SEGMENT INFORMATION - Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total assets	$ 22,413,977	$ 21,165,913
Percentage of total assets	100.00%	100.00%
Triple-Net Leased Properties
Segment Reporting Information [Line Items]
Total assets	$ 8,143,204	$ 9,173,873
Percentage of total assets	36.30%	43.30%
Senior Living Operations
Segment Reporting Information [Line Items]
Total assets	$ 8,154,058	$ 7,416,150
Percentage of total assets	36.40%	35.00%
MOB Operations
Segment Reporting Information [Line Items]
Total assets	$ 5,179,767	$ 3,525,397
Percentage of total assets	23.10%	16.70%
All Other
Segment Reporting Information [Line Items]
Total assets	$ 936,948	$ 1,050,493
Percentage of total assets	4.20%	5.00%