Segment Disclosures - Summary Information for the Reportable Segments (Details) $ in Thousands	1 Months Ended	3 Months Ended							9 Months Ended
	Mar. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) facility	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($) facility	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) facility	Sep. 30, 2017 USD ($) facility
Segment reporting information, revenues
Rental revenues		$ 454,786				$ 442,249			$ 1,395,722	$ 1,354,145
Operating expenses		(181,207)				(155,338)			(527,625)	(467,582)
Segment NOI		273,579				286,911			868,097	886,563
Adjustments to NOI		(703)				(3,281)			(14,051)	(9,855)
Adjusted NOI		272,876				283,630			854,046	876,708
Addback adjustments		703				3,281			14,051	9,855
Interest income		1,236				11,774			9,048	50,974
Interest expense		(63,486)				(71,328)			(211,626)	(235,834)
Depreciation and amortization		(132,198)				(130,588)			(418,740)	(397,893)
General and administrative		(23,503)				(23,523)			(75,192)	(67,287)
Transaction costs		(4,489)				(580)			(9,088)	(2,504)
Recoveries (impairments), net		(5,268)				(25,328)			(19,180)	(82,010)
Gain (loss) on sales of real estate, net		95,332	$ 25,000		$ 34,000	5,182	$ 1,000	$ 45,000	162,211	322,852
Loss on debt extinguishments		(43,899)				(54,227)			(43,899)	(54,227)
Other income (expense), net		1,604				(10,556)			(37,017)	40,723
Income tax benefit (expense)		4,929				5,481			14,919	14,630
Equity income (loss) from unconsolidated JVs		(911)				1,062			(442)	4,571
Net income (loss)		102,926				(5,720)			239,091	480,558
Corporate and other assets
Segment reporting information, revenues
Rental revenues		0				0			0	0
Operating expenses		0				0			0	0
Segment NOI		0				0			0	0
Adjustments to NOI		0				0			0	0
Adjusted NOI		0				0			0	0
Addback adjustments		0				0			0	0
Interest income		0				0			0	0
Interest expense		(62,004)				(68,924)			(205,688)	(222,775)
Depreciation and amortization		0				0			0	0
General and administrative		(23,503)				(23,523)			(75,192)	(67,287)
Transaction costs		(4,489)				(580)			(9,088)	(2,504)
Recoveries (impairments), net		0				0			0	0
Gain (loss) on sales of real estate, net		0				0			0	0
Loss on debt extinguishments		(43,899)				(54,227)			(43,899)	(54,227)
Other income (expense), net		1,604				(10,556)			3,550	(10,172)
Income tax benefit (expense)		4,929				5,481			14,919	14,630
Equity income (loss) from unconsolidated JVs		0				0			0	0
Net income (loss)		$ (127,362)				$ (152,329)			$ (315,398)	$ (342,335)
Senior housing triple-net
Segment Disclosure
Number of SH NNN facilities transitioned to RIDEA structure | facility		6				3			16	4
Segment reporting information, revenues
Gain (loss) on sales of real estate, net	$ 170,000					$ 5,000
Senior housing triple-net | Operating segment
Segment reporting information, revenues
Rental revenues		$ 67,487				77,220			$ 212,489	$ 255,332
Operating expenses		(840)				(934)			(2,677)	(2,927)
Segment NOI		66,647				76,286			209,812	252,405
Adjustments to NOI		534				(600)			(323)	(2,844)
Adjusted NOI		67,181				75,686			209,489	249,561
Addback adjustments		(534)				600			323	2,844
Interest income		0				0			0	0
Interest expense		(599)				(640)			(1,806)	(1,898)
Depreciation and amortization		(18,884)				(25,547)			(62,041)	(77,478)
General and administrative		0				0			0	0
Transaction costs		0				0			0	0
Recoveries (impairments), net		0				0			(6,273)	0
Gain (loss) on sales of real estate, net		463				5,176			(22,687)	273,409
Loss on debt extinguishments		0				0			0	0
Other income (expense), net		0				0			0	0
Income tax benefit (expense)		0				0			0	0
Equity income (loss) from unconsolidated JVs		0				0			0	0
Net income (loss)		47,627				55,275			117,005	446,438
SHOP
Segment reporting information, revenues
Gain (loss) on sales of real estate, net				$ 21,000
SHOP | Operating segment
Segment reporting information, revenues
