Summary of Significant Accounting Policies - Debt Issuance Costs (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Amortization of deferred financing fees
Amortization expense in 2021	$ 8,956
Amortization expense in 2022	5,683
Amortization expense in 2023	5,142
Amortization expense in 2024	5,008
Amortization expense in 2025	3,038
Amortization expense thereafter	13,211
Unsecured Term Loans, Senior Notes, and Mortgage Notes Payable
Debt Instrument
Deb issuance costs, gross	53,496	$ 41,452
Accumulated amortization, debt issuance costs gross	15,589	16,887
Revolving Credit Facility
Debt Instrument
Deb issuance costs, gross	19,332	17,170
Accumulated amortization, debt issuance costs gross	$ 16,201	$ 13,944

No definition available.

Name:	dhc_DeferredFinanceCostsFutureAmortizationExpenseAbstract
Namespace Prefix:	dhc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the amount of amortization of deferred financing fees expected to be recognized after the fifth succeeding fiscal year.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of amortization of deferred financing fees expected to be recognized during year five of the five succeeding fiscal years.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of amortization of deferred financing fees expected to be recognized during year four of the five succeeding fiscal years.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of amortization of deferred financing fees expected to be recognized during year one of the five succeeding fiscal years.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of amortization of deferred financing fees expected to be recognized during year three of the five succeeding fiscal years.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of amortization of deferred financing fees expected to be recognized during year two of the five succeeding fiscal years.

+ References

No definition available.

+ Details

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

- Definition

Amount of accumulated amortization of debt issuance costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28555-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_AccumulatedAmortizationDeferredFinanceCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

No definition available.

+ Details

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

- Definition

Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=dhc_UnsecuredTermLoansSeniorNotesandMortgageNotesPayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: