Segment Reporting (Segment Information for Reportable Segments) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of information for reportable segments
Resident fees and services									$ 3,234,852,000	$ 2,779,423,000	$ 2,504,731,000
Rental income									1,380,422,000	1,445,871,000	1,648,815,000
Interest income									55,814,000	73,811,000	97,963,000
Other income									29,411,000	17,536,000	29,651,000
Total revenues	$ 1,241,243,000	$ 1,236,379,000	$ 1,125,912,000	$ 1,096,965,000	$ 1,104,257,000	$ 1,091,483,000	$ 1,058,602,000	$ 1,062,298,000	4,700,499,000	4,316,641,000	4,281,160,000
Property operating expenses									2,433,017,000	2,083,925,000	1,876,983,000
Consolidated net operating income									2,267,482,000	2,232,716,000	2,404,177,000
Depreciation and amortization									950,459,000	921,720,000	901,242,000
Interest expense									526,592,000	484,622,000	521,345,000
General and administrative expenses									126,383,000	122,008,000	155,241,000
Loss (gain) on derivatives and financial instruments, net									(4,016,000)	2,284,000	(2,448,000)
Transaction costs									0	0	42,910,000
Loss (gain) on extinguishment of debt, net									16,097,000	37,241,000	17,214,000
Provision for loan losses					62,966,000				0	62,966,000	10,215,000
Impairment of assets					99,821,100				115,579,000	124,483,000	37,207,000
Other expenses									112,898,000	177,776,000	11,998,000
Income (loss) from continuing operations before income taxes and other items									423,490,000	299,616,000	709,253,000
Income tax (expense) benefit									(8,674,000)	(20,128,000)	19,128,000
Income (loss) from unconsolidated entities									(641,000)	(83,125,000)	(10,357,000)
Gain (loss) on real estate dispositions, net									415,575,000	344,250,000	364,046,000
Income from continuing operations									829,750,000	540,613,000	1,082,070,000
Net income									829,750,000	540,613,000	1,082,070,000
Total assets	30,342,072,000				27,944,445,000				30,342,072,000	27,944,445,000
Non capitalizable transaction cost									81,116,000	88,316,000
Other than temporary asset impairment charges					18,294,000					18,294,000
Expense recognized for the donation of the corporate headquarters										40,730,000
Corporate, Non-Segment
Summary of information for reportable segments
Resident fees and services									0	0	0
Rental income									0	0	0
Interest income									0	0	0
Other income									2,275,000	1,538,000	939,000
Total revenues									2,275,000	1,538,000	939,000
Property operating expenses									0	0	0
Consolidated net operating income									2,275,000	1,538,000	939,000
Depreciation and amortization									0	0	0
Interest expense									436,256,000	396,148,000	399,035,000
General and administrative expenses									126,383,000	122,008,000	155,241,000
Loss (gain) on derivatives and financial instruments, net									0	0	(2,516,000)
Transaction costs											0
Loss (gain) on extinguishment of debt, net									4,091,000	0	16,439,000
Provision for loan losses										0	0
Impairment of assets									0	0	0
Other expenses									7,729,000	50,829,000	11,998,000
Income (loss) from continuing operations before income taxes and other items									(572,184,000)	(567,447,000)	(579,258,000)
Income tax (expense) benefit									(11,362,000)	2,070,000	24,488,000
Income (loss) from unconsolidated entities									0	0	0
Gain (loss) on real estate dispositions, net									0	0	0
Income from continuing operations									(583,546,000)	(565,377,000)	(554,770,000)
Net income									(583,546,000)	(565,377,000)	(554,770,000)
Total assets	196,908,000				104,955,000				196,908,000	104,955,000
Seniors Housing Operating | Operating Segments
Summary of information for reportable segments
Resident fees and services									3,234,852,000	2,779,423,000	2,504,731,000
Rental income									0	0	0
Interest income									578,000	69,000	4,180,000
Other income									5,024,000	5,127,000	17,085,000
Total revenues									3,240,454,000	2,784,619,000	2,525,996,000
Property operating expenses									2,255,432,000	1,904,593,000	1,711,882,000
Consolidated net operating income									985,022,000	880,026,000	814,114,000
Depreciation and amortization									529,449,000	484,796,000	415,429,000
