Segment Reporting - Summary Information for Reportable Segments (Details) $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2021 USD ($) segment	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment		3
Segment Reporting Information [Line Items]
Rental income		$ 302,843	$ 389,960
Total revenues		1,052,062	1,258,602
Property operating expenses		617,326	681,781
Consolidated net operating income		434,736	576,821
Depreciation and amortization		244,426	274,801
Interest expense		123,142	142,007
General and administrative expenses		29,926	35,481
Loss (gain) on derivatives and financial instruments, net		1,934	7,651
Provision for loan losses	$ 6,898	1,383	7,072
Impairment of assets		23,568	27,827
Other expenses		10,994	6,292
Income (loss) from continuing operations before income taxes and other items		4,006	75,690
Income tax (expense) benefit		(3,943)	(5,442)
Income (loss) from unconsolidated entities		13,049	(3,692)
Gain (loss) on real estate dispositions, net		59,080	262,824
Income (loss) from continuing operations		72,192	329,380
Net income (loss)		72,192	329,380
Total assets		32,992,251		$ 32,483,642
Loss (gain) on extinguishment of debt, net		(4,643)	0
Straight Line Rent		(30,563)	2,119
Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		723,464	849,972
Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		19,579	15,241
Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		6,176	3,429
Operating Segments | Seniors Housing Operating
Segment Reporting Information [Line Items]
Rental income		0	0
Total revenues		726,402	851,128
Property operating expenses		555,968	607,871
Consolidated net operating income		170,434	243,257
Depreciation and amortization		132,586	146,774
Interest expense		11,418	16,434
General and administrative expenses		0	0
Loss (gain) on derivatives and financial instruments, net		0	0
Provision for loan losses		251	0
Impairment of assets		4,604	3,495
Other expenses		3,459	2,989
Income (loss) from continuing operations before income taxes and other items		22,759	73,565
Income tax (expense) benefit		0	0
Income (loss) from unconsolidated entities		5,234	(11,024)
Gain (loss) on real estate dispositions, net		5,195	(149)
Income (loss) from continuing operations		33,188	62,392
Net income (loss)		33,188	62,392
Total assets		16,032,225
Loss (gain) on extinguishment of debt, net		(4,643)
Operating Segments | Seniors Housing Operating | Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		723,464	849,972
Operating Segments | Seniors Housing Operating | Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		1,119	104
Operating Segments | Seniors Housing Operating | Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		1,819	1,052
Operating Segments | Triple-net
Segment Reporting Information [Line Items]
Rental income		152,463	191,385
Total revenues		168,482	207,729
Property operating expenses		12,841	13,302
Consolidated net operating income		155,641	194,427
Depreciation and amortization		56,667	57,694
Interest expense		1,882	2,852
General and administrative expenses		0	0
Loss (gain) on derivatives and financial instruments, net		1,934	7,651
Provision for loan losses		853	7,072
Impairment of assets		18,964	24,332
Other expenses		4,983	513
Income (loss) from continuing operations before income taxes and other items		70,358	94,313
Income tax (expense) benefit		0	0
Income (loss) from unconsolidated entities		4,907	5,796
Gain (loss) on real estate dispositions, net		2,042	49,637
Income (loss) from continuing operations		77,307	149,746
Net income (loss)		77,307	149,746
Total assets		8,660,043
Loss (gain) on extinguishment of debt, net		0
Operating Segments | Triple-net | Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		0	0
Operating Segments | Triple-net | Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		14,922	14,671
Operating Segments | Triple-net | Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		1,097	1,673
Operating Segments | Outpatient Medical
Segment Reporting Information [Line Items]
Rental income		150,380	198,575
Total revenues		156,223	199,329
Property operating expenses		46,863	60,608
Consolidated net operating income		109,360	138,721
Depreciation and amortization		55,173	70,333
Interest expense		4,015	4,808
General and administrative expenses		0	0
Loss (gain) on derivatives and financial instruments, net		0	0
Provision for loan losses		279	0
Impairment of assets		0	0
Other expenses		712	1,007
Income (loss) from continuing operations before income taxes and other items		49,181	62,573
Income tax (expense) benefit		0	0
Income (loss) from unconsolidated entities		2,908	1,536
Gain (loss) on real estate dispositions, net		51,843	213,336
Income (loss) from continuing operations		103,932	277,445
Net income (loss)		103,932	277,445
Total assets		6,380,835
Loss (gain) on extinguishment of debt, net		0
Operating Segments | Outpatient Medical | Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		0	0
Operating Segments | Outpatient Medical | Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		3,538	466
Operating Segments | Outpatient Medical | Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		2,305	288
Non-segment / Corporate
Segment Reporting Information [Line Items]
Rental income		0	0
Total revenues		955	416
Property operating expenses		1,654	0
Consolidated net operating income		(699)	416
Depreciation and amortization		0	0
Interest expense		105,827	117,913
General and administrative expenses		29,926	35,481
Loss (gain) on derivatives and financial instruments, net		0	0
Provision for loan losses		0	0
Impairment of assets		0	0
Other expenses		1,840	1,783
Income (loss) from continuing operations before income taxes and other items		(138,292)	(154,761)
Income tax (expense) benefit		(3,943)	(5,442)
Income (loss) from unconsolidated entities		0	0
Gain (loss) on real estate dispositions, net		0	0
Income (loss) from continuing operations		(142,235)	(160,203)
Net income (loss)		(142,235)	(160,203)
Total assets		1,919,148
Loss (gain) on extinguishment of debt, net		0
Non-segment / Corporate | Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer		0	0
Non-segment / Corporate | Interest income
Segment Reporting Information [Line Items]
Revenue from contract with customer		0	0
Non-segment / Corporate | Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer		$ 955	$ 416