Acquisitions, Dispositions and Other Significant Transactions - Additional Information (Details) $ in Thousands	3 Months Ended		9 Months Ended		15 Months Ended	21 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) community	Sep. 30, 2017 USD ($)	Sep. 30, 2018 community	Sep. 30, 2018 community
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue	$ 840,179		$ 2,642,414
Cash lease payments	73,969	$ 90,303	250,677	$ 275,506
6 Communities Disposed Of By Sales
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community						6
171 Communities Disposed Of By Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community						171
104 Communities Disposed Of Through Sale And Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community					104
Cash lease payments	4,800	30,500
177 Communities Disposed Of By Sales And Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community						177
Cash lease payments			55,200	115,300
Assisted Living
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue	483,125		$ 1,537,432
Assisted Living | 177 Communities Disposed Of By Sales And Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community			143
Retirement Centers
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue	144,631		$ 462,321
Retirement Centers | 177 Communities Disposed Of By Sales And Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community			20
CCRCs Rental
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue	104,147		$ 314,012
CCRCs Rental | 177 Communities Disposed Of By Sales And Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community			14
Resident fees
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue	840,179	922,892	$ 2,642,414	2,873,889
Resident fees | 104 Communities Disposed Of Through Sale And Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue	15,000	106,900
Resident fees | 177 Communities Disposed Of By Sales And Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue			164,300	408,800
Facility operating expense
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Costs of services	607,076	650,654	1,866,477	1,967,601
Facility operating expense | 104 Communities Disposed Of Through Sale And Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Costs of services	$ 11,200	$ 75,600
Facility operating expense | 177 Communities Disposed Of By Sales And Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Costs of services			$ 110,700	$ 287,700
HCP Transactions
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities acquired | community			6
HCP Transactions | Assisted Living
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities acquired | community			3
HCP Transactions | Retirement Centers
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities acquired | community			2
HCP Transactions | CCRCs Rental
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities acquired | community			1