SEGMENT INFORMATION - Income Statement (Details) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) segment	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Segment Reporting [Abstract]
Number of reportable business segments | segment			3
Revenues:
Rental income	$ 400,965	$ 357,616	$ 804,161	$ 710,685
Resident fees and services	454,645	374,473	901,559	745,534
Medical office building and other services revenue	9,408	4,367	19,951	10,667
Income from loans and investments	26,068	14,625	48,967	25,392
Interest and other income	236	173	708	446
Total revenues	891,322	751,254	1,775,346	1,492,724
Less:
Interest and other income	236	173	708	446
Property-level operating expenses	342,573	288,759	683,284	576,399
Medical office building services costs	5,764	1,626	12,682	4,997
Segment NOI	542,749	460,696	1,078,672	910,882
Income (loss) from unconsolidated entities	9	348	(242)	596
Segment profit	542,758	461,044	1,078,430	911,478
Interest and other income	236	173	708	446
Interest expense	(107,591)	(91,501)	(214,181)	(179,342)
Depreciation and amortization	(249,195)	(190,818)	(496,636)	(384,412)
General, administrative and professional fees	(33,962)	(31,306)	(68,292)	(64,172)
Gain (loss) on extinguishment of debt	455	(2,924)	434	(2,665)
Merger-related expenses and deal costs	(14,585)	(9,599)	(49,757)	(20,359)
Other	(5,091)	(4,863)	(10,387)	(10,092)
Income tax benefit (expense)	9,789	(3,274)	17,039	(6,707)
Discontinued operations	67	(255)	(356)	2,776
Gain on real estate dispositions	7,469	11,889	14,155	12,889
Net income	150,350	138,566	271,157	259,840	$ 477,186
Triple-Net Leased Properties
Revenues:
Rental income	260,562	242,726	526,768	480,572
Resident fees and services	0	0	0	0
Medical office building and other services revenue	1,139	1,145	2,275	2,293
Income from loans and investments	0	0	0	0
Interest and other income	0	0	0	0
Total revenues	261,701	243,871	529,043	482,865
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	261,701	243,871	529,043	482,865
Income (loss) from unconsolidated entities	221	17	645	586
Segment profit	261,922	243,888	529,688	483,451
Interest and other income	0	0	0	0
Senior Living Operations
Revenues:
Rental income	0	0	0	0
Resident fees and services	454,645	374,473	901,559	745,534
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	454,645	374,473	901,559	745,534
Less:
Interest and other income	0	0	0	0
Property-level operating expenses	299,252	249,424	597,614	497,719
Medical office building services costs	0	0	0	0
Segment NOI	155,393	125,049	303,945	247,815
Income (loss) from unconsolidated entities	(240)	160	(662)	16
Segment profit	155,153	125,209	303,283	247,831
Interest and other income	0	0	0	0
MOB Operations
Revenues:
Rental income	140,403	114,890	277,393	230,113
Resident fees and services	0	0	0	0
Medical office building and other services revenue	7,749	2,722	16,607	7,374
Income from loans and investments	0	0	0	0
Interest and other income	0	0	0	0
Total revenues	148,152	117,612	294,000	237,487
Less:
Interest and other income	0	0	0	0
Property-level operating expenses	43,321	39,335	85,670	78,680
Medical office building services costs	5,764	1,626	12,682	4,997
Segment NOI	99,067	76,651	195,648	153,810
Income (loss) from unconsolidated entities	143	307	119	260
Segment profit	99,210	76,958	195,767	154,070
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	520	500	1,069	1,000
Income from loans and investments	26,068	14,625	48,967	25,392
Interest and other income	236	173	708	446
Total revenues	26,824	15,298	50,744	26,838
Less:
Interest and other income	236	173	708	446
Property-level operating expenses	0	0	0	0
Medical office building services costs	0	0	0	0
Segment NOI	26,588	15,125	50,036	26,392
Income (loss) from unconsolidated entities	(115)	(136)	(344)	(266)
Segment profit	26,473	14,989	49,692	26,126
Interest and other income	$ 236	$ 173	$ 708	$ 446