Segment Reporting (Segment Information for Reportable Segments) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Rental income									$ 1,588,400
Rental income										$ 1,380,422	$ 1,445,871
Total revenues	$ 1,262,822	$ 1,266,133	$ 1,320,106	$ 1,272,245	$ 1,241,243	$ 1,236,379	$ 1,125,912	$ 1,096,965	5,121,306	4,700,499	4,316,641
Property operating expenses									2,690,042	2,433,017	2,083,925
Consolidated net operating income									2,431,264	2,267,482	2,232,716
Depreciation and amortization									1,027,073	950,459	921,720
Interest expense									555,559	526,592	484,622
General and administrative expenses									126,549	126,383	122,008
Loss (gain) on derivatives and financial instruments, net									(4,399)	(4,016)	2,284
Loss (gain) on extinguishment of debt, net									84,155	16,097	37,241
Provision for loan losses									18,690	0	62,966
Impairment of assets									28,133	115,579	124,483
Other expenses									52,612	112,898	177,776
Income (loss) from continuing operations before income taxes and other items									542,892	423,490	299,616
Income tax (expense) benefit									(2,957)	(8,674)	(20,128)
(Loss) income from unconsolidated entities									42,434	(641)	(83,125)
Gain (loss) on real estate dispositions, net									748,041	415,575	344,250
Income (loss) from continuing operations									1,330,410	829,750	540,613
Net income									1,330,410	829,750	540,613
Total assets	33,380,751				30,342,072				33,380,751	30,342,072
Non capitalizable transaction cost										81,116	88,316
Other than temporary asset impairment charges											18,294
Expense recognized for the donation of the corporate headquarters											40,730
Non-segment / Corporate
Segment Reporting Information [Line Items]
Rental income									0
Rental income										0	0
Total revenues									3,966	2,275	1,538
Property operating expenses									0	0	0
Consolidated net operating income									3,966	2,275	1,538
Depreciation and amortization									0	0	0
Interest expense									461,273	436,256	396,148
General and administrative expenses									126,549	126,383	122,008
Loss (gain) on derivatives and financial instruments, net									0	0	0
Loss (gain) on extinguishment of debt, net									82,541	4,091	0
Provision for loan losses									0		0
Impairment of assets									0	0	0
Other expenses									10,705	7,729	50,829
Income (loss) from continuing operations before income taxes and other items									(677,102)	(572,184)	(567,447)
Income tax (expense) benefit									(2,284)	(11,362)	2,070
(Loss) income from unconsolidated entities									0	0	0
Gain (loss) on real estate dispositions, net									0	0	0
Income (loss) from continuing operations									(679,386)	(583,546)	(565,377)
Net income									(679,386)	(583,546)	(565,377)
Total assets	169,515				196,908				169,515	196,908
Seniors Housing Operating | Operating Segments
Segment Reporting Information [Line Items]
Rental income									0
Rental income										0	0
Total revenues									3,456,869	3,240,454	2,784,619
Property operating expenses									2,417,349	2,255,432	1,904,593
Consolidated net operating income									1,039,520	985,022	880,026
Depreciation and amortization									553,189	529,449	484,796
Interest expense									67,983	69,060	63,265
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									1,614	110	3,785
Provision for loan losses									0		0
Impairment of assets									2,145	7,599	21,949
Other expenses									26,348	6,624	8,347
Income (loss) from continuing operations before income taxes and other items									388,241	372,180	297,884
Income tax (expense) benefit									6,246	1,202	(16,430)
(Loss) income from unconsolidated entities									12,388	(28,142)	(105,236)
Gain (loss) on real estate dispositions, net									528,747	(2,245)	56,295
Income (loss) from continuing operations									935,622	342,995	232,513
Net income									935,622	342,995	232,513
Total assets	15,784,898				14,607,127				15,784,898	14,607,127
Triple-net | Operating Segments
Segment Reporting Information [Line Items]
Rental income									903,798
Rental income										828,865	885,811
Total revenues									972,643	900,964	967,084
Property operating expenses									53,900	915	0
Consolidated net operating income									918,743	900,049	967,084
Depreciation and amortization									232,626	235,480	243,830
Interest expense									12,892	14,225	15,194
General and administrative expenses									0	0	0
Loss (gain) on derivatives and financial instruments, net									(4,399)	(4,016)	2,284
Loss (gain) on extinguishment of debt, net									0	(32)	29,083
Provision for loan losses									18,690		62,966
Impairment of assets									11,926	107,980	96,909
Other expenses									13,771	90,975	116,689
Income (loss) from continuing operations before income taxes and other items									633,237	455,437	400,129
Income tax (expense) benefit									(4,209)	1,611	(4,291)
(Loss) income from unconsolidated entities									22,985	21,938	19,428
Gain (loss) on real estate dispositions, net									218,322	196,589	286,325
Income (loss) from continuing operations									870,335	675,575	701,591
Net income									870,335	675,575	701,591
Total assets	9,434,817				10,111,227				9,434,817	10,111,227
Outpatient Medical | Operating Segments
Segment Reporting Information [Line Items]
Rental income									684,602
Rental income										551,557	560,060
Total revenues									687,828	556,806	563,400
Property operating expenses									218,793	176,670	179,332
Consolidated net operating income									469,035	380,136	384,068
Depreciation and amortization									241,258	185,530	193,094
Interest expense									13,411	7,051	10,015
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									0	11,928	4,373
Provision for loan losses									0		0
Impairment of assets									14,062	0	5,625
Other expenses									1,788	7,570	1,911
Income (loss) from continuing operations before income taxes and other items									198,516	168,057	169,050
Income tax (expense) benefit									(2,710)	(125)	(1,477)
(Loss) income from unconsolidated entities									7,061	5,563	2,683
Gain (loss) on real estate dispositions, net									972	221,231	1,630
Income (loss) from continuing operations									203,839	394,726	171,886
Net income									203,839	394,726	171,886
Total assets	$ 7,991,521				$ 5,426,810				7,991,521	5,426,810
Resident fees and services
Segment Reporting Information [Line Items]
Revenue from contract with customer									3,448,175	3,234,852	2,779,423
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									3,448,175	3,234,852	2,779,423
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									63,830	55,814	73,811
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									36	578	69
Interest income | Triple-net | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									62,599	54,926	73,742
Interest income | Outpatient Medical | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									1,195	310	0
Other income
Segment Reporting Information [Line Items]
Revenue from contract with customer									20,901	29,411	17,536
Other income | Non-segment / Corporate
Segment Reporting Information [Line Items]
Revenue from contract with customer									3,966	2,275	1,538
Other income | Seniors Housing Operating | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									8,658	5,024	5,127
Other income | Triple-net | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									6,246	17,173	7,531
Other income | Outpatient Medical | Operating Segments
Segment Reporting Information [Line Items]
Revenue from contract with customer									$ 2,031	$ 4,939	$ 3,340