Acquisitions, Dispositions and Other Significant Transactions - Additional Information (Details) $ in Thousands	3 Months Ended								12 Months Ended			21 Months Ended	36 Months Ended
	Dec. 31, 2019 USD ($) community	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) community	Dec. 31, 2018 USD ($) community	Dec. 31, 2017 USD ($) community	Sep. 30, 2019 community	Dec. 31, 2019 USD ($) community
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of unconsolidated ventures interest sold												8
Number of communities leased	333								333				333
Assets held for sale | $	$ 42,671				$ 93,117				$ 42,671	$ 93,117			$ 42,671
Gain (loss) on sale of assets, net | $	$ 4,522	$ 579	$ 2,846	$ (702)	216,660	$ 9,833	$ 23,322	$ 43,431	$ 7,245	$ 293,246	$ 19,273
Communities Disposed Of Through Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of											3		39
Communities Disposed Of Through Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of									10	89	105		204
243 Communities Disposed Of Through Lease Terminations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of													243
Communities Acquired Previously Leased Or Managed
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities acquired									6
Current Property Ownership Status
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities owned	330								330				330
Number of communities leased	333								333				333
Number of communities managed									17
Number of communities managed by third party	83								83				83
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Communities Disposed Of Through Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of									14	22
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Three Communities Held For Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities classified as held for sale									3
Assets held for sale | $	$ 42,700								$ 42,700				$ 42,700
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Sale of 3 communities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net cash proceeds | $											$ 8,200
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | CCRC Venture
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities classified as held for sale									2
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Assisted Living and Memory Care
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities classified as held for sale									1
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Sale of 14 Communities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net cash proceeds | $									$ 85,400
Gain (loss) on sale of assets, net | $									5,500
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Sale Of 22 Communities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net cash proceeds | $										$ 380,700
Gain (loss) on sale of assets, net | $										188,600
Mortgage notes payable
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payment for extinguishment of debt and prepayment penalties | $									5,100	174,000
Mortgage notes payable | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Mortgage debt | $	28,900				$ 31,200				28,900	$ 31,200			28,900
Mortgage notes payable | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Three Communities Held For Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Mortgage debt | $	$ 28,900								$ 28,900				$ 28,900