SEGMENT INFORMATION - Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Rental income	$ 384,809	$ 395,222
Resident fees and services	514,753	464,188
Office building and other services revenue	3,328	3,406
Income from loans and investments	31,181	20,146
Interest and other income	9,634	481
Total revenues	943,705	883,443
Less:
Interest and other income	9,634	481
Property-level operating expenses	412,913	368,987
Office building services costs	115	738
Segment NOI	521,043	513,237
Loss (income) from unconsolidated entities	(40,739)	3,150
Segment profit	480,304	516,387
Interest and other income	9,634	481
Interest expense	(111,363)	(108,804)
Depreciation and amortization	(233,150)	(217,783)
General, administrative and professional fees	(37,174)	(33,961)
Loss on extinguishment of debt, net	(10,977)	(309)
Merger-related expenses and deal costs	(17,336)	(2,056)
Other	(3,120)	(1,188)
Income tax benefit	3,242	3,145
Income from continuing operations	80,060	155,912
Operating Segments | Triple-Net Leased Properties
Revenues:
Rental income	190,641	209,327
Resident fees and services	0	0
Office building and other services revenue	1,142	1,205
Income from loans and investments	0	0
Interest and other income	0	0
Total revenues	191,783	210,532
Less:
Interest and other income	0	0
Property-level operating expenses	0	0
Office building services costs	0	0
Segment NOI	191,783	210,532
Loss (income) from unconsolidated entities	(38,654)	3,269
Segment profit	153,129	213,801
Interest and other income	0	0
Operating Segments | Senior Living Operations
Revenues:
Rental income	0	0
Resident fees and services	514,753	464,188
Office building and other services revenue	0	0
Income from loans and investments	0	0
Interest and other income	0	0
Total revenues	514,753	464,188
Less:
Interest and other income	0	0
Property-level operating expenses	352,220	312,073
Office building services costs	0	0
Segment NOI	162,533	152,115
Loss (income) from unconsolidated entities	(641)	(76)
Segment profit	161,892	152,039
Interest and other income	0	0
Operating Segments | Office Operations
Revenues:
Rental income	194,168	185,895
Resident fees and services	0	0
Office building and other services revenue	1,634	1,931
Income from loans and investments	0	0
Interest and other income	0	0
Total revenues	195,802	187,826
Less:
Interest and other income	0	0
Property-level operating expenses	60,693	56,914
Office building services costs	115	738
Segment NOI	134,994	130,174
Loss (income) from unconsolidated entities	(620)	335
Segment profit	134,374	130,509
Interest and other income	0	0
All Other
Revenues:
Rental income	0	0
Resident fees and services	0	0
Office building and other services revenue	552	270
Income from loans and investments	31,181	20,146
Interest and other income	9,634	481
Total revenues	41,367	20,897
Less:
Interest and other income	9,634	481
Property-level operating expenses	0	0
Office building services costs	0	0
Segment NOI	31,733	20,416
Loss (income) from unconsolidated entities	(824)	(378)
Segment profit	30,909	20,038
Interest and other income	$ 9,634	$ 481