Acquisitions, Dispositions and Other Significant Transactions - Revenue of Disposal Groups (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash lease payments			$ 324,870
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	$ 34,575	$ 115,566	450,092
Facility operating expense	33,005	102,693	334,605
Cash lease payments	4,696	9,011	91,169
Independent Living | 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	0	0	81,279
Facility operating expense	0	0	48,161
Assisted Living and Memory Care | 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	14,080	50,775	284,627
Facility operating expense	13,008	43,880	211,546
CCRCs | 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	20,495	64,791	84,186
Facility operating expense	$ 19,997	$ 58,813	$ 74,898