Acquisitions, Dispositions and Other Significant Transactions - Additional Information (Details) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended	15 Months Ended	18 Months Ended
	Jun. 30, 2019 USD ($) community	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($) community	Jun. 30, 2019 USD ($) community	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) community	Jun. 30, 2019 USD ($) community	Jun. 30, 2019 USD ($) community
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of unconsolidated joint ventures, interest sold				5
Number of communities, acquired, previously leased or managed								6
Operating and financing leases, number of communities	335			335			335	335
Number of communities disposed through sales or termination of lease							124
Gain on sale of assets, net | $	$ 2,846	$ 23,322		$ 2,144	$ 66,753
Assets held for sale | $	$ 46,307			$ 46,307		$ 93,117	$ 46,307	$ 46,307
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								30
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								97
118 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								127
Sale of 3 communities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of			3
Net cash proceeds | $			$ 12,800
Mortgage notes payable
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payment for debt extinguishment or debt prepayment cost | $						$ 174,000
Current Property Ownership Status
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities owned				336
Operating and financing leases, number of communities	335			335			335	335
Number of communities managed				17
Number of communities managed by third party	121			121			121	121
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Eight Communities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of				8
Net cash proceeds | $				$ 44,100
Gain on sale of assets, net | $	$ 1,600			$ 900
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Five 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				5
Assets held for sale | $	46,300			$ 46,300			$ 46,300	$ 46,300
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]
Number of communities disposed of						22
Net cash proceeds | $						$ 380,700
Gain on sale of assets, net | $					$ 1,900	188,600
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Mortgage notes payable
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Mortgage debt | $	18,500			18,500		$ 31,200	18,500	18,500
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations | Mortgage notes payable | Five Communities Held For Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Mortgage debt | $	$ 18,500			$ 18,500			$ 18,500	$ 18,500