Subsequent Event (Details) $ in Thousands				3 Months Ended		9 Months Ended
	Nov. 01, 2018 community	Jan. 01, 2018 USD ($) community	Nov. 02, 2017 USD ($) community joint_venture	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) joint_venture	Sep. 30, 2016 USD ($)
Subsequent Event [Line Items]
Resident fee revenue | $				$ 922,892	$ 1,042,831	$ 2,873,889	$ 3,158,547
Management fees revenue | $				18,138	15,532	56,474	50,498
Facility operating expenses | $				650,654	704,221	1,967,601	2,113,226
Cash lease payments | $				90,303	96,170	275,506	287,781
32 Communities Disposed Of Through Lease Terminations [Member]
Subsequent Event [Line Items]
Resident fee revenue | $				33,200	35,000	101,300	105,500
Management fees revenue | $				2,500	2,600	7,600	8,200
Facility operating expenses | $				22,400	21,000	64,600	62,900
Cash lease payments | $				$ 11,100	$ 10,300	$ 33,200	$ 30,700
32 Communities Disposed Of Through Lease Terminations [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of communities disposed of			32
37 Communities Disposed Of Through Management Termination [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of communities disposed of			37
Retirement Centers [Member] | 32 Communities Disposed Of Through Lease Terminations [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of communities disposed of			5
Assisted Living [Member] | 32 Communities Disposed Of Through Lease Terminations [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of communities disposed of			27
RIDEA Ventures [Member]
Subsequent Event [Line Items]
Percentage ownership				10.00%		10.00%
Number of joint ventures | joint_venture						3
Master Lease Transactions [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of communities disposed of			2
Number of communities leased			32
Total communities disposed of			34
RIDEA Ventures Restructuring [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of communities acquired			4
Payments to acquire joint ventures | $			$ 239,000
Number of communities management is retained			18
Number of communities expected to be acquired			6
Number of communities expected to be disposed of			69
RIDEA Ventures Restructuring [Member] | 37 Communities Disposed Of Through Management Termination [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of communities disposed of			37
RIDEA Ventures Restructuring [Member] | RIDEA Ventures [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Percentage ownership			10.00%
Number of joint ventures | joint_venture			2
Number of communities managed			59
HCP, Inc. [Member] | Master Lease Transactions [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of communities acquired			2
Payments to acquire joint ventures | $			$ 35,000
Number of communities leased			44
HCP, Inc. [Member] | RIDEA Ventures Restructuring [Member] | RIDEA Ventures [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Proceeds from sale of joint venture interest | $			$ 99,000
Forecast [Member] | Master Lease Transactions [Member]
Subsequent Event [Line Items]
Number of communities disposed of	32
Annual rent reduction | $		$ 5,000
Number of communities with rent reduction		3