Segment Information (Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets
Total assets	$ 23,166,600	$ 22,261,918
Percentage of total assets	100.00%	100.00%
Operating Segments | Triple-net leased properties
Assets
Total assets	$ 7,627,792	$ 7,996,645
Percentage of total assets	32.90%	35.90%
Operating Segments | Senior living operations
Assets
Total assets	$ 7,826,262	$ 8,022,206
Percentage of total assets	33.80%	36.00%
Operating Segments | Office operations
Assets
Total assets	$ 6,614,454	$ 5,209,751
Percentage of total assets	28.60%	23.40%
All Other
Assets
Total assets	$ 1,098,092	$ 1,033,316
Percentage of total assets	4.70%	4.70%