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Concentration of Rental Revenue (Details) | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Concentration Risk |  |  |  |  |  |
Number of regions with real estate operations which are not located in the Mid-Atlantic region of the United States | 3 |  |  |  |  |
Rental revenue | Tenants |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage required for qualification as major customer | 5.00% |  |  |  |  |
Number of tenants from which the entity has recognized the most rental revenue aggregated for revenue concentration disclosure | 5 |  |  |  |  |
Rental revenue | Tenants | United States Government |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue | 18.00% |  | 18.00% |  | 17.00% |
Rental revenue | Tenants | Northrop Grumman Corporation |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue | 8.00% | [1] | 7.00% | [1] | 8.00% | [1]
Rental revenue | Tenants | Booz Allen Hamilton, Inc. |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue | 6.00% |  | 6.00% |  | 6.00% |
Rental revenue | Tenants | Computer Sciences Corporation |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue | 5.00% | [1] | 5.00% | [1] |  |
Rental revenue | Tenants | Five largest tenants |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue | 41.00% |  | 39.00% |  | 38.00% |
Construction contract revenue | United States Government |  |  |  |  |  |
Concentration Risk |  |  |  |  |  |
Percentage of revenue | 90.00% |  | 90.00% |  | 90.00% |
[1] | Includes affiliated organizations and agencies and predecessor companies.

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- Definition Represents the number of regions with real estate operations which are not located in the Mid-Atlantic region of the United States. + References No definition available. + Details
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- Definition Represents the number of tenants from which the entity has recognized the most rental revenue aggregated for revenue concentration disclosure. + References No definition available. + Details
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- Definition Threshold percentage which the entity uses for disclosure. + References No definition available. + Details
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- 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 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13537-108611 Reference 2: 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 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=28364263&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
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