Schedule III Real Estate Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate and Accumulated Depreciation [Line Items]
Real Estate, Gross	$ 6,612,229	$ 6,523,281	$ 6,181,877
Real Estate, Other Acquisitions	327,318	945,912	232,698
Real Estate, Improvements	683,284	716,627	549,506
Real Estate, Cost of Real Estate Sold	(336,327)	(1,538,680)	(387,017)
Impairment Charges	0	(859)	(3,719)
Write Off of Fully Depreciated Assets	(38,158)	(34,052)	(50,064)
Real Estate, Gross	6,612,229	6,523,281	6,181,877	$ 7,248,346	$ 6,612,229	$ 6,523,281	$ 6,181,877
Total Land, Land Improvements, Buildings and Tenant Improvements Held-for-Sale				0	(18,662)	(1,378,476)
SEC Schedule III, Real Estate, Excluding Held-for-Sale				7,248,346	6,593,567	5,144,805
Real Estate Accumulated Depreciation				1,345,060	1,196,458	1,302,210	$ 1,199,608
Real Estate Accumulated Depreciation, Depreciation Expense	256,250	242,606	255,419
Real Estate Accumulated Depreciation, Real Estate Sold	(69,490)	(314,306)	(102,753)
Real Estate Accumulated Depreciation, Other Deductions	$ (38,158)	$ (34,052)	$ (50,064)
Schedule III - Accumulated Depreciation of Assets Held-for-Sale				(884)	(2,553)	(259,266)
Real Estate Investment Property, Accumulated Depreciation				$ 1,344,176	$ 1,193,905	$ 1,042,944