Segment Reporting - Summary Information for Reportable Segments (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) segment	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	[1]
Segment Reporting [Abstract]
Number of operating segments | segment				3
Segment Reporting Information [Line Items]
Rental income		$ 354,723	$ 396,305	$ 657,566	$ 786,265
Total revenues		1,140,992	1,188,475	2,193,054	2,447,077
Property operating expenses		642,657	660,764	1,259,983	1,342,545
Consolidated net operating income		498,335	527,711	933,071	1,104,532
Depreciation and amortization		240,885	265,371	485,311	540,172
Interest expense		122,341	126,357	245,483	268,364
General and administrative expenses		31,436	34,062	61,362	69,543
Loss (gain) on derivatives and financial instruments, net		(359)	1,434	1,575	9,085
Provision for loan losses	$ 6,898	6,197	1,422	7,580	8,494
Impairment of assets		23,692	75,151	47,260	102,978
Other expenses		11,687	19,411	22,681	25,703
Income (loss) from continuing operations before income taxes and other items		6,844	4,254	10,850	79,944
Income tax (expense) benefit		2,221	(2,233)	(1,722)	(7,675)
Income (loss) from unconsolidated entities		(7,976)	1,332	5,073	(2,360)
Gain (loss) on real estate dispositions, net		44,668	155,863	103,748	418,687
Income (loss) from continuing operations		45,757	159,216	117,949	488,596
Net income (loss)		45,757	159,216	117,949	488,596
Total assets		32,176,116		32,176,116		$ 32,483,642
Loss (gain) on extinguishment of debt, net		55,612	249	50,969	249
Straight Line Rent				(9,688)	25,959
Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		740,891	769,560	1,464,355	1,619,532
Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		38,448	16,069	58,027	31,310
Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		6,930	6,541	13,106	9,970
Operating Segments | Seniors Housing Operating
Segment Reporting Information [Line Items]
Rental income		0	0	0	0
Total revenues		742,549	773,650	1,468,951	1,624,778
Property operating expenses		582,361	595,513	1,138,329	1,203,384
Consolidated net operating income		160,188	178,137	330,622	421,394
Depreciation and amortization		131,035	139,163	263,621	285,937
Interest expense		10,553	14,029	21,971	30,463
General and administrative expenses		0	0	0	0
Loss (gain) on derivatives and financial instruments, net		0	0	0	0
Provision for loan losses		(181)	0	70	0
Impairment of assets		17,713	75,151	22,317	78,646
Other expenses		3,709	5,251	7,168	8,240
Income (loss) from continuing operations before income taxes and other items		(5,747)	(54,965)	17,012	18,600
Income tax (expense) benefit		0	0	0	0
Income (loss) from unconsolidated entities		(12,938)	(6,787)	(7,704)	(17,811)
Gain (loss) on real estate dispositions, net		(28)	14,465	5,167	14,316
Income (loss) from continuing operations		(18,713)	(47,287)	14,475	15,105
Net income (loss)		(18,713)	(47,287)	14,475	15,105
Total assets		16,129,367		16,129,367
Loss (gain) on extinguishment of debt, net		3,106	(492)	(1,537)	(492)
Operating Segments | Seniors Housing Operating | Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		740,891	769,560	1,464,355	1,619,532
Operating Segments | Seniors Housing Operating | Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		856	88	1,975	192
Operating Segments | Seniors Housing Operating | Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		802	4,002	2,621	5,054
Operating Segments | Triple-net
Segment Reporting Information [Line Items]
Rental income		204,725	217,492	357,188	408,877
Total revenues		238,941	233,619	407,423	441,348
Property operating expenses		12,627	13,563	25,468	26,865
Consolidated net operating income		226,314	220,056	381,955	414,483
Depreciation and amortization		54,406	58,138	111,073	115,832
Interest expense		1,704	2,746	3,586	5,598
General and administrative expenses		0	0	0	0
Loss (gain) on derivatives and financial instruments, net		(359)	1,434	1,575	9,085
Provision for loan losses		10,019	1,451	10,872	8,523
Impairment of assets		3,768	0	22,732	24,332
Other expenses		4,110	3,500	9,093	4,013
Income (loss) from continuing operations before income taxes and other items		152,666	152,787	223,024	247,100
Income tax (expense) benefit		0	0	0	0
Income (loss) from unconsolidated entities		4,877	6,403	9,784	12,199
Gain (loss) on real estate dispositions, net		42,709	2,148	44,751	51,785
Income (loss) from continuing operations		200,252	161,338	277,559	311,084
Net income (loss)		200,252	161,338	277,559	311,084
Total assets		9,490,724		9,490,724
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		32,861	15,520	47,783	30,191
Operating Segments | Triple-net | Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		1,355	607	2,452	2,280
Operating Segments | Outpatient Medical
Segment Reporting Information [Line Items]
Rental income		149,998	178,813	300,378	377,388
Total revenues		159,072	180,831	315,295	380,160
Property operating expenses		45,495	51,688	92,358	112,296
Consolidated net operating income		113,577	129,143	222,937	267,864
Depreciation and amortization		55,444	68,070	110,617	138,403
Interest expense		3,907	4,326	7,922	9,134
General and administrative expenses		0	0	0	0
Loss (gain) on derivatives and financial instruments, net		0	0	0	0
Provision for loan losses		(3,641)	(29)	(3,362)	(29)
Impairment of assets		2,211	0	2,211	0
Other expenses		1,098	6,456	1,810	7,463
Income (loss) from continuing operations before income taxes and other items		54,558	49,579	103,739	112,152
Income tax (expense) benefit		0	0	0	0
Income (loss) from unconsolidated entities		85	1,716	2,993	3,252
Gain (loss) on real estate dispositions, net		1,987	139,250	53,830	352,586
Income (loss) from continuing operations		56,630	190,545	160,562	467,990
Net income (loss)		56,630	190,545	160,562	467,990
Total assets		6,212,491		6,212,491
Loss (gain) on extinguishment of debt, net		0	741	0	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		4,731	461	8,269	927
Operating Segments | Outpatient Medical | Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		4,343	1,557	6,648	1,845
Non-segment / Corporate
Segment Reporting Information [Line Items]
Rental income		0	0	0	0
Total revenues		430	375	1,385	791
Property operating expenses		2,174	0	3,828	0
Consolidated net operating income		(1,744)	375	(2,443)	791
Depreciation and amortization		0	0	0	0
Interest expense		106,177	105,256	212,004	223,169
General and administrative expenses		31,436	34,062	61,362	69,543
Loss (gain) on derivatives and financial instruments, net		0	0	0	0
Provision for loan losses		0	0	0	0
Impairment of assets		0	0	0	0
Other expenses		2,770	4,204	4,610	5,987
Income (loss) from continuing operations before income taxes and other items		(194,633)	(143,147)	(332,925)	(297,908)
Income tax (expense) benefit		2,221	(2,233)	(1,722)	(7,675)
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		(192,412)	(145,380)	(334,647)	(305,583)
Net income (loss)		(192,412)	(145,380)	(334,647)	(305,583)
Total assets		343,534		343,534
Loss (gain) on extinguishment of debt, net		52,506	0	52,506	0
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		$ 430	$ 375	$ 1,385	$ 791

[1] Note: The consolidated balance sheet at December 31, 2020 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements.