Indebtedness - Additional Information (Details) $ in Thousands	9 Months Ended
Sep. 30, 2018 USD ($) property loan building
Debt Disclosure [Abstract]
Number of properties secured by mortgage notes \| property	8
Number of buildings secured by mortgage notes \| building	8
Aggregate net book value of secured properties	$ 417,842
Number of assumed secured mortgage loans \| loan	8
Aggregate principal amount on secured properties	$ 180,416

Represents the aggregate net book value of real estate properties serving as a collateral for debt, as of the balance sheet date.

No definition available.

Name:	gov_AggregateNetBookValueOfRealEstatePropertiesCollateralized
Namespace Prefix:	gov_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The aggregate principal amount on real estate properties serving as collateral for debt as of the balance sheet date.

No definition available.

Name:	gov_AggregatePrincipalAmountOfRealEstatePropertiesCollateralized
Namespace Prefix:	gov_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

The number of buildings serving as collateral for debt as of the balance sheet date.

No definition available.

Name:	gov_NumberOfBuildingsCollateralized
Namespace Prefix:	gov_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Represents the number of real estate properties serving as a collateral for debt, as of the balance sheet date.

No definition available.

Name:	gov_NumberOfRealEstatePropertiesCollateralized
Namespace Prefix:	gov_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

No definition available.

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