Acquisitions, Dispositions and Other Significant Transactions - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) community	Mar. 31, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resident fee revenue | $	$ 906,266	$ 1,016,927
Facility operating expenses | $	632,325	674,542
Cash lease payments | $	$ 89,593	94,604
111 Communities Disposed Of By Sales And Lease Terminations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community	111
Resident fee revenue | $	$ 2,200	107,600
Facility operating expenses | $	$ 2,100	81,000
Cash lease payments | $		$ 27,800
6 Communities Disposed Of By Sales [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community	6
105 Communities Disposed Of By Lease Terminations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community	105
Assisted Living [Member] | 111 Communities Disposed Of By Sales And Lease Terminations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community	88
Retirement Centers [Member] | 111 Communities Disposed Of By Sales And Lease Terminations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community	10
CCRCs Rental [Member] | 111 Communities Disposed Of By Sales And Lease Terminations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of | community	13