Dispositions, Assets Held for Sale and Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Real property dispositions:
Total dispositions	$ 212,115	$ 31,815
Gain (loss) on sales of properties, net	82,492	769
Proceeds from sales of real property	294,607	32,584
Revenues:
Rental income	2,597	23,354
Expenses:
Interest expense	445	4,908
Property operating expenses	334	893
Provision for depreciation	23	6,515
Income (loss) from discontinued operations, net	1,795	11,038
Seniors Housing Facilities Triple Net [Member]
Real property dispositions:
Total dispositions	76,331	0
Medical facilities [Member]
Real property dispositions:
Total dispositions	$ 135,784	$ 31,815