SEGMENT INFORMATION - Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total assets	$ 24,275,162	$ 21,226,171
Percentage of total assets	100.00%	100.00%
Triple-Net Leased Properties
Segment Reporting Information [Line Items]
Total assets	$ 9,638,035	$ 9,176,159
Percentage of total assets	39.70%	43.20%
Senior Living Operations
Segment Reporting Information [Line Items]
Total assets	$ 8,267,934	$ 7,421,924
Percentage of total assets	34.00%	35.00%
MOB Operations
Segment Reporting Information [Line Items]
Total assets	$ 5,233,638	$ 3,526,217
Percentage of total assets	21.60%	16.60%
All Other
Segment Reporting Information [Line Items]
Total assets	$ 1,135,555	$ 1,101,871
Percentage of total assets	4.70%	5.20%