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

No definition available.

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:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- 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 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592

Reference 2: 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=6947722&loc=d3e13537-108611

Reference 3: 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=6947722&loc=d3e13531-108611

Reference 4: 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=6927468&loc=d3e6351-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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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Data Type:	xbrli:stringItemType
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Concentration (Details)		3 Months Ended
Concentration (Details)	Mar. 31, 2012 government state property	Mar. 31, 2012 Annualized rental income California	Mar. 31, 2012 Annualized rental income Maryland	Mar. 31, 2012 Annualized rental income District of Columbia	Mar. 31, 2012 Annualized rental income New York	Mar. 31, 2012 Annualized rental income Georgia	Mar. 31, 2012 Annualized rental income Massachusetts	Mar. 31, 2012 Annualized rental income Tenant concentration U.S. Government, state governments and the United Nations	Mar. 31, 2011 Annualized rental income Tenant concentration U.S. Government, state governments and the United Nations	Mar. 31, 2012 Annualized rental income Tenant concentration U.S. Government	Mar. 31, 2011 Annualized rental income Tenant concentration U.S. Government
Concentration
Number of properties owned	71
Number of states in which acquired properties located	29
Concentration
Number of state governments	8
Concentration risk, percentage								92.20%	93.00%	68.40%	77.20%
Annualized Rental income percent		0.132	0.127	0.100	0.093	0.080	0.069