SEGMENT INFORMATION - Income Statement (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) segment	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Segment Reporting [Abstract]
Number of reportable business segments | segment			3
Revenues:
Rental income	$ 343,783	$ 287,559	$ 991,878	$ 846,989
Resident fees and services	454,825	396,247	1,356,384	1,141,781
Medical office building and other services revenue	10,000	7,573	29,951	18,240
Income from loans and investments	18,924	13,186	66,192	36,902
Interest and other income	74	367	719	811
Total revenues	827,606	704,932	2,445,124	2,044,723
Less:
Interest and other income	74	367	719	811
Property-level operating expenses	347,845	306,536	1,031,306	883,014
Medical office building services costs	6,416	4,568	19,098	9,565
Segment NOI	473,271	393,461	1,394,001	1,151,333
Income (loss) from unconsolidated entities	(955)	(47)	(1,197)	549
Segment profit	472,316	393,414	1,392,804	1,151,882
Interest and other income	74	367	719	811
Interest expense	(97,135)	(77,325)	(263,422)	(214,117)
Depreciation and amortization	(226,332)	(173,006)	(657,262)	(507,167)
General, administrative and professional fees	(32,114)	(29,464)	(100,399)	(93,632)
Loss on extinguishment of debt, net	(15,331)	(2,414)	(14,897)	(5,079)
Merger-related expenses and deal costs	(62,145)	(16,188)	(105,023)	(35,944)
Other	(4,795)	(9,413)	(13,948)	(18,070)
Income tax benefit (expense)	10,697	1,887	27,736	(4,820)
Discontinued operations	(22,383)	18,171	13,434	79,026
Gain on real estate dispositions	265	3,625	14,420	16,514
Net income	23,117	109,654	294,162	369,404	$ 477,186
Triple-Net Leased Properties
Revenues:
Rental income	201,028	170,873	571,591	500,047
Resident fees and services	0	0	0	0
Medical office building and other services revenue	1,011	1,136	3,286	3,429
Income from loans and investments	0	0	0	0
Interest and other income	0	0	0	0
Total revenues	202,039	172,009	574,877	503,476
Less:
Interest and other income	0	0	0	0
Property-level operating expenses	0	0	0	0
Medical office building services costs	0	0	0	0
Segment NOI	202,039	172,009	574,877	503,476
Income (loss) from unconsolidated entities	(1,431)	252	(785)	838
Segment profit	200,608	172,261	574,092	504,314
Interest and other income	0	0	0	0
Senior Living Operations
Revenues:
Rental income	0	0	0	0
Resident fees and services	454,825	396,247	1,356,384	1,141,781
Medical office building and other services revenue	0	0	0	0
Income from loans and investments	0	0	0	0
Interest and other income	0	0	0	0
Total revenues	454,825	396,247	1,356,384	1,141,781
Less:
Interest and other income	0	0	0	0
Property-level operating expenses	304,540	265,274	902,154	762,993
Medical office building services costs	0	0	0	0
Segment NOI	150,285	130,973	454,230	378,788
Income (loss) from unconsolidated entities	433	(225)	(221)	(209)
Segment profit	150,718	130,748	454,009	378,579
Interest and other income	0	0	0	0
MOB Operations
Revenues:
Rental income	142,755	116,686	420,287	346,942
Resident fees and services	0	0	0	0
Medical office building and other services revenue	8,459	5,937	25,066	13,311
Income from loans and investments	0	0	0	0
Interest and other income	0	0	0	0
Total revenues	151,214	122,623	445,353	360,253
Less:
Interest and other income	0	0	0	0
Property-level operating expenses	43,305	41,262	129,152	120,021
Medical office building services costs	6,416	4,568	19,098	9,565
Segment NOI	101,493	76,793	297,103	230,667
Income (loss) from unconsolidated entities	108	66	226	326
Segment profit	101,601	76,859	297,329	230,993
Interest and other income	0	0	0	0
All Other
Revenues:
Rental income	0	0	0	0
Resident fees and services	0	0	0	0
Medical office building and other services revenue	530	500	1,599	1,500
Income from loans and investments	18,924	13,186	66,192	36,902
Interest and other income	74	367	719	811
Total revenues	19,528	14,053	68,510	39,213
Less:
Interest and other income	74	367	719	811
Property-level operating expenses	0	0	0	0
Medical office building services costs	0	0	0	0
Segment NOI	19,454	13,686	67,791	38,402
Income (loss) from unconsolidated entities	(65)	(140)	(417)	(406)
Segment profit	19,389	13,546	67,374	37,996
Interest and other income	$ 74	$ 367	$ 719	$ 811