Acquisitions and Dispositions Dispositions (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) buildings entities	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) buildings entities	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Dispositions Disclosures [Line Items]
Number of Unconsolidated Joint Ventures in which Equity Interests Held | entities	1		1
Equity in earnings of unconsolidated companies	$ 1,841	$ 12,010	$ 58,523	$ 37,404
Proceeds from Sale of Real Estate Held-for-investment			$ 2,282,419	369,118
Total Properties Sold or Classified as Held for Sale | buildings			129
Promote income	0	2,212	$ 20,007	26,299
Income Tax Expense (Benefit), Continuing Operations, Discontinued Operations			19,100
Income Tax Expense (Benefit)	359	(359)	7,918	(173)
Income tax (expense) benefit	(876)	$ 0	10,736	0
Financing Receivable, Net	$ 426,678		426,678		$ 25,460
Capital distributions from unconsolidated companies			111,635	$ 52,514
Continuing Operations [Member]
Dispositions Disclosures [Line Items]
Income Tax Expense (Benefit)			$ 8,400
Medical Office Portfolio Sale [Member]
Dispositions Disclosures [Line Items]
Number of Unconsolidated Joint Ventures in which Equity Interests Held | entities	2		2
Equity in earnings of unconsolidated companies			$ 47,500
Proceeds from Sale of Real Estate Held-for-investment	$ 250,000		$ 2,600,000
Total Properties Sold or Classified as Held for Sale | buildings	7		84
Gains (Losses) on Sales of Investment Real Estate	$ 120,400		$ 1,260,000
Financing Receivable, Net	$ 400,000		$ 400,000
Debt Instrument, Interest Rate, Stated Percentage	4.00%		4.00%
Capital distributions from unconsolidated companies			$ 105,300