Discontinued Operations and Assets Held for Sale (Table Illustration of Discontinued Operations in Income Statement) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	$ 61,900	$ 98,821	$ 91,798
Revenues	32,549	120,884	159,096
Operating expenses	(12,498)	(47,123)	(62,048)
Depreciation and Amortization, Discontinued Operations	(3,517)	(38,342)	(55,594)
Operating income	16,534	35,419	41,454
Interest expense	(5,595)	(24,348)	(37,649)
Income (loss) before gain on sales	10,939	11,071	3,805
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax	424,892	22,763	133,242
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	435,831	33,834	137,047
Discontinued Operation, Tax Effect of Discontinued Operation	(3,175)	(2,969)	0
Income from discontinued operations	432,656	30,865	137,047
Discontinued Operations [Member]
Discontinued Operations
Payments For Second Generation Tenant Improvements Leasing Costs And Building Improvements	$ 7,400	$ 32,500	$ 21,700