Segment Reporting (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Summary of information for reportable segments
Rental income	$ 355,599	$ 422,628	$ 722,741	$ 838,290
Resident fees and services	677,040	615,220	1,347,377	1,217,369
Interest income	20,901	24,007	41,649	49,195
Other income	5,062	14,802	9,133	18,851
Total revenues	1,058,602	1,076,657	2,120,900	2,123,705
Property operating expenses	501,855	458,832	1,012,024	908,468
Net Operating Income from Continuing Operations	556,747	617,825	1,108,876	1,215,237
Interest expense	116,231	132,326	234,827	265,285
Loss (gain) on derivatives, net	736	0	1,960	0
Depreciation and amortization	224,847	226,569	453,124	455,265
General and administrative	32,632	39,914	63,733	85,606
Transaction costs	0	5,157	0	13,365
Loss (gain) on extinguishment of debt, net	5,515	33	36,870	9
Impairment of Asset	13,631	0	24,662	14,314
Other expenses	6,339	3,161	18,014	3,161
Income (loss) from continuing operations before income taxes and income from unconsolidated entities	156,816	210,665	275,686	378,232
Income tax expense	8,448	513	6,203	2,239
(Loss) income from unconsolidated entities	(3,978)	(1,959)	(27,084)	(5,778)
Income (loss) from continuing operations	161,286	209,219	254,805	374,693
Gain (loss) on real estate dispositions, net	42,155	1,530	286,247	1,530
Net income	203,441	$ 210,749	541,052	$ 376,223
Total assets	$ 27,975,786		$ 27,975,786		$ 28,865,184
Percent Of Assets	1		1		1
Percent Of Revenues	1	1	1	1
United States
Summary of information for reportable segments
Total revenues	$ 851,943	$ 862,115	$ 1,710,611	$ 1,704,470
Total assets	$ 22,323,973		$ 22,323,973		$ 23,572,459
Percent Of Assets	0.798		0.798		0.817
Percent Of Revenues	0.805	0.801	0.807	0.803
United Kingdom
Summary of information for reportable segments
Total revenues	$ 99,747	$ 102,593	$ 193,590	$ 203,148
Total assets	$ 3,064,196		$ 3,064,196		$ 2,782,489
Percent Of Assets	0.11		0.11		0.096
Percent Of Revenues	0.094	0.095	0.091	0.095
Canada
Summary of information for reportable segments
Total revenues	$ 106,912	$ 111,949	$ 216,699	$ 216,087
Total assets	$ 2,587,617		$ 2,587,617		$ 2,510,236
Percent Of Assets	0.092		0.092		0.087
Percent Of Revenues	0.101	0.104	0.102	0.102
Triple Net [Member]
Summary of information for reportable segments
Rental income	$ 217,889	$ 287,134	$ 445,180	$ 570,958
Resident fees and services	0	0	0	0
Interest income	20,901	21,971	41,580	44,824
Other income	2,557	1,206	4,321	2,695
Total revenues	241,347	310,311	491,081	618,477
Property operating expenses	0	0	0	0
Net Operating Income from Continuing Operations	241,347	310,311	491,081	618,477
Interest expense	2,515	5,754	8,025	12,117
Loss (gain) on derivatives, net	736		1,960	0
Depreciation and amortization	60,171	75,809	119,781	155,609
General and administrative	0	0	0	0
Transaction costs		1,291		4,143
Loss (gain) on extinguishment of debt, net	0	121	29,083	97
Impairment of Asset	4,846	0	4,846	14,314
Other expenses	2,181		7,190	0
Income (loss) from continuing operations before income taxes and income from unconsolidated entities	170,898	227,336	320,196	432,197
Income tax expense	(1,471)	(213)	(2,271)	(528)
(Loss) income from unconsolidated entities	3,867	3,018	9,505	6,100
Income (loss) from continuing operations	173,294	230,141	327,430	437,769
Gain (loss) on real estate dispositions, net	42,155	1,530	273,236	1,530
Net income	215,449	231,671	600,666	439,299
Total assets	9,990,063		9,990,063
Senior housing - operating [Member]
