Real Estate Assets, Discontinued Operations and Assets Held for Sale (Table Illustration of Discontinued Operations in Income Statement) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements			$ 34,311	$ 34,350
Revenues	$ 85	$ 4,622	117	86,026
Operating Expenses	0	(1,613)	(9)	(27,780)
Depreciation and amortization	0	(37)	0	(25,886)
Operating income	85	2,972	108	32,360
Interest expense	0	(409)	0	(14,613)
Income before gain on sales and income tax	85	2,563	108	17,747
Gain on sale of depreciable properties	136	120,179	3,157	1,229,270
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	221	122,742	3,265	1,247,017
Discontinued Operation, Tax Effect of Discontinued Operation	0	876	0	(10,736)
Income from discontinued operations	$ 221	$ 123,618	$ 3,265	1,236,281
Discontinued Operations [Member]
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements				$ 20,800