Number of Trustees

No definition available.

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

- Definition

The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockPricePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares used to settle grantee's tax withholding obligation for award under share-based payment arrangement.

+ References

No definition available.

+ Details

Name:	us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

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

- Details

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

Shareholders' Equity - Share Awards and Purchases (Details)	Sep. 21, 2020 $ / shares shares	Sep. 17, 2020 $ / shares shares	Jun. 30, 2020 $ / shares shares	May 19, 2020 trustee $ / shares shares	Mar. 13, 2020 $ / shares shares	Jan. 09, 2020 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares (in shares)		360,000		60,000
Price Per Share (in dollars per share) \| $ / shares		$ 3.77		$ 2.94
Trustees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares (in shares)				10,000
Number of trustees \| trustee				6
Employees Of RMR LLC
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares (in shares)		360,000
Former Employees Of RMR LLC
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchased during period (in shares)	42,180		1,757		1,500	1,938
Shares purchased for tax withholding and payment obligations (in dollars per share) \| $ / shares	$ 3.38		$ 4.43		$ 3.79	$ 8.10