Real Estate Assets (Details) ft² in Thousands, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2015 USD ($) ft²	Mar. 31, 2015 USD ($) property	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) ft²	Jun. 30, 2014 USD ($)
Acquisitions [Abstract]
Contingent consideration in connection with the acquisition of land				$ 900	$ 0
Dispositions [Abstract]
Gain on disposition of property	$ 2,412		$ 5,947	$ 3,569	$ 5,947
Atlanta, GA Land Acquisition [Member] (6/2015) [Member]
Acquisitions [Abstract]
Purchase price of acquisition	5,200
Contingent consideration in connection with the acquisition of land	$ 900
Orlando, FL Building Acquisition [Member] (6/2015) [Member]
Acquisitions [Abstract]
Percentage of equity interest acquired in unconsolidated affiliate (in hundredths)	77.20%			77.20%
Acquisition rentable square feet (in sq. ft.) | ft²	168			168
Fair value of debt assumed in connection with the acquisition	$ 19,300			$ 19,300
Acquisition-related costs	100
Building Dispositions [Member]
Dispositions [Abstract]
Number of buildings sold | property		2
Purchase price of real estate		$ 3,500
Gain on disposition of property		400
Land Dispositions [Member]
Dispositions [Abstract]
Purchase price of real estate	500	2,500
Gain on disposition of property	$ 200	$ 800