ACQUISITIONS OF REAL ESTATE PROPERTY (Details) (USD $)	3 Months Ended		6 Months Ended		1 Months Ended	3 Months Ended	6 Months Ended		1 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Apr. 30, 2012 Cogdell Acquisition property	Jun. 30, 2012 Cogdell Acquisition	Jun. 30, 2012 Cogdell Acquisition	Apr. 02, 2012 Cogdell Acquisition	May 31, 2012 Sunrise Acquisition property	Jun. 30, 2012 Other Acquisitions property community	Dec. 31, 2011 Other Acquisitions
Business acquisition
Number of MOBs in which ownership interest acquired					71					1
Number of MOBs to be developed					1
Number of hospitals to be developed					1
Number of MOBs managed by property management business of acquiree					44
Purchase price of acquired asset								$ 760,000,000	$ 362,000,000	$ 155,000,000	$ 329,500,000
Number of MOBs which is still being developed					1
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
Assumption of debt										34,800,000	134,900,000
Senior housing communities acquired										8
Fair values of the assets acquired and liabilities assumed at the date of acquisition
Land and improvements								93,235,000
Buildings and improvements								615,488,000
Construction in progress								24,117,000
Acquired lease intangibles								117,088,000
Other assets								24,241,000
Total assets acquired								874,169,000
Notes payable and other debt								203,800,000
Other liabilities								40,795,000
Total liabilities assumed								254,225,000
Noncontrolling interest assumed								28,283,000
Net assets acquired								591,661,000
Cash acquired								12,202,000
Total cash used								579,459,000
Total acquisition-related cost						30,600,000	30,600,000
Acquisition-related costs	$ 36,668,000	$ 55,807,000	$ 44,649,000	$ 62,256,000		$ 27,400,000	$ 29,400,000