Subsequent Events (Details) (USD $)	9 Months Ended		0 Months Ended		0 Months Ended				0 Months Ended		3 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Oct. 05, 2014 Six States Office Building Subsequent Event Property	Oct. 05, 2014 Six States Office Building Subsequent Event	Sep. 26, 2014 Common Stock	Feb. 11, 2014 Common Stock	Jan. 10, 2014 Common Stock	Sep. 26, 2014 Common Stock	Oct. 02, 2014 Common Stock Subsequent Event	Oct. 02, 2014 Common Stock Subsequent Event	Mar. 31, 2015 Scenario, Forecast Subsequent Event
Subsequent Event [Line Items]
Issuance of shares of common stock (in shares)	22,216,900				10,000,000	1,325,000	10,500,000		1,500,000
Stock offering price (dollars per share)						$ 18.15	$ 18.15	$ 18.60		$ 18.60
Number of properties under agreement to sell			19
Gross sales price of assets under agreement to sell				$ 237,000,000
Gross purchase price of asset	$ 282,352,000	$ 187,442,000									$ 157,000,000