Discontinued Operations and Assets Held for Sale (Table Illustration of Discontinued Operations in Income Statement) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Discontinued Operations
Revenues	$ 0	$ 117	$ 87,185
Operating expenses	0	(9)	(28,102)
Depreciation and Amortization, Discontinued Operations	0	0	(25,911)
Operating income	0	108	33,172
Interest expense	0	0	(14,736)
Income before gain on sales and income taxes	0	108	18,436
Gain on sale of properties	445	3,792	1,357,778
Income from discontinued operations before income taxes	445	3,900	1,376,214
Income tax expense	0	0	(12,465)
Income from discontinued operations	445	3,900	1,363,749
Payments For Second Generation Tenant Improvements Leasing Costs, Building Improvements and development costs	$ 47,549	$ 53,474	52,554
Discontinued Operations [Member]
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs, Building Improvements and development costs			$ 20,900