Organization, Basis of Presentation, and Significant Accounting Policies Organization, Basis of Presentation, and Significant Accounting Policies (Details 4) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Management, development and other fees	$ 3,819	$ 4,960	$ 3,572
Operating Lease, Lease Income	2,297,442	2,319,666	2,280,963
Total revenue	2,301,261	2,324,626	2,284,535
Non-allocated
Disaggregation of Revenue [Line Items]
Total revenue	3,819	4,960	3,572
Established Communities | Operating segment
Disaggregation of Revenue [Line Items]
Total revenue	2,028,317	2,107,288	1,731,570
Other Stabilized Communities | Operating segment
Disaggregation of Revenue [Line Items]
Total revenue	140,173	110,434	238,584
Continuing Operations
Disaggregation of Revenue [Line Items]
Management, development and other fees	13,643	13,612	9,818
Operating Lease, Lease Income	2,242,282	2,236,405	2,084,704
Business interruption insurance proceeds	385	1,441	26
Total revenue	2,256,310	2,251,458	2,094,548
Continuing Operations | Management, Development And Other [Member]
Disaggregation of Revenue [Line Items]
Management, development and other fees	3,819	4,960	3,572
Continuing Operations | Rental and non-rental related income
Disaggregation of Revenue [Line Items]
Management, development and other fees	9,824	8,652	6,246
Continuing Operations | Non-allocated
Disaggregation of Revenue [Line Items]
Management, development and other fees	3,819	4,960	3,572
Operating Lease, Lease Income	0	0	0
Business interruption insurance proceeds	0	0	0
Total revenue	3,819	4,960	3,572
Continuing Operations | Non-allocated | Management, Development And Other [Member]
Disaggregation of Revenue [Line Items]
Management, development and other fees	3,819	4,960	3,572
Continuing Operations | Non-allocated | Rental and non-rental related income
Disaggregation of Revenue [Line Items]
Management, development and other fees	0	0	0
Continuing Operations | Established Communities | Operating segment
Disaggregation of Revenue [Line Items]
Management, development and other fees	6,970	7,028	4,245
Operating Lease, Lease Income	2,021,232	2,099,273	1,727,299
Business interruption insurance proceeds	115	987	26
Total revenue	2,028,317	2,107,288	1,731,570
Continuing Operations | Established Communities | Operating segment | Management, Development And Other [Member]
Disaggregation of Revenue [Line Items]
Management, development and other fees	0	0	0
Continuing Operations | Established Communities | Operating segment | Rental and non-rental related income
Disaggregation of Revenue [Line Items]
Management, development and other fees	6,970	7,028	4,245
Continuing Operations | Other Stabilized Communities | Operating segment
Disaggregation of Revenue [Line Items]
Management, development and other fees	1,790	1,224	1,732
Operating Lease, Lease Income	138,113	108,756	236,852
Business interruption insurance proceeds	270	454	0
Total revenue	140,173	110,434	238,584
Continuing Operations | Other Stabilized Communities | Operating segment | Management, Development And Other [Member]
Disaggregation of Revenue [Line Items]
Management, development and other fees	0	0	0
Continuing Operations | Other Stabilized Communities | Operating segment | Rental and non-rental related income
Disaggregation of Revenue [Line Items]
Management, development and other fees	1,790	1,224	1,732
Continuing Operations | Development/Redevelopment Communities | Operating segment
Disaggregation of Revenue [Line Items]
Management, development and other fees	1,064	400	269
Operating Lease, Lease Income	82,937	28,376	120,553
Business interruption insurance proceeds	0	0	0
Total revenue	84,001	28,776	120,822
Continuing Operations | Development/Redevelopment Communities | Operating segment | Management, Development And Other [Member]
Disaggregation of Revenue [Line Items]
Management, development and other fees	0	0	0
Continuing Operations | Development/Redevelopment Communities | Operating segment | Rental and non-rental related income
Disaggregation of Revenue [Line Items]
Management, development and other fees	$ 1,064	$ 400	$ 269