Subsequent Events - (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended	6 Months Ended	0 Months Ended	1 Months Ended	30 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 Property	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2012 Centennial, Colorado Acquisition, July 31, 2012	Jul. 31, 2012 Subsequent event Centennial, Colorado Acquisition, July 31, 2012 Property	Jul. 31, 2012 Subsequent event Centennial, Colorado Acquisition, July 31, 2012	Aug. 09, 2012 Initial public offering Subsequent event Issuance of equity
Subsequent Event [Line Items]
Issuance of common stock			$ 53,810,093		$ 67,300,000				$ 85,500,000
Stock issued during period, shares, dividend reinvestment plan									8.6
Number of businesses acquired			2				1
Aggregate purchase price	8,596,083	32,850,000	8,596,083	32,850,000	8,596,083		32,600,000	32,600,000
Acquisition costs	$ 304,501	$ 718,839	$ 304,501	$ 718,839		$ 43,000		$ 651,000