Segment Reporting (Details) $ in Thousands	3 Months Ended										12 Months Ended
	Dec. 31, 2017 USD ($)		Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	[2]	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Summary of information for reportable segments
Rental income											$ 1,445,871		$ 1,648,815	$ 1,598,948
Resident fees and services											2,779,423		2,504,731	2,158,031
Interest income											73,811		97,963	84,141
Other income											17,536		29,651	18,706
Total revenues	$ 1,104,257	[1]	$ 1,091,483	$ 1,058,602	$ 1,062,298	$ 1,078,321	$ 1,079,133		$ 1,076,657	$ 1,047,050	4,316,641		4,281,160	3,859,826
Property operating expenses											2,083,925		1,876,983	1,622,257
Net Operating Income, Total											2,232,716	[3]	2,404,177	2,237,569
Interest expense											484,622		521,345	492,169
Loss (gain) on derivatives, net											2,284		(2,448)	(58,427)
Depreciation and amortization expenses											921,720		901,242	826,240
General and administrative											122,008		155,241	147,416
Transaction costs											0		42,910	110,926
Loss (gain) on extinguishment of debt, net											37,241		17,214	34,677
Provision for loan losses	62,966										62,966		10,215	0
Impairment of asset	99,821										124,483		37,207	2,220
Other expenses											177,776		11,998	46,231
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Cumulative Effects of Changes in Accounting Principles, Noncontrolling Interest, Total											299,616		709,253	636,117
Income tax (expense) benefit											(20,128)		19,128	(6,451)
(Loss) income from unconsolidated entities											(83,125)		(10,357)	(21,504)
Income (loss) from continuing operations											196,363		718,024	608,162
Gain (loss) on real estate dispositions, net											344,250		364,046	280,387
Net income (loss)											540,613		1,082,070	$ 888,549
Total assets	$ 27,944,445					$ 28,865,184					$ 27,944,445		$ 28,865,184
Segment Reporting (Textuals)
Percent of Assets	1					1					1		1
Percent of Revenues											1		1	1
United States
Summary of information for reportable segments
Total revenues											$ 3,464,527		$ 3,453,485	$ 3,133,327
Total assets	$ 22,274,443					$ 23,572,459					$ 22,274,443		$ 23,572,459
Segment Reporting (Textuals)
Percent of Assets	0.797					0.817					0.797		0.817
Percent of Revenues											0.803		0.806	0.811
United Kingdom
Summary of information for reportable segments
Total revenues											$ 407,351		$ 388,383	$ 407,745
Total assets	$ 3,239,039					$ 2,782,489					$ 3,239,039		$ 2,782,489
Segment Reporting (Textuals)
Percent of Assets	0.116					0.096					0.116		0.096
Percent of Revenues											0.094		0.091	0.106
Canada
Summary of information for reportable segments
Total revenues											$ 444,763		$ 439,292	$ 318,754
Total assets	$ 2,430,963					$ 2,510,236					$ 2,430,963		$ 2,510,236
Segment Reporting (Textuals)
Percent of Assets	0.087					0.087					0.087		0.087
Percent of Revenues											0.103		0.103	0.083
Triple Net [Member]
Summary of information for reportable segments
Rental income											$ 885,811		$ 1,112,325	$ 1,094,827
Resident fees and services											0		0	0
Interest income											73,742		90,476	74,108
Other income											7,531		6,059	6,871
Total revenues											967,084		1,208,860	1,175,806
Property operating expenses											0		0	0
Net Operating Income, Total											967,084		1,208,860	1,175,806
Interest expense											15,194		21,370	28,384
Loss (gain) on derivatives, net											2,284		68	(58,427)
Depreciation and amortization expenses											243,830		297,197	288,242
General and administrative											0		0	0
Transaction costs													10,016	53,195
Loss (gain) on extinguishment of debt, net											29,083		863	10,095
Provision for loan losses											62,966		6,935
Impairment of asset											96,909		20,169	2,220
Other expenses											116,689	[4]	0	35,648
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Cumulative Effects of Changes in Accounting Principles, Noncontrolling Interest, Total											400,129		852,242	816,449
Income tax (expense) benefit											(4,291)		(1,087)	(4,244)
(Loss) income from unconsolidated entities											19,428		9,767	8,260
Income (loss) from continuing operations											415,266		860,922	820,465
Gain (loss) on real estate dispositions, net											286,325		355,394	86,261
Net income (loss)											701,591		1,216,316	906,726
Total assets	$ 9,325,344					$ 10,713,032					9,325,344		10,713,032
Seniors Housing Operating [Member]
Summary of information for reportable segments
Rental income											0		0	0
Resident fees and services											2,779,423		2,504,731	2,158,031
Interest income											69		4,180	4,180
Other income											5,127		17,085	6,060
Total revenues											2,784,619		2,525,996	2,168,271
Property operating expenses											1,904,593		1,711,882	1,467,009
Net Operating Income, Total											880,026		814,114	701,262
Interest expense											63,265		81,853	70,388
Loss (gain) on derivatives, net											0		0	0
