Property Dispositions, Assets Held for Sale, and Discontinued Operations (Assets Held for Sale) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total real estate assets held for sale, net	$ 26,111		$ 26,111		$ 46,354
Straight-line rent receivables	1,904		1,904		2,643
Deferred lease costs, less accumulated amortization of $919 and $2,335 as of June 30, 2015 and December 31, 2014, respectively	1,802		1,802		2,140
Accumulated amortization on deferred lease costs	919		919		2,335
Total other assets held for sale, net	3,706		3,706		4,783
Impairment loss on real estate asset	5,354	$ 0	5,354	$ 0
Eastpoint I and II [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment loss on real estate asset	5,400
Land [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate assets held for sale, net:	4,281		4,281		5,798
Building and Building Improvements [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate assets held for sale, net:	21,633		21,633		40,546
Accumulated depreciation (building improvements)	12,828		12,828		23,009
Construction in Progress [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Real estate assets held for sale, net:	$ 197		$ 197		$ 10