Dispositions, Assets Held for Sale and Discontinued Operations (Details) - USD ($)		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014
Real property dispositions:
Total dispositions		$ 418,759,000	$ 400,050,000
Net loss (gain) on sales of properties		(249,002,000)	(42,683,000)
Proceeds from sales of real property		667,761,000	442,733,000
Triple Net [Member]
Real property dispositions:
Total dispositions		246,116,000	56,713,000
Outpatient Medical [Member]
Real property dispositions:
Total dispositions	[1]	166,919,000	343,337,000
Land parcels [Member]
Real property dispositions:
Total dispositions		$ 5,724,000	$ 0

[1] (1) Dispositions occurring in the nine-month period ending September 30, 2015 primarily related to the disposition of an unconsolidated equity investment with Forest City Enterprises.