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

Represents the number of management agreements RMR LLC would need to terminate for good cause before a termination fee is incurred.

No definition available.

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

Represents the number of management agreements the company would need to terminate for a performance reason before a termination fee is incurred.

No definition available.

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

Represents the measurement periods ending with the year for which the incentive management fee is being calculated.

No definition available.

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

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

No definition available.

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

Represents the amount of amortization of the liability recorded during the period.

No definition available.

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

Related Party Transaction Amortization Of Liability Related To Property Management And Construction Supervision Fees

No definition available.

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

Represents the base management fees payable as a percentage of aggregate book value of real estate assets or transferred assets.

No definition available.

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

Represents the base management fee payable as a percentage of average closing price per share of common shares on NYSE.

No definition available.

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

Represents the base management fees payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments exceeding specified amount.

No definition available.

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

Represents the base management fees payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments up to specified amount.

No definition available.

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

Represents the base management fee payable as a percentage of average market capitalization exceeding specified amount.

No definition available.

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

Represents the amount of average market capitalization for payment of base management fee.

No definition available.

Name:	dhc_RelatedPartyTransactionBaseManagementFeePayableAverageMarketCapitalization
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the threshold amount of average market capitalization for payment of the base management fee.

No definition available.

Name:	dhc_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfAverageMarketCapitalization
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the threshold amount of other real estate investments for payment of base management fee.

No definition available.

Name:	dhc_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfOtherRealEstateInvestments
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the threshold amount of real estate investments for payment of base management fee.

No definition available.

Name:	dhc_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfRealEstateInvestments
Namespace Prefix:	dhc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Represents the incentive fee payable to related parties under the business management agreement.

No definition available.

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

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

No definition available.

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

Related Party Transaction, Incentive Management Fee Cap on Common Shares

No definition available.

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

Related Party Transaction, Incentive Management Fee, Consecutive Trading Days

No definition available.

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

Related Party Transaction, Incentive Management Fee Reduction, Total Return , Basis Spread

No definition available.

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

Related Party Transaction, Incentive Management Fee, Top Consecutive Trading Days

No definition available.

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

Represents the window or numbers of business days after any calendar year to provide notice for termination of property management agreement by the related party for performance reasons.

No definition available.

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

Represents the number of business days notice for termination of property management agreement by the related party for convenience.

No definition available.

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

Represents the incentive management fee payable as a percentage of the product of the entity's equity market capitalization and its share price appreciation plus dividends.

No definition available.

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

Related Party Transaction, Percentage Of Property Management Fees Payable Of Gross Collected Rent

No definition available.

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

Represents the period over which the related party agrees to provide certain transition services following an applicable termination of the agreement.

No definition available.

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

Represents the construction supervision fees payable to related parties under property management agreement expressed as a percentage of construction costs.

No definition available.

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

Represents the number of consecutive renewal terms of agreement that the entity has the option to renew.

No definition available.

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

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

No definition available.

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

Represents the window after a change in control to provide notice for termination of property management agreement by the related party.

No definition available.

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

Represents the remaining term assumption in years used to calculate the fee for termination of one or both of the company's amended management agreements for a performance reason.

No definition available.

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

Represents the term in years used to calculate the fee for termination of one or both of the company's amended management agreements for a performance reason.

No definition available.

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

A fee charged for services from professionals such as doctors, lawyers and accountants. The term is often expanded to include other professions, for example, pharmacists charging to maintain a medicinal profile of a client or customer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.2(a),(b),(c),(d))
-URI http://asc.fasb.org/extlink&oid=116637345&loc=SL114874292-224272

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 220
-Section 45
-Paragraph 3
-Subparagraph (k)
-URI http://asc.fasb.org/extlink&oid=118262090&loc=SL114874205-224268

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

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.

No definition available.

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

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

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

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

Name:	us-gaap_TransactionTypeAxis=dhc_AmendedAndRestateBusinessManagementAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

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

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
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Balance Type:
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Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
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