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
	Jan. 01, 2018 USD ($) community	Nov. 02, 2017 community	Nov. 01, 2017 joint_venture community	Apr. 30, 2018 USD ($) community	Mar. 31, 2018 USD ($)	Jan. 31, 2018 USD ($) community	Dec. 31, 2017 USD ($) joint_venture	Dec. 31, 2018 USD ($) community	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 community	Dec. 31, 2018 USD ($) community	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Deferred revenue													$ 918	$ (13,917)	$ 3,300
Non-cash management contract termination fee													8,724	0	0
Gain on sale of assets, net								$ 216,660	$ 9,833	$ 23,322	$ 43,431		293,246	19,273	7,218
Gain on facility lease termination								$ (13,197)	$ (2,337)	$ (146,467)	$ 0		(162,001)	(14,276)	(11,113)
Revenue													3,449,211
Cash basis payment - operating leases													324,870	$ 365,077	$ 384,104
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
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%				10.00%			10.00%
Number of joint ventures | joint_venture			2				1
Proceeds from sale of joint venture interest					$ 62,300		$ 32,100
Number of communities managed | community			59
Gain on sale of assets, net					$ 41,700		$ 7,200
33 Communities Disposed Of Through Lease Terminations
Business Acquisition [Line Items]
Reduction in capital lease obligations and assets under lease														$ 145,600
33 Communities Disposed Of Through Lease Terminations | HCP, Inc. | Master Lease Transactions
Business Acquisition [Line Items]
Number of communities disposed of | community													33
Capital Lease Obligations								$ 378,300					$ 378,300
Gain on facility lease termination													1,500
Assets under leases								$ 332,800					$ 332,800
Number of communities previously subject to sale leaseback transactions | community													20
20 Of The 33 Communities Disposed Of Through Lease Terminations | HCP, Inc. | Master Lease Transactions
Business Acquisition [Line Items]
Number of communities disposed of | community													20
Gain on sale of assets, net													$ 44,200
37 Communities Disposed Of Through Management Termination | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities disposed of | community		37											31
Non-cash management contract termination fee													$ 8,700
6 Communities Disposed Of Through Management Termination | Forecast | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities disposed of | community												6