Acquisitions, Dispositions and Other Significant Transactions - Revenue of Disposal Groups (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resident fees	$ 4,057,088	$ 4,531,426	$ 4,747,116
Cash lease payments		324,870	365,077
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	54,080	390,533	742,360
Facility operating expense	52,377	286,536	529,578
Cash lease payments	1,694	84,041	178,187
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	81,280	152,190
Facility operating expense	0	48,154	90,134
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	20,891	256,038	476,677
Facility operating expense	18,249	187,411	336,314
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	33,189	53,215	113,493
Facility operating expense	$ 34,128	$ 50,971	$ 103,130