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
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=6927468&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 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13537-108611

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=6927468&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 20

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13531-108611

+ 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_RisksAndUncertaintiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Concentration (Details)	12 Months Ended
Concentration (Details)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Concentration
Number of properties owned	84
Number of states in which acquired properties located	32
Concentration
Number of state governments	10
Annualized rental income \| California
Concentration
Annualized Rental income percent	0.120
Annualized rental income \| Maryland
Concentration
Annualized Rental income percent	0.125
Annualized rental income \| District of Columbia
Concentration
Annualized Rental income percent	0.103
Annualized rental income \| Georgia
Concentration
Annualized Rental income percent	0.095
Annualized rental income \| New York
Concentration
Annualized Rental income percent	0.089
Annualized rental income \| Massachusetts
Concentration
Annualized Rental income percent	0.061
Annualized rental income \| Tenant concentration \| U.S. Government, state governments and the United Nations
Concentration
Concentration risk, percentage	93.90%	91.90%	93.00%
Annualized rental income \| Tenant concentration \| U.S. Government
Concentration
Concentration risk, percentage	71.70%	69.60%	78.20%