Acquisitions of Real Estate Property (Details 3) (USD $)	1 Months Ended			12 Months Ended		12 Months Ended
	May 31, 2012 property	Dec. 31, 2012	Aug. 31, 2012	Dec. 31, 2011 Other Acquisitions property	Dec. 31, 2012 Other Acquisitions	Dec. 31, 2011 Five MOBs Other Acquisitions
Business acquisition
Purchase of joint ventures		$ 1,587,068,000	$ 350,000,000	$ 329,500,000	$ 649,387,000
Assumption of debt			101,600,000	134,900,000		144,000,000
Number of Medical office buildings				14		5
Senior housing communities acquired	21			5
Acquired lease intangibles		202,799,000			71,347,000	36,600,000
Senior housing communities acquired						58
Purchase price of acquisition of assets			$ 380,000,000			$ 186,000,000
Noncontrolling interest percentage acquired, low end of range				15.00%
Noncontrolling interest percentage acquired, high end of range				25.00%