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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements			$ 34,350	$ 39,169
Revenues	$ 4,622	$ 44,906	86,026	129,087
Operating Expenses	(1,613)	(14,466)	(27,780)	(41,602)
Depreciation and amortization	(37)	(18,868)	(25,886)	(56,158)
Operating income	2,972	11,572	32,360	31,327
Interest expense	(409)	(7,323)	(14,613)	(22,265)
Income before gain on sales	2,563	4,249	17,747	9,062
Gain on sale of depreciable properties	120,179	319	1,229,270	485
Income from discontinued operations before income taxes	122,742	4,568	1,247,017	9,547
Income tax benefit (expense)	876	0	(10,736)	0
Income from discontinued operations	$ 123,618	$ 4,568	1,236,281	9,547
Discontinued Operations [Member]
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements			$ 20,800	$ 62,400