Interest expense									69,060,000	63,265,000	81,853,000
General and administrative expenses									0	0	0
Loss (gain) on derivatives and financial instruments, net									0	0	0
Transaction costs											29,207,000
Loss (gain) on extinguishment of debt, net									110,000	3,785,000	(88,000)
Provision for loan losses										0	0
Impairment of assets									7,599,000	21,949,000	12,403,000
Other expenses									6,624,000	8,347,000	0
Income (loss) from continuing operations before income taxes and other items									372,180,000	297,884,000	275,310,000
Income tax (expense) benefit									1,202,000	(16,430,000)	(3,762,000)
Income (loss) from unconsolidated entities									(28,142,000)	(105,236,000)	(20,442,000)
Gain (loss) on real estate dispositions, net									(2,245,000)	56,295,000	9,880,000
Income from continuing operations									342,995,000	232,513,000	260,986,000
Net income									342,995,000	232,513,000	260,986,000
Total assets	14,607,127,000				13,432,001,000				14,607,127,000	13,432,001,000
Triple-net | Operating Segments
Summary of information for reportable segments
Resident fees and services									0	0	0
Rental income									828,865,000	885,811,000	1,112,325,000
Interest income									54,926,000	73,742,000	90,476,000
Other income									17,173,000	7,531,000	6,059,000
Total revenues									900,964,000	967,084,000	1,208,860,000
Property operating expenses									915,000	0	0
Consolidated net operating income									900,049,000	967,084,000	1,208,860,000
Depreciation and amortization									235,480,000	243,830,000	297,197,000
Interest expense									14,225,000	15,194,000	21,370,000
General and administrative expenses									0	0	0
Loss (gain) on derivatives and financial instruments, net									(4,016,000)	2,284,000	68,000
Transaction costs											10,016,000
Loss (gain) on extinguishment of debt, net									(32,000)	29,083,000	863,000
Provision for loan losses										62,966,000	6,935,000
Impairment of assets									107,980,000	96,909,000	20,169,000
Other expenses									90,975,000	116,689,000	0
Income (loss) from continuing operations before income taxes and other items									455,437,000	400,129,000	852,242,000
Income tax (expense) benefit									1,611,000	(4,291,000)	(1,087,000)
Income (loss) from unconsolidated entities									21,938,000	19,428,000	9,767,000
Gain (loss) on real estate dispositions, net									196,589,000	286,325,000	355,394,000
Income from continuing operations									675,575,000	701,591,000	1,216,316,000
Net income									675,575,000	701,591,000	1,216,316,000
Total assets	10,111,227,000				9,325,344,000				10,111,227,000	9,325,344,000
Outpatient Medical | Operating Segments
Summary of information for reportable segments
Resident fees and services									0	0	0
Rental income									551,557,000	560,060,000	536,490,000
Interest income									310,000	0	3,307,000
Other income									4,939,000	3,340,000	5,568,000
Total revenues									556,806,000	563,400,000	545,365,000
Property operating expenses									176,670,000	179,332,000	165,101,000
Consolidated net operating income									380,136,000	384,068,000	380,264,000
Depreciation and amortization									185,530,000	193,094,000	188,616,000
Interest expense									7,051,000	10,015,000	19,087,000
General and administrative expenses									0	0	0
Loss (gain) on derivatives and financial instruments, net									0	0	0
Transaction costs											3,687,000
Loss (gain) on extinguishment of debt, net									11,928,000	4,373,000	0
Provision for loan losses										0	3,280,000
Impairment of assets									0	5,625,000	4,635,000
Other expenses									7,570,000	1,911,000	0
Income (loss) from continuing operations before income taxes and other items									168,057,000	169,050,000	160,959,000
Income tax (expense) benefit									(125,000)	(1,477,000)	(511,000)
Income (loss) from unconsolidated entities									5,563,000	2,683,000	318,000
Gain (loss) on real estate dispositions, net									221,231,000	1,630,000	(1,228,000)
Income from continuing operations									394,726,000	171,886,000	159,538,000
Net income									394,726,000	171,886,000	$ 159,538,000
Total assets	$ 5,426,810,000				$ 5,082,145,000				$ 5,426,810,000	$ 5,082,145,000