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	12 Months Ended
	Mar. 31, 2021 USD ($) buildings	Dec. 31, 2020 USD ($) buildings
Held for Sale Assets in Continuing and Discontinued Operations
Continuing Operations, Number of In-service Properties Held for Sale | buildings	0
Continuing Operations, Number of Real Estate Properties Sold | buildings	2	7
Total Properties Sold or Classified as Held for Sale | buildings	9
Total assets held-for-sale	$ 0	$ 67,946
Total liabilities held-for-sale	0	7,740
Continuing Operations [Member]
Held for Sale Assets in Continuing and Discontinued Operations
Land and Land Improvements Held-for-Sale	0	27,954
Buildings and Tenant Improvements Held-for-Sale	0	44,800
Accumulated Depreciation of Assets Held-for-Sale	0	(5,976)
Deferred leasing and other costs, net	0	936
Other assets	0	232
Total assets held-for-sale	0	67,946
Accrued Expenses Held-for-Sale	0	660
Other Liabilities Held-for-Sale	0	7,080
Total liabilities held-for-sale	$ 0	$ 7,740