Acquisitions, Dispositions and Other Significant Transactions - HCP Master Lease Transaction and RIDEA Ventures Restructuring (Details) $ in Thousands				1 Months Ended				3 Months Ended								12 Months Ended
	Apr. 30, 2018 community	Jan. 01, 2018 USD ($) community	Nov. 01, 2017 joint_venture community	Apr. 30, 2018 USD ($) community	Mar. 31, 2018 USD ($)	Jan. 31, 2018 USD ($) community	Dec. 31, 2017 USD ($) joint_venture	Dec. 31, 2019 USD ($) lease community	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) lease community	Dec. 31, 2018 USD ($) community	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Number of communities leased | lease								242								242
Ownership Percentage								50.00%								50.00%
Gain (loss) on sale of assets, net								$ 4,522	$ 579	$ 2,846	$ (702)	$ 216,660	$ 9,833	$ 23,322	$ 43,431	$ 7,245	$ 293,246	$ 19,273
Non-cash management contract termination fee																969	8,724	0
Gain on facility lease termination								$ 1,382	$ 0	$ 1,797	$ 209	$ 13,197	$ 2,337	$ 146,467	$ 0	(3,388)	$ (162,001)	(14,276)
Master Lease Transactions
Business Acquisition [Line Items]
Annual rent reduction		$ 2,500
Number of communities with rent reduction | community		2
RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities management is retained | community				18
Reduction in lease liabilities																(9,700)
Deferred revenue																$ 9,700
HCP, Inc.
Business Acquisition [Line Items]
Number of communities acquired | community	5
HCP, Inc. | Master Lease Transactions
Business Acquisition [Line Items]
Number of communities acquired | community																	2
Payment to acquire leased assets																	$ 35,400
Number of communities leased | community								43								43
Reduction in capital lease obligations and assets under lease																		$ (145,600)
HCP, Inc. | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities acquired | community				3		1
Payments to acquire asset from joint venture				$ 207,400		$ 32,100
RIDEA Ventures | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Ownership Percentage												10.00%					10.00%
Number of joint ventures | joint_venture			2				1
Proceeds from sale of joint venture interest					$ 62,300		$ 32,100
Gain (loss) on sale of assets, net					$ 41,700		$ 7,200
Number of communities managed | community			59
33 Communities Disposed Of Through Lease Terminations | HCP, Inc. | Master Lease Transactions
Business Acquisition [Line Items]
Number of communities disposed of | community																	33
Assets under leases																	$ 332,800
Capital lease obligations												$ 378,300					$ 378,300
Number of communities previously subject to sale leaseback transactions | community																	20
Gain on facility lease termination																	$ 1,500
37 Communities Disposed Of Through Operations and or Management Termination | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities disposed of | community																37
37 Communities Disposed Of Through Management Agreement | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities disposed of | community																37
37 Communities Disposed Of Through Management Termination | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Non-cash management contract termination fee																$ 9,700
20 Of The 33 Communities Disposed Of Through Lease Terminations | HCP, Inc. | Master Lease Transactions
Business Acquisition [Line Items]
Gain (loss) on sale of assets, net																	$ 44,200