Annual report pursuant to Section 13 and 15(d)

Nature Of Business (Details)

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Nature Of Business (Details) (USD $)
12 Months Ended 0 Months Ended 12 Months Ended 3 Months Ended 0 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended 0 Months Ended 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Aug. 31, 2012
Research Boulevard 1700 [Member]
Dec. 20, 2012
Plumtree Medical Center [Member]
Sep. 02, 2011
Dulles Station, Phase I [Member]
Dec. 31, 2011
Dulles Station, Phase I [Member]
Dec. 31, 2011
Dulles Station II [Member]
Aug. 05, 2011
Industrial Portfolio [Member]
Dec. 31, 2011
Industrial Portfolio [Member]
Jun. 18, 2010
Parklawn Portfolio [Member]
Dec. 31, 2010
Parklawn Portfolio [Member]
Dec. 21, 2010
The Ridges [Member]
Dec. 31, 2010
The Ridges [Member]
Dec. 22, 2010
Ammendale I and II and Amvax [Member]
Dec. 31, 2010
Ammendale I and II and Amvax [Member]
Dec. 31, 2012
Taxable Reit Subsidiary [Member]
Dec. 31, 2011
Taxable Reit Subsidiary [Member]
Aug. 05, 2011
Office Building [Member]
Industrial Portfolio [Member]
properties
Aug. 05, 2011
Office Building [Member]
Parklawn Portfolio [Member]
properties
Nature of Business [Line Items]                                        
Percentage of Distribution of Ordinary Taxable Income 90.00%                                      
Gain and Sale $ 5,124,000 $ 97,491,000 $ 21,599,000 $ 3,724,000 [1] $ 1,400,000 $ 0 $ 0   $ 97,491,000 $ 97,491,000 $ 7,942,000 $ 7,942,000 [1] $ 4,441,000 $ 4,441,000 $ 9,216,000 $ 9,216,000        
Number of real estate properties                                     2 3
Federal and state income tax liabilities recognized 0 1,138,000 0                                  
Real estate impairment 2,097,000 14,526,000 0       600,000 14,500,000                        
Deferred Tax Assets 5,700,000                                      
Deferred Tax Assets, Net                                 0 100,000    
Deferred Tax Liabilities                                 $ 600,000 $ 500,000    
Ordinary income 72.00% 60.00% 55.00%                                  
Return of capital 26.00% 17.00% 31.00%                                  
Qualified dividends 0.00% 5.00% 0.00%                                  
Unrecaptured Section 1250 gain 2.00% 13.00% 11.00%                                  
Capital gain 0.00% 5.00% 3.00%                                  
[1] The Industrial Portfolio consists of every property in our industrial segment and two office properties (the Crescent and Albemarle Point), and we closed on the sale on three separate dates. On September 2, 2011, we closed on the sale of the two office properties (the Crescent and Albemarle Point) and 8880 Gorman Road, Dulles South IV, Fullerton Business Center, Hampton Overlook, Alban Business Center, Pickett Industrial Park, Northern Virginia Industrial Park I, 270 Technology Park, Fullerton Industrial Center, Sully Square, 9950 Business Parkway, Hampton South and 8900 Telegraph Road. On October 3, 2011, we closed the sale of Northern Virginia Industrial Park II. On November 1, 2011, we closed on the sale of 6100 Columbia Park Road and Dulles Business Park I and II.