Acquisitions (Schedule of Real Estate Property Acquisitions) (Details) (Northern Virginia, Loudoun Parkway North [Member], USD $) In Millions	6 Months Ended
	Jun. 30, 2011
Northern Virginia, Loudoun Parkway North [Member]
Acquisition, Date Acquired	April 15, 2011	[1]
Acquisition, Amount	$ 17.3	[1]

[1] (1) Represents vacant land which is not included in our operating property count.