Acquisitions, Dispositions and Other Significant Transactions - Additional Information (Details) $ in Thousands		1 Months Ended	3 Months Ended		12 Months Ended
	Nov. 01, 2016 community	Jan. 31, 2017 community	Dec. 31, 2017 USD ($) community	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) community	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 29, 2017 community
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of assets | $				$ 46,700
Resident fee revenue | $					$ 3,780,140	$ 4,168,621	$ 4,177,127
Facility operating expense | $					2,602,155	2,799,402	2,788,862
Cash basis payment | $					365,077	384,104	372,148
Loss on termination | $					14,276	11,113	76,143
Assets held for sale | $			$ 106,435		$ 106,435	97,843	110,600
CCRCs-Rental
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of			7
165 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					165
Resident fee revenue | $					$ 172,600	543,300	572,100
Facility operating expense | $					135,000	413,100	434,900
Cash basis payment | $					$ 39,300	131,400	$ 129,500
Termination Of Triple Net Leases
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of	97
Termination Of Triple Net Leases, 33 Communities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of	33
Termination Of 8 Triple Net Leases
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of	8	1
Termination Of 8 Triple Net Leases | Assisted Living
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of					6
Termination Of 8 Triple Net Leases | Retirement Centers
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of					1
Termination Of 8 Triple Net Leases | CCRCs-Rental
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of					1
Termination Of 25 Triple Net Leases
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of	25				25
Three Communities [Member] | 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]
Number of communities disposed of					3
Proceeds from sale of assets | $					$ 8,200
15 Communities Held For Sale | 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]
Resident fee revenue | $					49,500	51,500
Facility operating expense | $					$ 43,800	44,600
Number of communities classified as held for sale					15
15 Communities Held For Sale | Long-term Debt | 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]
Long term mortgage debt | $			$ 30,100		$ 30,100	$ 60,500
15 Communities Held For Sale | Assisted Living | 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]
Additional communities disposed of in agreement					12
15 Communities Held For Sale | CCRCs-Rental | 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]
Additional communities disposed of in agreement					3
14 Communities Disposed Of By Lease Terminations | 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]
Number of community leases terminated					17
14 Communities Disposed Of By Lease Terminations | Assisted Living | 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]
Additional communities disposed of in agreement					14
14 Communities Disposed Of By Lease Terminations | Retirement Centers | 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]
Additional communities disposed of in agreement					2
14 Communities Disposed Of By Lease Terminations | CCRCs-Rental | 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]
Additional communities disposed of in agreement					1
HCP, Inc.
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities contributed to joint venture	4
Senior Housing Communities | Joint Venture | Blackstone Venture
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities acquired								64