Acquisitions, Dispositions and Other Significant Transactions (Details) $ in Thousands		3 Months Ended				6 Months Ended	9 Months Ended		12 Months Ended	21 Months Ended
	Nov. 01, 2016 community	Dec. 31, 2017 community	Sep. 30, 2017 USD ($) community	Dec. 31, 2016 community	Sep. 30, 2016 USD ($)	Jun. 30, 2016 community	Sep. 30, 2017 USD ($) community	Sep. 30, 2016 USD ($)	Dec. 31, 2016 community	Sep. 30, 2017 USD ($) community
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resident fee revenue | $			$ 922,892		$ 1,042,831		$ 2,873,889	$ 3,158,547
Facility operating expenses | $			650,654		704,221		1,967,601	2,113,226
Cash lease payments | $			90,303		96,170		275,506	287,781
Loss on facility lease termination | $			$ 4,938		0		$ 11,306	0
CCRCs Rental [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of				7
139 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			136			3	139			139
Resident fee revenue | $			$ 4,000		115,100		$ 96,600	361,100
Facility operating expenses | $			3,300		87,400		74,400	272,600
Cash lease payments | $			$ 900		27,500		$ 26,800	82,400
Termination Of Triple Net Leases [Member]
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 [Member]
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 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of	8
Termination Of 8 Triple Net Leases [Member] | Assisted Living [Member]
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 [Member] | Retirement Centers [Member]
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 [Member] | CCRCs Rental [Member]
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 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of	25		25				25
Resident fee revenue | $			$ 18,000		18,100		$ 54,900	54,600
Facility operating expenses | $			14,800		14,600		44,700	44,000
Cash lease payments | $			$ 2,600		4,900		$ 8,100	14,700
Termination Of 25 Triple Net Leases, 2 Communities Terminated [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of			2
16 Communities Held For Sale [Member] | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of			1				3
Number of communities classified as held for sale									16
15 Communities Held For Sale [Member] | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resident fee revenue | $			$ 12,200		12,800		$ 37,600	39,000
Facility operating expenses | $			10,900		$ 11,000		$ 33,200	$ 33,700
Number of communities classified as held for sale							15
Assets held for sale | $			106,400				$ 106,400			$ 106,400
15 Communities Held For Sale [Member] | Long-term Debt [Member] | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long term mortgage debt | $			$ 50,400				$ 50,400			$ 50,400
15 Communities Held For Sale [Member] | Assisted Living [Member] | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
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 [Member] | CCRCs Rental [Member] | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
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 [Member] | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of community leases terminated							14
14 Communities Disposed Of By Lease Terminations [Member] | Assisted Living [Member] | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Additional communities disposed of in agreement							12
14 Communities Disposed Of By Lease Terminations [Member] | Retirement Centers [Member] | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Additional communities disposed of in agreement							1
14 Communities Disposed Of By Lease Terminations [Member] | CCRCs Rental [Member] | Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Additional communities disposed of in agreement							1
Blackstone Venture [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities acquired	64
HCP, Inc. [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities contributed to joint venture	4			4
HCP, Inc. [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage ownership	10.00%
Forecast [Member] | Termination Of 25 Triple Net Leases [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of communities disposed of		23