Segment Reporting - Summary Information for Reportable Segments (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) segment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment				3
Segment Reporting Information [Line Items]
Rental income		$ 357,984	$ 275,046	$ 1,015,550	$ 1,061,311
Total revenues		1,239,797	1,036,874	3,432,851	3,483,951
Property operating expenses		729,400	634,717	1,989,383	1,977,262
Consolidated net operating income		510,397	402,157	1,443,468	1,506,689
Depreciation and amortization		267,754	255,532	753,065	795,704
Interest expense		122,522	124,851	368,005	393,215
General and administrative expenses		32,256	31,003	93,618	100,546
Loss (gain) on derivatives and financial instruments, net		(8,078)	1,395	(6,503)	10,480
Provision for loan losses, net	$ 6,898	(271)	2,857	7,309	11,351
Impairment of assets		1,490	23,313	48,750	126,291
Other expenses		3,575	11,544	26,256	37,247
Income (loss) from continuing operations before income taxes and other items		91,154	(81,342)	102,004	(1,398)
Income tax (expense) benefit		(4,940)	(2,003)	(6,662)	(9,678)
Income (loss) from unconsolidated entities		(15,832)	(5,981)	(10,759)	(8,341)
Gain (loss) on real estate dispositions, net		119,954	484,304	223,702	902,991
Income (loss) from continuing operations		190,336	394,978	308,285	883,574
Net income (loss)		190,336	394,978	308,285	883,574
Total assets		33,480,025		33,480,025		$ 32,483,642
Loss (gain) on extinguishment of debt, net		(5)	33,004	50,964	33,253
Straight Line Rent				9,607	(66,874)
Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		835,617	740,956	2,299,972	2,360,488
Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		39,864	16,750	97,891	48,060
Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		6,332	4,122	19,438	14,092
Operating Segments | Seniors Housing Operating
Segment Reporting Information [Line Items]
Rental income		0	0	0	0
Total revenues		839,519	742,065	2,308,470	2,366,843
Property operating expenses		666,610	567,704	1,804,939	1,771,088
Consolidated net operating income		172,909	174,361	503,531	595,755
Depreciation and amortization		157,176	133,224	420,797	419,161
Interest expense		9,360	12,728	31,331	43,191
General and administrative expenses		0	0	0	0
Loss (gain) on derivatives and financial instruments, net		0	0	0	0
Provision for loan losses, net		152	86	222	86
Impairment of assets		0	12,778	22,317	91,424
Other expenses		5,449	6,488	12,617	13,463
Income (loss) from continuing operations before income taxes and other items		772	9,057	17,784	28,922
Income tax (expense) benefit		0	0	0	0
Income (loss) from unconsolidated entities		(15,810)	(7,678)	(23,514)	(25,489)
Gain (loss) on real estate dispositions, net		(615)	313,319	4,552	327,635
Income (loss) from continuing operations		(15,653)	314,698	(1,178)	331,068
Net income (loss)		(15,653)	314,698	(1,178)	331,068
Total assets		17,741,955		17,741,955
Loss (gain) on extinguishment of debt, net		0	0	(1,537)	(492)
Operating Segments | Seniors Housing Operating | Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		835,617	740,956	2,299,972	2,360,488
Operating Segments | Seniors Housing Operating | Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		1,135	113	3,110	305
Operating Segments | Seniors Housing Operating | Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		2,767	996	5,388	6,050
Operating Segments | Triple-net
Segment Reporting Information [Line Items]
Rental income		200,641	103,938	557,829	512,815
Total revenues		239,985	120,928	647,408	562,276
Property operating expenses		11,664	12,567	37,132	39,432
Consolidated net operating income		228,321	108,361	610,276	522,844
Depreciation and amortization		54,226	58,157	165,299	173,989
Interest expense		1,548	2,070	5,134	7,668
General and administrative expenses		0	0	0	0
Loss (gain) on derivatives and financial instruments, net		(8,078)	1,395	(6,503)	10,480