Summary of information for reportable segments
Rental income	0	0	0	0
Resident fees and services	677,040	615,220	1,347,377	1,217,369
Interest income	0	1,042	69	2,073
Other income	1,049	8,989	2,510	11,178
Total revenues	678,089	625,251	1,349,956	1,230,620
Property operating expenses	459,111	417,996	921,536	826,890
Net Operating Income from Continuing Operations	218,978	207,255	428,420	403,730
Interest expense	15,403	20,274	31,219	40,797
Loss (gain) on derivatives, net	0		0	0
Depreciation and amortization	117,198	102,312	236,935	204,144
General and administrative	0	0	0	0
Transaction costs		3,247		7,180
Loss (gain) on extinguishment of debt, net	2,524	(88)	3,414	(88)
Impairment of Asset	8,785	0	14,191	0
Other expenses	1,165		2,943	0
Income (loss) from continuing operations before income taxes and income from unconsolidated entities	73,903	81,510	139,718	151,697
Income tax expense	10,247	2,023	9,160	4,789
(Loss) income from unconsolidated entities	(8,449)	(4,887)	(37,640)	(11,822)
Income (loss) from continuing operations	75,701	78,646	111,238	144,664
Gain (loss) on real estate dispositions, net	0	0	13,011	0
Net income	75,701	78,646	124,249	144,664
Total assets	12,753,128		12,753,128
Outpatient Medical [Member]
Summary of information for reportable segments
Rental income	137,710	135,494	277,561	267,332
Resident fees and services	0	0	0	0
Interest income	0	994	0	2,298
Other income	1,217	4,153	1,830	4,466
Total revenues	138,927	140,641	279,391	274,096
Property operating expenses	42,744	40,836	90,488	81,578
Net Operating Income from Continuing Operations	96,183	99,805	188,903	192,518
Interest expense	2,122	5,402	4,413	11,146
Loss (gain) on derivatives, net	0		0	0
Depreciation and amortization	47,478	48,448	96,408	95,512
General and administrative	0	0	0	0
Transaction costs		619		2,042
Loss (gain) on extinguishment of debt, net	2,991	0	4,373	0
Impairment of Asset	0	0	5,625	0
Other expenses	1,310		1,671	0
Income (loss) from continuing operations before income taxes and income from unconsolidated entities	42,282	45,336	76,413	83,818
Income tax expense	(351)	(248)	(686)	(476)
(Loss) income from unconsolidated entities	604	(90)	1,051	(56)
Income (loss) from continuing operations	42,535	44,998	76,778	83,286
Gain (loss) on real estate dispositions, net	0	0	0	0
Net income	42,535	44,998	76,778	83,286
Total assets	5,008,067		5,008,067
Corporate, Non-Segment [Member]
Summary of information for reportable segments
Rental income	0	0	0	0
Resident fees and services	0	0	0	0
Interest income	0	0	0	0
Other income	239	454	472	512
Total revenues	239	454	472	512
Property operating expenses	0	0	0	0
Net Operating Income from Continuing Operations	239	454	472	512
Interest expense	96,191	100,896	191,170	201,225
Loss (gain) on derivatives, net	0		0	0
Depreciation and amortization	0	0	0	0
General and administrative	32,632	39,914	63,733	85,606
Transaction costs		0		0
Loss (gain) on extinguishment of debt, net	0	0	0	0
Impairment of Asset	0	0	0	0
Other expenses	1,683	3,161	6,210	3,161
Income (loss) from continuing operations before income taxes and income from unconsolidated entities	(130,267)	(143,517)	(260,641)	(289,480)
Income tax expense	23	(1,049)	0	(1,546)
(Loss) income from unconsolidated entities	0	0	0	0
Income (loss) from continuing operations	(130,244)	(144,566)	(260,641)	(291,026)
Gain (loss) on real estate dispositions, net	0	0	0	0
Net income	(130,244)	$ (144,566)	(260,641)	$ (291,026)
Total assets	$ 224,528		$ 224,528