Real Estate Discontinued Operations (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012 sqft	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011 sqft
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rentable square feet	214,000				3,272,000
Contract purchase price	$ 14,300,000		$ 14,300,000		$ 409,700,000
Revenues	1,088,000	7,978,000	3,560,000	29,688,000
Property expenses	(419,000)	(2,281,000)	(1,327,000)	(9,012,000)
Real estate impairment	0	0	0	(599,000)
Depreciation and amortization	(91,000)	(1,314,000)	(867,000)	(8,353,000)
Interest expense	(64,000)	(296,000)	(191,000)	(891,000)
Income from operations of properties sold or held for sale	514,000	4,087,000	1,175,000	10,833,000
Less: Net income attributable to noncontrolling interests in subsidiaries	0	(28,000)	0	(85,000)
Income from operations of properties sold or held for sale attributable to the controlling interests	514,000	4,059,000	1,175,000	10,748,000
1700 Research Boulevard [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property type	Office		Office
Rentable square feet	101,000
Contract purchase price	14,300,000		14,300,000
Income from operations of properties sold or held for sale	106,000	150,000	225,000	521,000
Plumtree Medical Center [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Real Estate Properties Held for Sale	1
Property type	Medical Office		Medical Office
Rentable square feet	33,000
Income from operations of properties sold or held for sale	88,000	13,000	117,000	53,000
Atrium Building [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Real Estate Properties Held for Sale	1
Property type	Office		Office
Rentable square feet	80,000
Income from operations of properties sold or held for sale	320,000	269,000	833,000	737,000
Industrial Portfolio Member
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property type			Industrial/Office		Industrial/Office	[1]
Rentable square feet					3,092,000	[1]
Contract purchase price					350,900,000	[1]
Number of office assets					2
Income from operations of properties sold or held for sale	0	3,655,000	0	9,990,000
Dulles Station, Phase I [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Property type			Office		Office
Rentable square feet					180,000
Contract purchase price					58,800,000
Income from operations of properties sold or held for sale	0	0	0	(468,000)
Asset impairment charges				$ 600,000

[1] The Industrial Portfolio consists of every property in our industrial segment and two office properties (the Crescent and Albemarle Point). On September 2, 2011 we closed on the sale of industrial properties (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) and two office properties (Crescent and Albemarle Point). On October 3, 2011, we closed on the sale of Northern Virginia Industrial Park II. On November 2, 2011, we closed on the sale of 6100 Columbia Park Road and Dulles Business Park I and II.