Dispositions, Assets Held for Sale and Discontinued Operations (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Real property dispositions:
Total dispositions	$ 0	$ 212,115,000
Gain (loss) on sales of properties, net	0	82,492,000
Noncash disposition activity	0	0
Proceeds from sales of real property	0	294,607,000
Seniors Housing Facilities Triple Net [Member]
Real property dispositions:
Total dispositions	0	76,331,000
Medical facilities [Member]
Real property dispositions:
Total dispositions	$ 0	$ 135,784,000