Segment Reporting - Summary of Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	$ 1,036,874	$ 1,266,133	$ 3,483,951	$ 3,858,484
Total assets	32,541,597		32,541,597		$ 33,380,751
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	819,057	1,039,016	2,820,609	3,175,059
Total assets	26,988,613		26,988,613		27,513,911
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	110,281	110,303	337,601	335,368
Total assets	3,200,439		3,200,439		3,405,388
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenues	107,536	$ 116,814	325,741	$ 348,057
Total assets	$ 2,352,545		$ 2,352,545		$ 2,461,452
Revenue
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage	100.00%	100.00%	100.00%	100.00%
Revenue | United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage	79.00%	82.10%	81.00%	82.30%
Revenue | United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage	10.60%	8.70%	9.70%	8.70%
Revenue | Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage	10.40%	9.20%	9.30%	9.00%
Assets
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage			100.00%		100.00%
Assets | United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage			83.00%		82.40%
Assets | United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage			9.80%		10.20%
Assets | Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage			7.20%		7.40%
Resident fees and services | Revenue | United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage	76.00%		76.00%
Resident fees and services | Revenue | United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage	11.00%		11.00%
Resident fees and services | Revenue | Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Percentage	13.00%		13.00%