ACQUISITIONS OF REAL ESTATE PROPERTY (Details) (USD $)	3 Months Ended		9 Months Ended		0 Months Ended		1 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 property	Sep. 30, 2011	Apr. 02, 2012 Cogdell Acquisition property	Sep. 30, 2012 Cogdell Acquisition	May 31, 2012 Sunrise Acquisition property	Aug. 31, 2012 Other Acquisitions property	Sep. 30, 2012 Other Acquisitions property community	Dec. 31, 2011 Other Acquisitions
Business acquisition
Number of MOBs in which ownership interest acquired			37		71			36	1
Number of MOBs managed by property management business of acquiree					44
Purchase price of acquired asset					$ 760,000,000		$ 362,000,000		$ 525,000,000	$ 329,500,000
Joint venture partners' share of total debt					36,300,000
Right to receive cash per share on each outstanding share of common stock outstanding					$ 4.25
Right to receive cash per share on each outstanding unit of limited partnership interest outstanding					$ 4.25
Preferred stock, Dividend rate (as a percent)					8.50%
Right to receive cash per share on each outstanding share 8.500% Series A Cumulative Redeemable Perpetual Preferred Stock					$ 25.00
Mortgage Debt assumed					203,800,000
Senior housing communities acquired							16
Senior housing communities acquired									7
Number of properties acquired									2
Fair values of the assets acquired and liabilities assumed at the date of acquisition
Land and improvements					93,585,000
Buildings and improvements					626,184,000
Construction in progress					24,117,000
Acquired lease intangibles					117,132,000
Other assets					24,459,000
Total assets acquired					885,477,000
Notes payable and other debt					213,430,000				136,400,000	134,900,000
Other liabilities					50,841,000
Total liabilities assumed					264,271,000
Noncontrolling interest assumed					29,545,000
Net assets acquired					591,661,000
Cash acquired					12,202,000
Total cash used					579,459,000
Total acquisition-related cost						28,500,000
Acquisition-related costs	$ 4,917,000	$ 69,350,000	$ 49,566,000	$ 131,606,000