Segment Reporting - Segment Information for Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Rental income	$ 1,374,695	$ 1,443,360	$ 1,588,400
Total revenues	4,742,115	4,605,967	5,121,306
Property operating expenses	2,774,562	2,597,823	2,690,042
Consolidated net operating income (loss)	1,967,553	2,008,144	2,431,264
Depreciation and amortization	1,037,566	1,038,437	1,027,073
Interest expense	489,853	514,388	555,559
General and administrative expenses	126,727	128,394	126,549
Loss (gain) on derivatives and financial instruments, net	(7,333)	11,049	(4,399)
Loss (gain) on extinguishment of debt, net	49,874	47,049	84,155
Provision for loan losses, net	7,270	94,436	18,690
Impairment of assets	51,107	135,608	28,133
Other expenses	41,739	70,335	52,612
Income (loss) from continuing operations before income taxes and other items	170,750	(31,552)	542,892
Income tax (expense) benefit	(8,713)	(9,968)	(2,957)
Income (loss) from unconsolidated entities	(22,933)	(8,083)	42,434
Gain (loss) on real estate dispositions, net	235,375	1,088,455	748,041
Income (loss) from continuing operations	374,479	1,038,852	1,330,410
Net income (loss)	374,479	1,038,852	1,330,410
Total assets	34,910,325	32,483,642
Non-segment / Corporate
Segment Reporting Information [Line Items]
Rental income	0	0	0
Total revenues	2,992	2,781	3,966
Property operating expenses	8,817	3,381	0
Consolidated net operating income (loss)	(5,825)	(600)	3,966
Depreciation and amortization	0	0	0
Interest expense	426,644	432,431	461,273
General and administrative expenses	126,727	128,394	126,549
Loss (gain) on derivatives and financial instruments, net	0	0	0
Loss (gain) on extinguishment of debt, net	52,506	33,344	82,541
Provision for loan losses, net	0	0	0
Impairment of assets	0	0	0
Other expenses	7,895	24,929	10,705
Income (loss) from continuing operations before income taxes and other items	(619,597)	(619,698)	(677,102)
Income tax (expense) benefit	(8,713)	(9,968)	(2,957)
Income (loss) from unconsolidated entities	0	0	0
Gain (loss) on real estate dispositions, net	0	0	0
Income (loss) from continuing operations	(628,310)	(629,666)	(680,059)
Net income (loss)	(628,310)	(629,666)	(680,059)
Total assets	144,068	1,369,127
Seniors Housing Operating | Operating Segments
Segment Reporting Information [Line Items]
Rental income	0	0	0
Total revenues	3,213,250	3,081,863	3,456,869
Property operating expenses	2,529,344	2,326,311	2,417,349
Consolidated net operating income (loss)	683,906	755,552	1,039,520
Depreciation and amortization	593,565	544,462	553,189
Interest expense	39,327	54,901	67,983
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	(2,628)	12,659	1,614
Provision for loan losses, net	394	671	0
Impairment of assets	22,317	100,741	2,145
Other expenses	27,132	14,265	26,348
Income (loss) from continuing operations before income taxes and other items	3,799	27,853	388,241
Income tax (expense) benefit	0	0	0
Income (loss) from unconsolidated entities	(39,225)	(33,857)	12,388
Gain (loss) on real estate dispositions, net	6,146	328,249	528,747
Income (loss) from continuing operations	(29,280)	322,245	929,376
Net income (loss)	(29,280)	322,245	929,376
Total assets	18,851,999	16,044,153
Triple-net | Operating Segments
Segment Reporting Information [Line Items]
Rental income	761,441	733,776	903,798
Total revenues	890,584	801,304	972,643
Property operating expenses	49,462	53,183	53,900
Consolidated net operating income (loss)	841,122	748,121	918,743
Depreciation and amortization	220,699	232,604	232,626
Interest expense	6,376	9,477	12,892
General and administrative expenses	0	0	0
Loss (gain) on derivatives and financial instruments, net	(7,333)	11,049	(4,399)
Loss (gain) on extinguishment of debt, net	0	0	0
Provision for loan losses, net	10,339	90,563	18,690
Impairment of assets	26,579	34,867	11,926
Other expenses	4,189	22,923	13,771
Income (loss) from continuing operations before income taxes and other items	580,273	346,638	633,237
Income tax (expense) benefit	0	0	0
Income (loss) from unconsolidated entities	20,687	18,462	22,985
Gain (loss) on real estate dispositions, net	135,881	64,288	218,322
Income (loss) from continuing operations	736,841	429,388	874,544
Net income (loss)	736,841	429,388	874,544
Total assets	9,710,194	8,547,482
Outpatient Medical | Operating Segments
Segment Reporting Information [Line Items]
Rental income	613,254	709,584	684,602
Total revenues	635,289	720,019	687,828
Property operating expenses	186,939	214,948	218,793
Consolidated net operating income (loss)	448,350	505,071	469,035
Depreciation and amortization	223,302	261,371	241,258
Interest expense	17,506	17,579	13,411
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	(4)	1,046	0
Provision for loan losses, net	(3,463)	3,202	0
Impairment of assets	2,211	0	14,062
Other expenses	2,523	8,218	1,788
Income (loss) from continuing operations before income taxes and other items	206,275	213,655	198,516
Income tax (expense) benefit	0	0	0
Income (loss) from unconsolidated entities	(4,395)	7,312	7,061
Gain (loss) on real estate dispositions, net	93,348	695,918	972
Income (loss) from continuing operations	295,228	916,885	206,549
Net income (loss)	295,228	916,885	206,549
Total assets	6,204,064	6,522,880
Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer	3,197,223	3,074,022	3,448,175
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	3,197,223	3,074,022	3,448,175
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	137,563	69,156	63,830
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	4,231	618	36
Interest income | Triple-net | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer	124,540	62,625	62,599
Interest income | Outpatient Medical | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer	8,792	5,913	1,195
Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer	32,634	19,429	20,901
Other income | Non-segment / Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer	2,992	2,781	3,966
Other income | Seniors Housing Operating | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer	11,796	7,223	8,658
Other income | Triple-net | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer	4,603	4,903	6,246
Other income | Outpatient Medical | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer	$ 13,243	$ 4,522	$ 2,031