Real Estate Facilities (Narrative) (Details) (USD $)	3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Bayshore Commons [Member]	Dec. 20, 2013 Bayshore Commons [Member] sqft item	Mar. 31, 2014 Dallas Multi Tenant Flex Buildings [Member]	Nov. 08, 2013 Dallas Multi Tenant Flex Buildings [Member] sqft item	Mar. 31, 2014 Dallas Multi-Tenant Flex Parks [Member]	Oct. 15, 2013 Dallas Multi-Tenant Flex Parks [Member] sqft property acre	Mar. 31, 2014 Dallas Industrial Park [Member]	Jul. 26, 2013 Dallas Industrial Park [Member] sqft item	Mar. 31, 2014 Northern Virginia Redeveloped Land [Member] sqft	Dec. 31, 2013 Northern Virginia Redeveloped Land [Member]
Real Estate Facilities [Line Items]
Acquisition/disposal date of real estate			Dec. 20, 2013		Nov. 08, 2013		Oct. 15, 2013		Jul. 26, 2013
Number of buildings acquired				8		9				18
Number of parks acquired								4
Number of acres acquired								4
Leasable space (in square feet)				340,000		245,000		559,000		389,000
Purchase price				$ 60,500,000		$ 12,400,000		$ 27,900,000		$ 14,800,000
Area of redevelopment of real estate property											125,000
Land and building held for development	24,618,000	23,990,000									16,800,000	16,200,000
Capitalized cost	628,000
Captialized interest expense	$ 224,000