Segment Reporting (Segment Information for Reportable Segments) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Rental income									$ 1,443,360	$ 1,588,400	$ 1,380,422
Total revenues	$ 1,122,016	$ 1,036,874	$ 1,188,475	$ 1,258,602	$ 1,262,822	$ 1,266,133	$ 1,320,106	$ 1,272,245	4,605,967	5,121,306	4,700,499
Property operating expenses									2,597,823	2,690,042	2,433,017
Consolidated net operating income									2,008,144	2,431,264	2,267,482
Depreciation and amortization									1,038,437	1,027,073	950,459
Interest expense									514,388	555,559	526,592
General and administrative expenses									128,394	126,549	126,383
Loss (gain) on derivatives and financial instruments, net									11,049	(4,399)	(4,016)
Loss (gain) on extinguishment of debt, net									47,049	84,155	16,097
Provision for loan losses									94,436	18,690	0
Impairment of assets									135,608	28,133	115,579
Other expenses									70,335	52,612	112,898
Income (loss) from continuing operations before income taxes and other items									(31,552)	542,892	423,490
Income tax (expense) benefit									(9,968)	(2,957)	(8,674)
Income (loss) from unconsolidated entities									(8,083)	42,434	(641)
Gain (loss) on real estate dispositions, net									1,088,455	748,041	415,575
Income (loss) from continuing operations									1,038,852	1,330,410	829,750
Net income									1,038,852	1,330,410	829,750
Total assets	32,483,642				33,380,751				32,483,642	33,380,751
Non capitalizable transaction cost											81,116
Depreciation and amortization									1,038,437	1,027,073	950,459
Non-segment / Corporate
Segment Reporting Information [Line Items]
Rental income									0	0	0
Total revenues									2,781	3,966	2,275
Property operating expenses									3,381	0	0
Consolidated net operating income									(600)	3,966	2,275
Interest expense									432,431	461,273	436,256
General and administrative expenses									128,394	126,549	126,383
Loss (gain) on derivatives and financial instruments, net									0	0	0
Loss (gain) on extinguishment of debt, net									33,344	82,541	4,091
Provision for loan losses									0	0
Impairment of assets									0	0	0
Other expenses									24,929	10,705	7,729
Income (loss) from continuing operations before income taxes and other items									(619,698)	(677,102)	(572,184)
Income tax (expense) benefit									(9,968)	(2,957)	(8,674)
Income (loss) from unconsolidated entities									0	0	0
Gain (loss) on real estate dispositions, net									0	0	0
Income (loss) from continuing operations									(629,666)	(680,059)	(580,858)
Net income									(629,666)	(680,059)	(580,858)
Total assets	1,369,127				169,515				1,369,127	169,515
Depreciation and amortization									0	0	0
Seniors Housing Operating | Operating Segments
Segment Reporting Information [Line Items]
Rental income									0	0	0
Total revenues									3,081,863	3,456,869	3,240,454
Property operating expenses									2,326,311	2,417,349	2,255,432
Consolidated net operating income									755,552	1,039,520	985,022
Interest expense									54,901	67,983	69,060
General and administrative expenses									0	0	0
Loss (gain) on derivatives and financial instruments, net									0	0	0
Loss (gain) on extinguishment of debt, net									12,659	1,614	110
Provision for loan losses									671	0
Impairment of assets									100,741	2,145	7,599
Other expenses									14,265	26,348	6,624
Income (loss) from continuing operations before income taxes and other items									27,853	388,241	372,180
Income tax (expense) benefit									0	0	0
Income (loss) from unconsolidated entities									(33,857)	12,388	(28,142)
Gain (loss) on real estate dispositions, net									328,249	528,747	(2,245)
Income (loss) from continuing operations									322,245	929,376	341,793
Net income									322,245	929,376	341,793
Total assets	16,044,153				15,784,898				16,044,153	15,784,898
Depreciation and amortization									544,462	553,189	529,449
Triple-net | Operating Segments
Segment Reporting Information [Line Items]
Rental income									733,776	903,798	828,865
Total revenues									801,304	972,643	900,964
Property operating expenses									53,183	53,900	915
Consolidated net operating income									748,121	918,743	900,049
Interest expense									9,477	12,892	14,225
General and administrative expenses									0	0	0
Loss (gain) on derivatives and financial instruments, net									11,049	(4,399)	(4,016)
Loss (gain) on extinguishment of debt, net									0	0	(32)
Provision for loan losses									90,563	18,690
Impairment of assets									34,867	11,926	107,980
Other expenses									22,923	13,771	90,975
Income (loss) from continuing operations before income taxes and other items									346,638	633,237	455,437
Income tax (expense) benefit									0	0	0
Income (loss) from unconsolidated entities									18,462	22,985	21,938
Gain (loss) on real estate dispositions, net									64,288	218,322	196,589
Income (loss) from continuing operations									429,388	874,544	673,964
Net income									429,388	874,544	673,964
Total assets	8,547,482				9,434,817				8,547,482	9,434,817
Depreciation and amortization									232,604	232,626	235,480
Outpatient Medical | Operating Segments
Segment Reporting Information [Line Items]
Rental income									709,584	684,602	551,557
Total revenues									720,019	687,828	556,806
Property operating expenses									214,948	218,793	176,670
Consolidated net operating income									505,071	469,035	380,136
Interest expense									17,579	13,411	7,051
General and administrative expenses									0	0	0
Loss (gain) on derivatives and financial instruments, net									0	0	0
Loss (gain) on extinguishment of debt, net									1,046	0	11,928
Provision for loan losses									3,202	0
Impairment of assets									0	14,062	0
Other expenses									8,218	1,788	7,570
Income (loss) from continuing operations before income taxes and other items									213,655	198,516	168,057
Income tax (expense) benefit									0	0	0
Income (loss) from unconsolidated entities									7,312	7,061	5,563
Gain (loss) on real estate dispositions, net									695,918	972	221,231
Income (loss) from continuing operations									916,885	206,549	394,851
Net income									916,885	206,549	394,851
Total assets	$ 6,522,880				$ 7,991,521				6,522,880	7,991,521
Depreciation and amortization									261,371	241,258	185,530
Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer									3,074,022	3,448,175	3,234,852
Resident fees and services | Non-segment / Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer									0	0	0
Resident fees and services | Seniors Housing Operating | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									3,074,022	3,448,175	3,234,852
Resident fees and services | Triple-net | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									0	0	0
Resident fees and services | Outpatient Medical | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									0	0	0
Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer									69,156	63,830	55,814
Interest income | Non-segment / Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer									0	0	0
Interest income | Seniors Housing Operating | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									618	36	578
Interest income | Triple-net | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									62,625	62,599	54,926
Interest income | Outpatient Medical | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									5,913	1,195	310
Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer									19,429	20,901	29,411
Other income | Non-segment / Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer									2,781	3,966	2,275
Other income | Seniors Housing Operating | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									7,223	8,658	5,024
Other income | Triple-net | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									4,903	6,246	17,173
Other income | Outpatient Medical | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									$ 4,522	$ 2,031	$ 4,939