Acquisitions, Dispositions and Other Significant Transactions - 2017 HCP Master Lease Transactions 2 (Details) $ in Thousands			1 Months Ended	3 Months Ended	12 Months Ended
	Nov. 01, 2018 community	Nov. 02, 2017 USD ($) community joint_venture	Dec. 31, 2017 USD ($) joint_venture	Dec. 31, 2017 USD ($) community	Dec. 31, 2018 community	Dec. 31, 2017 USD ($) community joint_venture	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Gain on sale of assets, net						$ 19,273	$ 7,218	$ 1,270
Resident fee revenue						3,780,140	4,168,621	4,177,127
Management fees						75,845	70,762	60,183
Facility operating expense						2,602,155	2,799,402	2,788,862
Cash basis payment						365,077	384,104	$ 372,148
Master Lease Transactions
Business Acquisition [Line Items]
Number of communities expected to be acquired | community		6
Deferred revenue liability			$ 9,700	$ 9,700		$ 9,700
Forecast | Master Lease Transactions
Business Acquisition [Line Items]
Number of communities disposed of | community	33
37 Communities Disposed Of Through Management Termination | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities disposed of | community		37
33 Communities Disposed Of Through Lease Terminations
Business Acquisition [Line Items]
Number of communities disposed of | community						33
Decrease in capital lease obligations						$ 145,600
Carrying value			395,000	395,000		395,000
Assets under leases			347,000	347,000		347,000
Amount exceeding carrying value of assets under leases			$ 48,000	$ 48,000		$ 48,000
Number of communities | community						20
Resident fee revenue						$ 143,900	151,700
Management fees						10,100	11,800
Facility operating expense						94,500	92,600
Cash basis payment						$ 48,300	$ 44,800
HCP, Inc. | Master Lease Transactions
Business Acquisition [Line Items]
Number of communities expected to be disposed of | community		70
RIDEA Ventures
Business Acquisition [Line Items]
Number of joint ventures | joint_venture						2
RIDEA Ventures | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of joint ventures | joint_venture		2	2
Proceeds from sale of joint venture interest		$ 94,700
RIDEA Ventures | HCP, Inc. | RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of joint ventures | joint_venture			1
Proceeds from sale of joint venture interest			$ 32,100
Gain on sale of assets, net			$ 7,200
Capital and Financing Lease Obligations | Forecast
Business Acquisition [Line Items]
Number of communities | community					20
Retirement Centers | 33 Communities Disposed Of Through Lease Terminations
Business Acquisition [Line Items]
Number of communities disposed of | community						5
Assisted Living | 33 Communities Disposed Of Through Lease Terminations
Business Acquisition [Line Items]
Number of communities disposed of | community						27
CCRCs-Rental
Business Acquisition [Line Items]
Number of communities disposed of | community				7
CCRCs-Rental | 33 Communities Disposed Of Through Lease Terminations
Business Acquisition [Line Items]
Number of communities disposed of | community						1