Depreciation and amortization expenses											484,796		415,429	351,733
General and administrative											0		0	0
Transaction costs													29,207	54,966
Loss (gain) on extinguishment of debt, net											3,785		(88)	(195)
Provision for loan losses											0		0
Impairment of asset											21,949		12,403	0
Other expenses											8,347		0	0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Cumulative Effects of Changes in Accounting Principles, Noncontrolling Interest, Total											297,884		275,310	224,370
Income tax (expense) benefit											(16,430)		(3,762)	986
(Loss) income from unconsolidated entities											(105,236)		(20,442)	(32,672)
Income (loss) from continuing operations											176,218		251,106	192,684
Gain (loss) on real estate dispositions, net											56,295		9,880	0
Net income (loss)											232,513		260,986	192,684
Total assets	13,432,001					12,851,414					13,432,001		12,851,414
Outpatient Medical [Member]
Summary of information for reportable segments
Rental income											560,060		536,490	504,121
Resident fees and services											0		0	0
Interest income											0		3,307	5,853
Other income											3,340		5,568	4,684
Total revenues											563,400		545,365	514,658
Property operating expenses											179,332		165,101	155,248
Net Operating Income, Total											384,068		380,264	359,410
Interest expense											10,015		19,087	27,542
Loss (gain) on derivatives, net											0		0	0
Depreciation and amortization expenses											193,094		188,616	186,265
General and administrative											0		0	0
Transaction costs													3,687	2,765
Loss (gain) on extinguishment of debt, net											4,373		0	0
Provision for loan losses											0		3,280
Impairment of asset											5,625		4,635	0
Other expenses											1,911		0	0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Cumulative Effects of Changes in Accounting Principles, Noncontrolling Interest, Total											169,050		160,959	142,838
Income tax (expense) benefit											(1,477)		(511)	245
(Loss) income from unconsolidated entities											2,683		318	2,908
Income (loss) from continuing operations											170,256		160,766	145,991
Gain (loss) on real estate dispositions, net											1,630		(1,228)	194,126
Net income (loss)											171,886		159,538	340,117
Total assets	5,082,145					4,951,538					5,082,145		4,951,538
Corporate, Non-Segment [Member]
Summary of information for reportable segments
Rental income											0		0	0
Resident fees and services											0		0	0
Interest income											0		0	0
Other income											1,538		939	1,091
Total revenues											1,538		939	1,091
Property operating expenses											0		0	0
Net Operating Income, Total											1,538		939	1,091
Interest expense											396,148		399,035	365,855
Loss (gain) on derivatives, net											0		(2,516)	0
Depreciation and amortization expenses											0		0	0
General and administrative											122,008		155,241	147,416
Transaction costs													0	0
Loss (gain) on extinguishment of debt, net											0		16,439	24,777
Provision for loan losses											0		0
Impairment of asset											0		0	0
Other expenses											50,829	[5]	11,998	10,583
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Cumulative Effects of Changes in Accounting Principles, Noncontrolling Interest, Total											(567,447)		(579,258)	(547,540)
Income tax (expense) benefit											2,070		24,488	(3,438)
(Loss) income from unconsolidated entities											0		0	0
Income (loss) from continuing operations											(565,377)		(554,770)	(550,978)
Gain (loss) on real estate dispositions, net											0		0	0
Net income (loss)											(565,377)		(554,770)	$ (550,978)
Total assets	$ 104,955					$ 349,200					$ 104,955		$ 349,200

[1] The decrease in net income (loss) and amounts per share are primarily attributable to $99,821,100 impairment of assets and $62,966,000 provision for loan losses recognized in the fourth quarter as compared to none in the third quarter.

[2] The increase in net income and amounts per share are primarily attributable to gains on sales of real estate of $162,351,000 for the third quarter as compared to gains of $1,530,000 for the second quarter.

[3] Genesis HealthCare is in our triple-net segment. Sunrise Senior Living and Revera are in our seniors housing operating segment. Brookdale Senior Living and Benchmark Senior Living are in both our triple-net and seniors housing operating segments.

[4] Primarily represents non-capitalizable transaction costs, including $88,316,000 due to a joint venture transaction with an existing seniors housing operator which converted a portfolio of properties from triple-net to seniors housing operating, an exchange of PropCo/OpCo interests, and termination/restructuring of pre-existing relationships. In addition, includes $18,294,000 other than temporary impairment charge on the Genesis available-for-sale equity investment (see also Notes 11 and 16).

[5] Primarily related to $40,730,000 recognized for the donation of the corporate headquarters. See also Note 12.