Acquisitions, Dispositions, Discontinued Operations and Assets Held for Sale Acquisitions, Dispositions, Discontinued Operations and Assets Held for Sale (Assets and Liabilities Held for Sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Long Lived Assets Held-for-sale [Line Items]
Land	$ 989,097	$ 989,247
Buildings and improvements	5,956,361	5,911,432
Real estate assets, at cost, total	6,945,458	6,900,679
Accumulated depreciation	(1,855,678)	(1,780,694)
Net operating real estate assets	5,089,780	5,119,985
Properties under development, including land	446,740	486,918
Properties held for sale, including land	$ 0	239,063
Discontinued Operations, Held-for-sale or Disposed of by Sale [Member]
Long Lived Assets Held-for-sale [Line Items]
Land		59,438
Buildings and improvements		373,419
Real estate assets, at cost, total		432,857
Accumulated depreciation		(197,996)
Net operating real estate assets		234,861
Properties under development, including land		4,202
Properties held for sale, including land		239,063
Other assets related to properties held for sale		1,191
Total assets held for sale		240,254
Liabilities related to assets held for sale		$ 1,654