Segment Disclosures - Summary Information for the Reportable Segments (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended								12 Months Ended
	Mar. 31, 2017	Jan. 31, 2017	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment reporting information, revenues
Rental estate revenues											$ 1,836,283	$ 1,792,141	$ 2,040,486
Operating expenses											(705,038)	(666,251)	(738,399)
NOI											1,131,245	1,125,890	1,302,087
Adjustments to NOI											(11,904)	38,410	(19,764)
Adjusted NOI											1,119,341	1,164,300	1,282,323
Addback adjustments											11,904	(38,410)	19,764
Interest income											10,406	56,237	88,808
Interest expense											(266,343)	(307,716)	(464,403)
Depreciation and amortization											(549,499)	(534,726)	(568,108)
General and administrative											(96,702)	(88,772)	(103,611)
Transaction costs											(10,772)	(7,963)	(9,821)
Recoveries (impairments), net											(55,260)	(166,384)	0
Gain (loss) on sales of real estate, net				$ 95,000	$ 25,000						925,985	356,641	164,698
Loss on debt extinguishment											(44,162)	(54,227)	(46,020)
Other income (expense), net											13,316	31,420	3,654
Income tax benefit (expense)											17,854	1,333	(4,473)
Equity income (loss) from unconsolidated joint ventures											(2,594)	10,901	11,360
Discontinued operations											0	0	265,755
Net income (loss)			$ 834,383	$ 102,926	$ 92,928	$ 43,237	$ (57,924)	$ (5,720)	$ 22,101	$ 464,177	1,073,474	422,634	639,926
Corporate Non-segment
Segment reporting information, revenues
Rental estate revenues											0	0	0
Operating expenses											0	0	0
NOI											0	0	0
Adjustments to NOI											0	0	0
Adjusted NOI											0	0	0
Addback adjustments											0	0	0
Interest income											0	0	0
Interest expense											(258,955)	(292,169)	(407,754)
Depreciation and amortization											0	0	0
General and administrative											(96,702)	(88,772)	(103,611)
Transaction costs											(10,772)	(7,963)	(9,821)
Recoveries (impairments), net											0	0
Gain (loss) on sales of real estate, net											0	0	0
Loss on debt extinguishment											(44,162)	(54,227)	(46,020)
Other income (expense), net											3,711	(19,475)	3,654
Income tax benefit (expense)											17,854	1,333	(4,473)
Equity income (loss) from unconsolidated joint ventures											0	0	0
Discontinued operations													265,755
Net income (loss)											(389,026)	(461,273)	(302,270)
Senior housing triple-net
Segment reporting information, revenues
Recoveries (impairments), net												(23,000)
Gain (loss) on sales of real estate, net	$ 170,000
Senior housing triple-net | Operating segment
Segment reporting information, revenues
Rental estate revenues											276,091	313,547	423,118
Operating expenses											(3,618)	(3,819)	(6,710)
NOI											272,473	309,728	416,408
Adjustments to NOI											2,127	17,098	(7,566)
Adjusted NOI											274,600	326,826	408,842
Addback adjustments											(2,127)	(17,098)	7,566
Interest income											0	0	0
Interest expense											(2,404)	(2,518)	(9,499)
Depreciation and amortization											(79,605)	(103,820)	(136,146)
General and administrative											0	0	0
Transaction costs											0	0	0
Recoveries (impairments), net											0	(22,590)
Gain (loss) on sales of real estate, net											641	280,349	48,744
Loss on debt extinguishment											0	0	0
Other income (expense), net											0	0	0
Income tax benefit (expense)											0	0	0
Equity income (loss) from unconsolidated joint ventures											0	0	0
Discontinued operations													0
Net income (loss)											191,105	461,149	319,507
SHOP
Segment reporting information, revenues
Recoveries (impairments), net			$ (33,000)								(52,000)
Gain (loss) on sales of real estate, net						$ 21,000
SHOP | Operating segment
Segment reporting information, revenues
Rental estate revenues											547,976	525,473	686,822
Operating expenses											(414,312)	(396,491)	(480,870)
NOI											133,664	128,982	205,952
Adjustments to NOI											2,875	33,227	(2,686)
