Acquisitions, Dispositions and Other Significant Transactions - 2016 HCP Agreements (Details) $ in Thousands			3 Months Ended					12 Months Ended
	Mar. 29, 2017 community	Nov. 01, 2016 community	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2016 community	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) community	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Gain on sale of assets, net | $			$ 216,660	$ 9,833	$ 23,322	$ 43,431		$ 293,246	$ 19,273	$ 7,218
Termination Of Triple Net Leases
Business Acquisition [Line Items]
Number of communities disposed of		97
Termination Of Triple Net Leases, 33 Communities
Business Acquisition [Line Items]
Number of communities disposed of		33
Termination of 8 triple net leases
Business Acquisition [Line Items]
Number of communities disposed of		8
Ownership Percentage		10.00%
Termination Of 7 Triple Net Leases
Business Acquisition [Line Items]
Number of communities disposed of							7
Termination Of 25 Triple Net Leases
Business Acquisition [Line Items]
Number of communities disposed of		25
Sale Of 21 Communities
Business Acquisition [Line Items]
Number of communities disposed of									21
Financing leases | $									$ 145,300
Finance lease obligations | $									156,700
Gain on sale of assets, net | $									$ 11,400
HCP, Inc.
Business Acquisition [Line Items]
Number communities contributed to joint venture		4
Joint Venture | Blackstone Venture | Senior Housing Communities
Business Acquisition [Line Items]
Number of communities acquired	64