Fair Value of Assets and Liabilities - Additional Information (Details) $ in Thousands		12 Months Ended
Oct. 02, 2017 USD ($) mortgage_note loan	Dec. 31, 2017 loan
Debt Instrument [Line Items]
Number of loans assumed \| loan		8
First Potomac Realty Trust
Debt Instrument [Line Items]
Number of loans assumed \| loan	5
Long term debt acquired	$ 167,936
FPO Mortgage \| Mortgages \| First Potomac Realty Trust
Debt Instrument [Line Items]
Number of loans assumed \| mortgage_note	5
Long term debt acquired	$ 167,548
Fair value of debt	$ 167,936

Represents the number of mortgage loans on real estate assumed in acquisitions during the period.

No definition available.

Name:	gov_MortgageLoansOnRealEstateAssumedInAcquisitionsNumberOfLoans
Namespace Prefix:	gov_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472

+ Details

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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

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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Namespace Prefix:
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- Details

Name:	us-gaap_DebtInstrumentAxis=gov_FPOMortgageMember
Namespace Prefix:
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Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_MortgagesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: