Subsequent Events (Details) (USD $)	2 Months Ended	12 Months Ended		25 Months Ended					0 Months Ended			0 Months Ended		2 Months Ended
	Feb. 27, 2013	Dec. 31, 2012 property	Dec. 31, 2011 property	Dec. 31, 2012	Dec. 31, 2012 2012 Acquisitons [Member] sqft property	Feb. 22, 2013 2013 Acquisitons [Member] sqft property	Dec. 31, 2012 Vacant [Member] Real Estate [Member] property	Dec. 31, 2011 Vacant [Member] Real Estate [Member] property	Jan. 29, 2013 Follow on Offering, Underwriter [Member] [Member]	Jan. 29, 2013 Follow on Offering, Public [Member] [Member]	Jan. 24, 2013 Follow on Offering, Public [Member] [Member]	Jan. 29, 2013 Follow on Offering [Member]	Jan. 24, 2013 Follow on Offering [Member]	Feb. 27, 2013 At the Market Offering [Member]	Feb. 22, 2013 Property Acquisition [Member] property
Subsequent Event [Line Items]
Shares Issued (in shares)									270,000	1,800,000		2,070,000		61,000
Maximum Amount of Offering from Universal Shelf Registration Statement		$ 500,000,000		$ 500,000,000
Weighted Average Price per Share											13.47			0
Proceeds from Issuance of Common Stock		118,900,000										26,500,000		800,000
Remaining Equity Offering, At the Market Offering														59,200,000
Maximum Equity Offering, At the Market Offering [Line Items]	60,000,000
Common Stock, Par or Stated Value Per Share		$ 0.01	$ 0.01	$ 0.01									$ 0.01
Number of Real Estate Properties					146	151	1	2
Square feet of acquired property					2,412,104	2,471,138
Business Acquisition, Cost of Acquired Entity, Purchase Price		1,200,000		1,200,000	268,625,000	290,535,000
Number of Businesses Acquired		58	88	146											5
Area of Real Estate Property, Acquisitions															59,034
Real Estate Investment Property, at Cost, Acquisitions															$ 21,910,000