductOrServiceAxis=dhc_RentalIncomeMember
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:	us-gaap_ConcentrationRiskByBenchmarkAxis=dhc_RealEstateInvestmentPropertyAtCostMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=dhc_RentalPropertyConcentrationMember
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		3 Months Ended		12 Months Ended
	Apr. 01, 2019 USD ($)	Mar. 31, 2020 USD ($) renewal_option community shares	Mar. 31, 2019 USD ($) community	Dec. 31, 2019 community shares	Jan. 01, 2020 shares	Feb. 01, 2019 USD ($)
Common shares of beneficial interest, shares issued (in shares) \| shares		237,893,725		237,897,163
Gain on lease termination		$ 22,896	$ 0
Senior Living Communities
Payments to acquire assets	$ 49,155
Five Star
Total rental income recognized		$ 75,000
Monthly minimum rent payable						$ 11,000
Management fees as percentage of gross revenues		5.00%
Percentage of annual incentive fee		15.00%
Percentage of gross revenues realized at all communities		1.50%
Number of consecutive renewal terms of agreement \| renewal_option		2
Related Party Transaction, Property Management Agreement, Renewal Term		5 years
Percentage target EBITDA of new management agreement not earned		90.00%
Percentage target EBITDA of new management agreement not earned for all communities		20.00%
Amount of improvements to communities			22,579
Five Star
Annual rent plus percentage		4.00%
Annual rent as a percentage			$ 538
Five Star \| Senior Living Communities
Number of communities managed by related party \| community		244	76
Five Star
Common shares of beneficial interest, shares issued (in shares) \| shares					10,268,158
Five Star \| Shareholders
Common shares of beneficial interest, shares issued (in shares) \| shares					16,118,849
Five Star
Number of communities leased by the company \| community				166
Number of communities managed by related party \| community				78
Total rental income recognized			$ 39,313
Investment owned, percentage of total shares outstanding		33.90%
Property management agreement expense		$ 16,588	$ 3,789
Five Star \| Rental income \| Rents from significant lessee \| Investment
Percentage of rental income			14.80%
Five Star \| Rental Property Concentration \| Rents from significant lessee \| Investment
Percentage of rental income			26.50%
Five Star \| Rehabilitation Services
Expenses from transactions with related party		$ 8,057	$ 1,675