Acquisitions, Dispositions and Other Significant Transactions - Revenue of Disposal Groups (Details) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resident fees	$ 1,019,457	$ 1,155,200	$ 2,061,501	$ 2,342,434
Communities Disposed Of Through Sale And Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resident fees	2,176	119,605	12,282	249,843
Facility operating expense	1,562	81,729	10,100	171,008
Cash facility lease payments	306	32,228	1,451	66,935
Communities Disposed Of Through Sale And Lease Terminations | Independent Living
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resident fees	0	29,241	0	60,871
Facility operating expense	0	17,016	0	35,668
Communities Disposed Of Through Sale And Lease Terminations | Assisted Living and Memory Care
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resident fees	2,176	86,151	12,282	178,267
Facility operating expense	1,562	60,854	10,100	125,423
Communities Disposed Of Through Sale And Lease Terminations | CCRCs
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resident fees	0	4,213	0	10,705
Facility operating expense	$ 0	$ 3,859	$ 0	$ 9,917