Real Estate Assets, Discontinued Operations and Assets Held for Sale (Aggregate Balance Sheet of Properties Held for Sale Included in Discontinued Operations) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($) buildings	Dec. 31, 2018 USD ($)
Held for Sale Assets in Continuing and Discontinued Operations
Continuing Operations, Number of In-service Properties Held for Sale | buildings	2
Total assets held-for-sale	$ 20,472	$ 1,082
Total liabilities held-for-sale	633	0
Continuing Operations [Member]
Held for Sale Assets in Continuing and Discontinued Operations
Land and Land Improvements Held-for-Sale	5,956	0
Buildings and Tenant Improvements Held-for-Sale	16,681	0
Inventory, Land Held-for-sale	4,849	1,966
Accumulated Depreciation of Assets Held-for-Sale	(7,949)	(884)
Deferred leasing and other costs, net	318	0
Other assets	617	0
Total assets held-for-sale	20,472	1,082
Disposal Group, Including Discontinued Operation, Accrued Liabilities	556	0
Disposal Group, Including Discontinued Operation, Other Liabilities	77	0
Total liabilities held-for-sale	$ 633	$ 0