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
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
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=84177426&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=77997519&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=84177426&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=77997519&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

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=gov_RealEstateRevenueNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_VA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_MD
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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- Details

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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- 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_SegmentContinuingOperationsMember
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Concentration (Details)	12 Months Ended
Concentration (Details)	Dec. 31, 2017 building state property government_tenant state_government	Dec. 31, 2016	Dec. 31, 2015
Concentration Risk [Line Items]
Number of state governments \| state_government	13
Number of other governments \| government_tenant	5
Annualized rental income, excluding properties classified as discontinued operations \| Virginia
Concentration Risk [Line Items]
Annualized Rental income percent	23.20%
Annualized rental income, excluding properties classified as discontinued operations \| District of Columbia
Concentration Risk [Line Items]
Concentration risk, percentage	43.30%
Annualized Rental income percent	17.70%
Annualized rental income, excluding properties classified as discontinued operations \| Maryland
Concentration Risk [Line Items]
Annualized Rental income percent	14.90%
Annualized rental income, excluding properties classified as discontinued operations \| California
Concentration Risk [Line Items]
Annualized Rental income percent	9.60%
Annualized rental income, excluding properties classified as discontinued operations \| Georgia
Concentration Risk [Line Items]
Annualized Rental income percent	5.60%
Annualized rental income, excluding properties classified as discontinued operations \| New York
Concentration Risk [Line Items]
Annualized Rental income percent	4.40%
Annualized rental income, excluding properties classified as discontinued operations \| Massachusetts
Concentration Risk [Line Items]
Annualized Rental income percent	3.20%
Annualized rental income, excluding properties classified as discontinued operations \| Tenant concentration \| U S Government, State Governments, and Other Governments
Concentration Risk [Line Items]
Concentration risk, percentage	62.60%	87.90%	92.80%
Annualized rental income, excluding properties classified as discontinued operations \| Tenant concentration \| U.S. Government
Concentration Risk [Line Items]
Concentration risk, percentage	43.50%	60.60%	67.00%
Continuing operations
Concentration Risk [Line Items]
Number of properties owned \| property	108
Number of buildings \| building	167
Number of states in which acquired properties located \| state	30