Dispositions (Asseets and liabilities related to dispositions) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Dispositions
Real Estate, Net	$ 2,642	$ 29,561
Other Assets	2,928	7,459
Assets related to discontinued operations	5,570	37,020
Other Liabilities	2,870	12,470
Liabilities related to discontinued operations	2,870	12,470
Income from discontinued operations:
Total revenues	3,998	27,831	$ 395,786
Total expenses	1,435	17,651	274,107
Income from discontinued operations before gain on sale of real estate	2,563	10,180	121,679
Gain (Loss) from disposal of real estate	5,074	65,396	507,192
Impairment losses	(465)	(256)	(26,518)
UE spin-off transaction related costs	0	(22,972)	(14,956)
Pretax income from discontinued operations	7,172	52,348	587,397
Income tax expense	0	(86)	(1,721)
Income from Discontinued Operations	7,172	52,262	585,676
Cash flows related to discontinued Operations:
Cash flows from operating activities, discontinued operations	455	(33,462)	123,837
Cash flows from investing activities, discontinued operations	$ 2,785	$ 346,865	$ (180,019)