Discontinued Operations and Assets Held for Sale (Table Illustration of Discontinued Operations in Income Statement) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	$ 59,349	$ 61,900	$ 98,821
Revenues	983	32,549	120,884
Operating expenses	8	(12,498)	(47,123)
Depreciation and Amortization, Discontinued Operations	0	(3,517)	(38,342)
Operating income	991	16,534	35,419
Interest expense	0	(5,595)	(24,348)
Income (loss) before gain on sales	991	10,939	11,071
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax	1,016	424,892	22,763
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	2,007	435,831	33,834
Discontinued Operation, Tax Effect of Discontinued Operation	0	(3,175)	(2,969)
Income from discontinued operations	$ 2,007	432,656	30,865
Discontinued Operations [Member]
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements		$ 7,400	$ 32,500