Acquisitions, Dispositions and Other Significant Transactions - Revenue of Disposal Groups (Details) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resident fees	$ 1,008,949	$ 1,120,062	$ 3,070,450	$ 3,462,496
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	103	63,996	12,385	313,839
Facility operating expense	103	47,555	10,204	218,563
Cash facility lease payments	0	13,111	1,451	80,046
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	14,099	0	74,970
Facility operating expense	0	8,588	0	44,256
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	103	45,496	12,385	223,763
Facility operating expense	103	35,182	10,204	160,606
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	4,401	0	15,106
Facility operating expense	$ 0	$ 3,785	$ 0	$ 13,701