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	3 Months Ended
	Mar. 31, 2017 USD ($) buildings	Dec. 31, 2016 USD ($)
Held for Sale Assets in Continuing and Discontinued Operations
Total assets held-for-sale	$ 81,563	$ 51,627
Total liabilities held-for-sale	$ 2,708	1,661
Continuing Operations, Number of In-service Properties Held for Sale | buildings	11
Continuing Operations [Member]
Held for Sale Assets in Continuing and Discontinued Operations
Land and Land Improvements Held-for-Sale	$ 8,874	3,631
Buildings and Tenant Improvements Held-for-Sale	76,073	37,495
Inventory, Land Held-for-sale	0	22,657
Accumulated Depreciation of Assets Held-for-Sale	(13,632)	(18,581)
Lease Related Assets, Held for Sale	7,257	3,091
Other assets	2,991	3,334
Total assets held-for-sale	81,563	51,627
Accrued expenses	1,396	1,363
Other liabilities	1,312	298
Total liabilities held-for-sale	$ 2,708	$ 1,661