ACQUISITIONS OF REAL ESTATE PROPERTY (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	1 Months Ended	3 Months Ended		9 Months Ended					9 Months Ended		9 Months Ended			9 Months Ended		9 Months Ended				9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended							1 Months Ended	9 Months Ended	1 Months Ended		12 Months Ended
	Apr. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Sep. 30, 2013 2013 Acquisitions	Sep. 30, 2013 2013 Acquisitions Triple-Net Leased Properties	Sep. 30, 2013 2013 Acquisitions Triple-Net Leased Properties Seniors Housing Communities property	Sep. 30, 2013 2013 Acquisitions Triple-Net Leased Properties Seniors Housing Communities Corporate Joint Venture property	Sep. 30, 2013 2013 Acquisitions Senior Living Operations	Sep. 30, 2013 2013 Acquisitions Senior Living Operations Seniors Housing Communities property	Sep. 30, 2013 2013 Acquisitions MOB Operations	Sep. 30, 2013 2013 Acquisitions MOB Operations Medical Office Buildings property	Sep. 30, 2013 2013 Acquisitions MOB Operations Medical Office Buildings Equity Method Investee property	Sep. 30, 2013 Developement Projects	Dec. 31, 2012 Developement Projects	Sep. 30, 2013 Developement Projects Seniors Housing Communities property	Dec. 31, 2012 Developement Projects Seniors Housing Communities property	Sep. 30, 2013 Developement Projects Medical Office Buildings property	Dec. 31, 2012 Developement Projects Medical Office Buildings property	Sep. 30, 2013 Developement Projects Hospitals property	Dec. 31, 2012 2012 Acquisitions	Dec. 31, 2012 2012 Acquisitions Triple-Net Leased Properties	Dec. 31, 2012 2012 Acquisitions Senior Living Operations	Dec. 31, 2012 2012 Acquisitions MOB Operations	Dec. 31, 2012 ATRIA	Dec. 31, 2012 Funds Previously Managed by LFREI	Apr. 30, 2012 Cogdell Spencer Inc	Dec. 31, 2012 Cogdell Spencer Inc	Apr. 30, 2012 Cogdell Spencer Inc Medical Office Buildings property	May 31, 2012 SUNRISE Seniors Housing Communities property	Dec. 31, 2012 Other Acquisitions Seniors Housing Communities property	Dec. 31, 2012 Other Acquisitions Skilled Nursing Facilities property	Dec. 31, 2012 Other Acquisitions Medical Office Buildings property	Dec. 31, 2012 Other Acquisitions Medical Office Buildings Unconsolidated Properties property
Business Acquisition [Line Items]
Ownership interests accounted for under the equity method (as a percent)						5.00%																							34.00%
Treasury stock, shares		3,699		3,699				3,699																						3,700
Extinguished performance-based payment																														$ 44,000,000
Number of real estate properties acquired											27	1		22		10	2																71	16	21	2	44	36
Number of real estate properties acquired, managed by property management business																																	44
Number of real estate properties acquired, previously capital leases														8
Business combination, consideration transferred											860,000,000			700,000,000		150,000,000															760,000,000
Business combination, joint venture partners' share of net debt assumed																															36,300,000
Business combination, right to receive cash, per share of common stock outstanding (in dollars per share)	$ 4.25
Preferred stock, dividend rate, percentage	8.50%
Business combination, consideration transferred per share of preferred stock (in dollars per share)	$ 25.00
Business combination, notes payable and other debt assumed									41,436,000	36,300,000			5,136,000		0										412,825,000	57,219,000	0	355,606,000			203,800,000
Number of real estate properties completed																				2	2	1	3	1
Net real estate property		18,174,943,000		18,174,943,000			17,111,532,000											65,200,000	116,900,000
Settlement of capital lease obligation				142,400,000
Business acquisition, transaction costs									11,300,000																							28,600,000
Merger-related expenses and deal costs		$ 6,208,000	$ 4,917,000	$ 17,137,000	$ 49,566,000				$ 10,400,000																							$ 28,600,000