Rental revenues		137,044				126,040			420,067	391,684
Operating expenses		(106,182)				(86,821)			(309,694)	(267,226)
Segment NOI		30,862				39,219			110,373	124,458
Adjustments to NOI		1,378				(35)			(356)	(334)
Adjusted NOI		32,240				39,184			110,017	124,124
Addback adjustments		(1,378)				35			356	334
Interest income		0				0			0	0
Interest expense		(688)				(933)			(2,067)	(6,950)
Depreciation and amortization		(25,166)				(24,884)			(80,797)	(75,657)
General and administrative		0				0			0	0
Transaction costs		0				0			0	0
Recoveries (impairments), net		(5,268)				0			(5,268)	0
Gain (loss) on sales of real estate, net		10,163				(2)			79,340	131
Loss on debt extinguishments		0				0			0	0
Other income (expense), net		0				0			0	0
Income tax benefit (expense)		0				0			0	0
Equity income (loss) from unconsolidated JVs		0				0			0	0
Net income (loss)		9,903				13,400			101,581	41,982
Life science | Operating segment
Segment reporting information, revenues
Rental revenues		98,040				90,174			298,692	262,224
Operating expenses		(23,668)				(19,960)			(68,208)	(56,024)
Segment NOI		74,372				70,214			230,484	206,200
Adjustments to NOI		(1,439)				(785)			(7,423)	(1,211)
Adjusted NOI		72,933				69,429			223,061	204,989
Addback adjustments		1,439				785			7,423	1,211
Interest income		0				0			0	0
Interest expense		(78)				(87)			(240)	(288)
Depreciation and amortization		(34,432)				(30,851)			(105,782)	(95,648)
General and administrative		0				0			0	0
Transaction costs		0				0			0	0
Recoveries (impairments), net		0				0			(7,639)	0
Gain (loss) on sales of real estate, net		80,580				8			80,581	45,922
Loss on debt extinguishments		0				0			0	0
Other income (expense), net		0				0			0	0
Income tax benefit (expense)		0				0			0	0
Equity income (loss) from unconsolidated JVs		0				0			0	0
Net income (loss)		120,442				39,284			197,404	156,186
Medical office | Operating segment
Segment reporting information, revenues
Rental revenues		129,618				119,847			378,798	357,381
Operating expenses		(49,150)				(46,486)			(143,114)	(137,930)
Segment NOI		80,468				73,361			235,684	219,451
Adjustments to NOI		(319)				(578)			(2,383)	(2,304)
Adjusted NOI		80,149				72,783			233,301	217,147
Addback adjustments		319				578			2,383	2,304
Interest income		0				0			0	0
Interest expense		(117)				(126)			(356)	(382)
Depreciation and amortization		(50,294)				(42,047)			(142,229)	(127,261)
General and administrative		0				0			0	0
Transaction costs		0				0			0	0
Recoveries (impairments), net		0				0			0	0
Gain (loss) on sales of real estate, net		3,903				0			3,903	(406)
Loss on debt extinguishments		0				0			0	0
Other income (expense), net		0				0			0	0
Income tax benefit (expense)		0				0			0	0
Equity income (loss) from unconsolidated JVs		0				0			0	0
Net income (loss)		33,960				31,188			97,002	91,402
Other non-reportable segments | Operating segment
Segment reporting information, revenues
Rental revenues		22,597				28,968			85,676	87,524
Operating expenses		(1,367)				(1,137)			(3,932)	(3,475)
Segment NOI		21,230				27,831			81,744	84,049
Adjustments to NOI		(857)				(1,283)			(3,566)	(3,162)
Adjusted NOI		20,373				26,548			78,178	80,887
Addback adjustments		857				1,283			3,566	3,162
Interest income		1,236				11,774			9,048	50,974
Interest expense		0				(618)			(1,469)	(3,541)
Depreciation and amortization		(3,422)				(7,259)			(27,891)	(21,849)
General and administrative		0				0			0	0
Transaction costs		0				0			0	0
Recoveries (impairments), net		0				(25,328)			0	(82,010)
Gain (loss) on sales of real estate, net		223				0			21,074	3,796
Loss on debt extinguishments		0				0			0	0
Other income (expense), net		0				0			(40,567)	50,895
Income tax benefit (expense)		0				0			0	0
Equity income (loss) from unconsolidated JVs		(911)				1,062			(442)	4,571
Net income (loss)		$ 18,356				$ 7,462			$ 41,497	$ 86,885