Schedule III Real Estate Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Real Estate and Accumulated Depreciation [Line Items]
Real Estate, Gross	$ 6,181,877	$ 7,305,848	$ 7,031,660
Real Estate, Other Acquisitions	232,698	28,025	117,981
Real Estate, Improvements	549,506	421,404	592,651
Real Estate, Cost of Real Estate Sold	(387,017)	(1,468,635)	(350,698)
Impairment Charges	(3,719)	(3,406)	(15,406)
Write Off of Fully Depreciated Assets	(50,064)	(101,359)	(70,340)
SEC Schedule III, Real Estate, Gross	6,523,281	6,181,877	7,305,848
Total Land, Land Improvements, Buildings and Tenant Improvements Held-for-Sale	(41,126)	(49,277)	(906,591)
SEC Schedule III, Real Estate, Excluding Held-for-Sale	6,482,155	6,132,600	6,399,257
Real Estate Accumulated Depreciation	1,302,210	1,199,608	1,505,677	$ 1,382,757
Real Estate Accumulated Depreciation, Depreciation Expense	255,419	253,683	290,279
Real Estate Accumulated Depreciation, Real Estate Sold	(102,753)	(458,393)	(97,032)
Real Estate Accumulated Depreciation, Other Deductions	(50,064)	(101,359)	(70,327)
Schedule III - Accumulated Depreciation of Assets Held-for-Sale	(18,581)	(7,183)	(270,340)
Real Estate Investment Property, Accumulated Depreciation	$ 1,283,629	$ 1,192,425	$ 1,235,337