Significant Acquisitions and Dispositions Dispositions (Details) $ in Thousands, sqft in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2019 USD ($) buildings entities	Dec. 31, 2018 USD ($) buildings	Dec. 31, 2017 USD ($) sqft buildings entities	Nov. 30, 2019	Oct. 31, 2019	Aug. 31, 2019	Sep. 30, 2018
Dispositions Disclosures [Line Items]
Proceeds from Sale of Real Estate Held-for-investment		$ 432,662	$ 511,391	$ 2,523,358
Number of Real Estate Properties Sold	18	28	15	98
Debt Instrument, Interest Rate, Stated Percentage					2.88%	3.88%	3.38%	4.00%
Notes receivable from property sales		$ 110,000	$ 272,550
Proceeds from Collection of Notes Receivable		145,000
Notes receivable from buyers in property sales		$ 0	0	$ 404,846
Number of Unconsolidated Joint Ventures in which Equity Interests Held | entities		9
Equity in earnings of unconsolidated joint ventures		$ 31,406	21,444	63,310
Promote income		0	0	20,007
Income Tax Expense (Benefit), Continuing Operations, Discontinued Operations				17,700
Discontinued Operation, Tax Effect of Discontinued Operation		0	0	12,465
Income Tax Expense (Benefit)		8,686	8,828	(357)
Proceeds from Equity Method Investment, Distribution, Return of Capital		$ 26,272	$ 23,133	$ 124,956
Square Footage Of Real Estate Properties Acquired Or Disposed | sqft				3.4
London Interbank Offered Rate (LIBOR) [Member]
Dispositions Disclosures [Line Items]
Debt Instrument, Description of Variable Rate Basis		LIBOR
Medical Office Portfolio Sale [Member]
Dispositions Disclosures [Line Items]
Proceeds from Sale of Real Estate Held-for-investment				$ 2,780,000
Number of Real Estate Properties Sold | buildings				85
Gains (Losses) on Sales of Investment Real Estate				$ 1,390,000
Notes receivable from property sales				$ 400,000
Number of Unconsolidated Joint Ventures in which Equity Interests Held | entities				2
Equity in earnings of unconsolidated joint ventures				$ 47,500
Proceeds from Equity Method Investment, Distribution, Return of Capital				105,300
Continuing Operations [Member]
Dispositions Disclosures [Line Items]
Income Tax Expense (Benefit)				$ 5,200
BCC Cancer Center Venture, L.P. [Member]
Dispositions Disclosures [Line Items]
Number of Unconsolidated Joint Ventures in which Equity Interests Held | entities				1