Commitments And Contingencies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended		0 Months Ended
	Dec. 31, 2014 property sqft	Dec. 31, 2013	Feb. 11, 2015 item sqft property
Other Commitments [Line Items]
Number of properties	126		11
Area of real estate property	9,300,000.0		641,593.0
Total aggregate initial investment	$ 236.7	$ 212.4
Non-binding Letter Of Intent [Member]
Other Commitments [Line Items]
Number of non-binding letters of intent			1
Number of properties			1
Area of real estate property			34,200.0
Total aggregate initial investment			3.2
Outstanding Contract With Third Party [Member]
Other Commitments [Line Items]
Outstanding contracts with a third-party sellers			5
Number of properties			5
Area of real estate property			641,593.0
Washington DC and Baltimore [Member]
Other Commitments [Line Items]
Number of properties	1		1
Area of real estate property			115,287.0
Washington DC and Baltimore [Member] | Outstanding Contract With Third Party [Member]
Other Commitments [Line Items]
Outstanding contracts with a third-party sellers			1
Number of properties			1
Area of real estate property			84,961.0
Total aggregate initial investment			$ 11.2