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
	Mar. 31, 2018	Mar. 31, 2017
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	$ 14,102	$ 10,431
Revenues	5	46,239
Operating Expenses	(13)	(14,996)
Depreciation and amortization	0	(19,534)
Operating (loss) income	(8)	11,709
Interest expense	0	(6,343)
(Loss) income before gain on sales and income tax	(8)	5,366
Gain on sale of depreciable properties	132	0
Income from discontinued operations	$ 124	5,366
Discontinued Operations [Member]
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements		$ 12,600