ACQUISITIONS OF REAL ESTATE PROPERTY - Fair Value of the Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
2015 Acquisitions
Business Acquisition [Line Items]
Land and improvements	$ 366,242
Buildings and improvements	2,455,917
Acquired lease intangibles	285,596
Other assets	820,212
Total assets acquired	3,927,967
Notes payable and other debt	177,857
Other liabilities	128,923
Total liabilities assumed	306,780
Net assets acquired	3,621,187
Redeemable OP unitholder interests assumed	87,245
Cash acquired	54,778
Equity issued	2,216,355
Total cash used	1,262,809
Goodwill	752,100
2015 Acquisitions | Triple-Net Leased Properties
Business Acquisition [Line Items]
Land and improvements	123,879
Buildings and improvements	627,111
Acquired lease intangibles	23,564
Other assets	143,372
Total assets acquired	917,926
Notes payable and other debt	0
Other liabilities	34,992
Total liabilities assumed	34,992
Net assets acquired	882,934
Goodwill	133,600
2015 Acquisitions | Senior Living Operations
Business Acquisition [Line Items]
Land and improvements	70,713
Buildings and improvements	703,080
Acquired lease intangibles	83,867
Other assets	275,139
Total assets acquired	1,132,799
Notes payable and other debt	77,940
Other liabilities	45,142
Total liabilities assumed	123,082
Net assets acquired	1,009,717
Goodwill	221,300
2015 Acquisitions | MOB Operations
Business Acquisition [Line Items]
Land and improvements	171,650
Buildings and improvements	1,125,726
Acquired lease intangibles	178,165
Other assets	401,701
Total assets acquired	1,877,242
Notes payable and other debt	99,917
Other liabilities	48,789
Total liabilities assumed	148,706
Net assets acquired	1,728,536
Goodwill	$ 397,200
2014 Acquisitions
Business Acquisition [Line Items]
Land and improvements		$ 145,867
Buildings and improvements		1,628,233
Acquired lease intangibles		65,335
Other assets		12,620
Total assets acquired		1,852,055
Notes payable and other debt		241,077
Other liabilities		133,323
Total liabilities assumed		374,400
Net assets acquired		1,477,655
Cash acquired		8,931
Total cash used		1,468,724
2014 Acquisitions | Triple-Net Leased Properties
Business Acquisition [Line Items]
Land and improvements		45,586
Buildings and improvements		546,849
Acquired lease intangibles		28,883
Other assets		227
Total assets acquired		621,545
Notes payable and other debt		12,927
Other liabilities		8,609
Total liabilities assumed		21,536
Net assets acquired		600,009
Cash acquired		227
Total cash used		599,782
2014 Acquisitions | Senior Living Operations
Business Acquisition [Line Items]
Land and improvements		100,281
Buildings and improvements		1,081,384
Acquired lease intangibles		36,452
Other assets		12,393
Total assets acquired		1,230,510
Notes payable and other debt		228,150
Other liabilities		124,714
Total liabilities assumed		352,864
Net assets acquired		877,646
Cash acquired		8,704
Total cash used		$ 868,942