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, 2016 USD ($) buildings	Dec. 31, 2015 USD ($)
Held for Sale Assets in Continuing and Discontinued Operations
Total assets held-for-sale	$ 64,161	$ 45,801
Total liabilities held-for-sale	$ 1,388	972
Continuing Operations, Number of In-service Properties Held for Sale | buildings	5
Continuing Operations [Member]
Held for Sale Assets in Continuing and Discontinued Operations
Land and Land Improvements Held-for-Sale	$ 18,592	9,797
Buildings and Tenant Improvements Held-for-Sale	48,456	39,480
Accumulated Depreciation of Assets Held-for-Sale	(12,014)	(7,183)
Lease Related Assets, Held for Sale	7,546	3,293
Other assets	1,581	414
Total assets held-for-sale	64,161	45,801
Accrued expenses	814	322
Other liabilities	574	650
Total liabilities held-for-sale	$ 1,388	$ 972