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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements			$ 26,337	$ 20,112
Revenues	$ 27	$ 35,165	32	81,404
Operating Expenses	4	(11,170)	(9)	(26,166)
Depreciation and amortization	0	(6,315)	0	(25,849)
Operating income	31	17,680	23	29,389
Interest expense	0	(6,585)	0	(14,204)
Income before gain on sales and income tax	31	11,095	23	15,185
Gain on sale of depreciable properties	2,889	1,109,091	3,021	1,109,091
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	2,920	1,120,186	3,044	1,124,276
Income from discontinued operations	$ 2,920	$ 1,108,573	$ 3,044	1,112,663
Discontinued Operations [Member]
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements				$ 20,600