Concentration (Details)	6 Months Ended
Jun. 30, 2017 property government_tenant state_government state building	Jun. 30, 2016 property building
Concentration
Number of state governments \| state_government	13
Number of other governments \| government_tenant	4
Number of properties \| property	74
Number of buildings \| building	96
Number of states in which acquired properties located \| state	31
Annualized rental income, excluding properties classified as discontinued operations \| Virginia
Concentration
Annualized Rental income percent	14.80%
Annualized rental income, excluding properties classified as discontinued operations \| California
Concentration
Annualized Rental income percent	14.80%
Annualized rental income, excluding properties classified as discontinued operations \| District of Columbia
Concentration
Annualized Rental income percent	9.50%
Annualized rental income, excluding properties classified as discontinued operations \| Georgia
Concentration
Annualized Rental income percent	8.60%
Annualized rental income, excluding properties classified as discontinued operations \| New York
Concentration
Annualized Rental income percent	7.20%
Annualized rental income, excluding properties classified as discontinued operations \| Maryland
Concentration
Annualized Rental income percent	7.00%
Annualized rental income, excluding properties classified as discontinued operations \| Massachusetts
Concentration
Annualized Rental income percent	4.90%
Annualized rental income, excluding properties classified as discontinued operations \| Tenant concentration \| U.S. Government, state governments and Other Three Government
Concentration
Concentration risk percentage	87.60%	92.70%
Annualized rental income, excluding properties classified as discontinued operations \| Tenant concentration \| U.S. Government
Concentration
Concentration risk percentage	59.60%	64.10%
Discontinued operations
Concentration
Number of properties \| property	1	1
Number of buildings \| building	1	1

The number of buildings owned as of the balance sheet date.

No definition available.

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

- Definition

Represents the number of other governments that are tenants of the entity.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of state governments that are tenants of the entity.

+ References

No definition available.

+ Details

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

- Definition

The number of states in which real estate owned by the entity is located as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

This element represents the percentage of rental income in each state.

+ References

No definition available.

+ Details

Name:	gov_RealEstateRevenuePercent
Namespace Prefix:	gov_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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_ConcentrationRiskLineItems
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Period Type:	duration

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfRealEstateProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

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- Details

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- Details

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Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_MajorCustomersAxis=gov_USGovernmentStateGovernmentsAndOtherGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_MajorCustomersAxis=gov_USGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_StatementOperatingActivitiesSegmentAxis=us-gaap_SegmentDiscontinuedOperationsMember
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