Acquisitions, Dispositions and Other Significant Transactions - 2017 HCP Master Lease Transaction (Details) $ in Millions				1 Months Ended	12 Months Ended
	Nov. 01, 2018 community	Jan. 01, 2018 USD ($) community	Nov. 02, 2017 USD ($) community joint_venture	Dec. 31, 2017 USD ($) joint_venture	Dec. 31, 2017 joint_venture
RIDEA Ventures
Business Acquisition [Line Items]
Ownership Percentage				10.00%	10.00%
Number of joint ventures | joint_venture					2
Master Lease Transactions
Business Acquisition [Line Items]
Total communities disposed of			35
RIDEA Ventures Restructuring
Business Acquisition [Line Items]
Number of communities acquired			4
Payments to acquire joint ventures | $			$ 239.5
Number of communities management is retained			18
RIDEA Ventures Restructuring | 37 Communities Disposed Of Through Management Termination
Business Acquisition [Line Items]
Number of communities disposed of			37
RIDEA Ventures Restructuring | RIDEA Ventures
Business Acquisition [Line Items]
Ownership Percentage			10.00%
Number of joint ventures | joint_venture			2	2
Proceeds from sale of joint venture interest | $			$ 94.7
Number of communities managed			59
HCP, Inc. | Master Lease Transactions
Business Acquisition [Line Items]
Number of communities acquired			2
Payments to acquire joint ventures | $			$ 35.4
Number of communities leased			43
HCP, Inc. | RIDEA Ventures Restructuring | RIDEA Ventures
Business Acquisition [Line Items]
Number of joint ventures | joint_venture				1
Proceeds from sale of joint venture interest | $				$ 32.1
Forecast | Master Lease Transactions
Business Acquisition [Line Items]
Number of communities disposed of	33
Subsequent event | Master Lease Transactions
Business Acquisition [Line Items]
Annual rent reduction | $		$ 2.5
Number of communities with rent reduction		2