Adjusted NOI											136,539	162,209	203,266
Addback adjustments											(2,875)	(33,227)	2,686
Interest income											0	0	0
Interest expense											(2,725)	(7,920)	(29,745)
Depreciation and amortization											(104,405)	(103,162)	(108,806)
General and administrative											0	0	0
Transaction costs											0	0	0
Recoveries (impairments), net											(44,343)	0
Gain (loss) on sales of real estate, net											93,977	17,485	675
Loss on debt extinguishment											0	0	0
Other income (expense), net											0	0	0
Income tax benefit (expense)											0	0	0
Equity income (loss) from unconsolidated joint ventures											0	0	0
Discontinued operations													0
Net income (loss)											76,168	35,385	68,076
Life science
Segment reporting information, revenues
Gain (loss) on sales of real estate, net		$ 45,000
Life science | Operating segment
Segment reporting information, revenues
Rental estate revenues											395,064	358,816	358,537
Operating expenses											(91,742)	(78,001)	(72,478)
NOI											303,322	280,815	286,059
Adjustments to NOI											(9,589)	(4,517)	(2,954)
Adjusted NOI											293,733	276,298	283,105
Addback adjustments											9,589	4,517	2,954
Interest income											0	0	0
Interest expense											(316)	(373)	(2,357)
Depreciation and amortization											(140,480)	(128,864)	(130,829)
General and administrative											0	0	0
Transaction costs											0	0	0
Recoveries (impairments), net											(7,639)	0
Gain (loss) on sales of real estate, net											806,184	45,916	49,042
Loss on debt extinguishment											0	0	0
Other income (expense), net											0	0	0
Income tax benefit (expense)											0	0	0
Equity income (loss) from unconsolidated joint ventures											0	0	0
Discontinued operations													0
Net income (loss)											961,071	197,494	201,915
Medical office
Segment reporting information, revenues
Gain (loss) on sales of real estate, net												41,000
Medical office | Operating segment
Segment reporting information, revenues
Rental estate revenues											509,019	477,459	446,280
Operating expenses											(189,859)	(183,197)	(173,687)
NOI											319,160	294,262	272,593
Adjustments to NOI											(2,899)	(2,952)	(3,536)
Adjusted NOI											316,261	291,310	269,057
Addback adjustments											2,899	2,952	3,536
Interest income											0	0	0
Interest expense											(474)	(506)	(5,895)
Depreciation and amortization											(193,710)	(169,795)	(161,790)
General and administrative											0	0	0
Transaction costs											0	0	0
Recoveries (impairments), net											0	0
Gain (loss) on sales of real estate, net											4,428	9,095	8,333
Loss on debt extinguishment											0	0	0
Other income (expense), net											0	0	0
Income tax benefit (expense)											0	0	0
Equity income (loss) from unconsolidated joint ventures											0	0	0
Discontinued operations													0
Net income (loss)											129,404	133,056	113,241
Other non-reportable segments | Operating segment
Segment reporting information, revenues
Rental estate revenues											108,133	116,846	125,729
Operating expenses											(5,507)	(4,743)	(4,654)
NOI											102,626	112,103	121,075
Adjustments to NOI											(4,418)	(4,446)	(3,022)
Adjusted NOI											98,208	107,657	118,053
Addback adjustments											4,418	4,446	3,022
Interest income											10,406	56,237	88,808
Interest expense											(1,469)	(4,230)	(9,153)
Depreciation and amortization											(31,299)	(29,085)	(30,537)
General and administrative											0	0	0
Transaction costs											0	0	0
Recoveries (impairments), net											(3,278)	(143,794)
Gain (loss) on sales of real estate, net											20,755	3,796	57,904
Loss on debt extinguishment											0	0	0
Other income (expense), net											9,605	50,895	0
Income tax benefit (expense)											0	0	0
Equity income (loss) from unconsolidated joint ventures											(2,594)	10,901	11,360
Discontinued operations													0
Net income (loss)											$ 104,752	$ 56,823	$ 239,457