Provision for loan losses, net		(323)	372	10,549	8,895
Impairment of assets		1,490	10,535	24,222	34,867
Other expenses		(4,248)	2,805	4,845	6,818
Income (loss) from continuing operations before income taxes and other items		183,706	33,027	406,730	280,127
Income tax (expense) benefit		0	0	0	0
Income (loss) from unconsolidated entities		5,038	(423)	14,822	11,776
Gain (loss) on real estate dispositions, net		81,712	(619)	126,463	51,166
Income (loss) from continuing operations		270,456	31,985	548,015	343,069
Net income (loss)		270,456	31,985	548,015	343,069
Total assets		9,317,352		9,317,352
Loss (gain) on extinguishment of debt, net		0	0	0	0
Operating Segments | Triple-net | Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		0	0	0	0
Operating Segments | Triple-net | Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		38,257	15,877	86,040	46,068
Operating Segments | Triple-net | Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		1,087	1,113	3,539	3,393
Operating Segments | Outpatient Medical
Segment Reporting Information [Line Items]
Rental income		157,343	171,108	457,721	548,496
Total revenues		159,503	172,704	474,798	552,864
Property operating expenses		48,072	52,728	140,430	165,024
Consolidated net operating income		111,431	119,976	334,368	387,840
Depreciation and amortization		56,352	64,151	166,969	202,554
Interest expense		4,811	4,287	12,733	13,421
General and administrative expenses		0	0	0	0
Loss (gain) on derivatives and financial instruments, net		0	0	0	0
Provision for loan losses, net		(100)	2,399	(3,462)	2,370
Impairment of assets		0	0	2,211	0
Other expenses		640	781	2,450	8,244
Income (loss) from continuing operations before income taxes and other items		49,733	48,358	153,472	160,510
Income tax (expense) benefit		0	0	0	0
Income (loss) from unconsolidated entities		(5,060)	2,120	(2,067)	5,372
Gain (loss) on real estate dispositions, net		38,857	171,604	92,687	524,190
Income (loss) from continuing operations		83,530	222,082	244,092	690,072
Net income (loss)		83,530	222,082	244,092	690,072
Total assets		6,247,215		6,247,215
Loss (gain) on extinguishment of debt, net		(5)	0	(5)	741
Operating Segments | Outpatient Medical | Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		0	0	0	0
Operating Segments | Outpatient Medical | Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		472	760	8,741	1,687
Operating Segments | Outpatient Medical | Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		1,688	836	8,336	2,681
Non-segment / Corporate
Segment Reporting Information [Line Items]
Rental income		0	0	0	0
Total revenues		790	1,177	2,175	1,968
Property operating expenses		3,054	1,718	6,882	1,718
Consolidated net operating income		(2,264)	(541)	(4,707)	250
Depreciation and amortization		0	0	0	0
Interest expense		106,803	105,766	318,807	328,935
General and administrative expenses		32,256	31,003	93,618	100,546
Loss (gain) on derivatives and financial instruments, net		0	0	0	0
Provision for loan losses, net		0	0	0	0
Impairment of assets		0	0	0	0
Other expenses		1,734	1,470	6,344	8,722
Income (loss) from continuing operations before income taxes and other items		(143,057)	(171,784)	(475,982)	(470,957)
Income tax (expense) benefit		(4,940)	(2,003)	(6,662)	(9,678)
Income (loss) from unconsolidated entities		0	0	0	0
Gain (loss) on real estate dispositions, net		0	0	0	0
Income (loss) from continuing operations		(147,997)	(173,787)	(482,644)	(480,635)
Net income (loss)		(147,997)	(173,787)	(482,644)	(480,635)
Total assets		173,503		173,503
Loss (gain) on extinguishment of debt, net		0	33,004	52,506	33,004
Non-segment / Corporate | Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		0	0	0	0
Non-segment / Corporate | Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		0	0	0	0
Non-segment / Corporate | Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		$ 790	$ 1,177	$ 2,175	$ 1,968