Segment Disclosures - Revenues and Assets by Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Disclosure
Total revenues	$ 443,259	$ 454,023	$ 458,928	$ 492,168	$ 539,950	$ 530,555	$ 538,332	$ 520,457	$ 1,848,378	$ 2,129,294	$ 1,940,489
Total assets	14,088,461				15,759,265				14,088,461	15,759,265	21,449,849
Assets held for sale and discontinued operations, net	417,014				927,866				417,014	927,866	5,654,326
Operating segment
Segment Disclosure
Gross assets	14,051,070				14,692,941				14,051,070	14,692,941	14,801,775
Accumulated depreciation and amortization	(2,919,278)				(2,900,060)				(2,919,278)	(2,900,060)	(2,704,425)
Total assets	11,131,792				11,792,881				11,131,792	11,792,881	12,097,350
Operating segment | Senior housing triple-net
Segment Disclosure
Total revenues									313,547	423,118	428,269
Gross assets	3,515,400				3,871,720				3,515,400	3,871,720	5,092,443
Operating segment | SHOP
Segment Disclosure
Total revenues									525,473	686,822	518,264
Gross assets	2,392,130				3,135,115				2,392,130	3,135,115	2,684,675
Operating segment | Life science
Segment Disclosure
Total revenues									358,816	358,537	342,984
Gross assets	4,154,372				3,961,623				4,154,372	3,961,623	3,613,726
Operating segment | Medical office
Segment Disclosure
Total revenues									477,459	446,280	415,351
Gross assets	3,989,168				3,724,483				3,989,168	3,724,483	3,410,931
Operating segment | Other non-reportable segments
Segment Disclosure
Total revenues									173,083	214,537	235,621
Total assets	1,904,433				2,255,712				1,904,433	2,255,712	2,392,823
Other non-segment
Segment Disclosure
Total assets	$ 635,222				$ 782,806				$ 635,222	$ 782,806	$ 1,305,350