Segment Information (Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets
Total assets	$ 23,929,404	$ 24,692,208
Percentage of total assets	100.00%	100.00%
Operating Segments | Triple-net leased properties
Assets
Total assets	$ 5,147,503	$ 6,381,657
Percentage of total assets	21.60%	25.80%
Operating Segments | Senior living operations
Assets
Total assets	$ 10,653,428	$ 10,142,023
Percentage of total assets	44.50%	41.10%
Operating Segments | Office operations
Assets
Total assets	$ 6,709,602	$ 7,173,401
Percentage of total assets	28.00%	29.10%
All Other
Assets
Total assets	$ 1,418,871	$ 995,127
Percentage of total assets	5.90%	4.00%