Concentration of Credit Risk - Schedule of Concentration Risk (Details)	1 Months Ended	3 Months Ended				9 Months Ended		12 Months Ended
	Mar. 31, 2017 property	Sep. 30, 2018	Jun. 30, 2018 facility	Dec. 31, 2017 facility	Sep. 30, 2017 facility	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Total Assets | Brookdale
Concentration Risk [Line Items]
Concentration risk (as a percent)						8.00%		10.00%
Revenue | Brookdale
Concentration Risk [Line Items]
Concentration risk (as a percent)		5.00%			8.00%	6.00%	10.00%
Senior housing triple-net
Concentration Risk [Line Items]
Number of properties disposed	64		2	2	2
Senior housing triple-net | Total Assets | Brookdale
Concentration Risk [Line Items]
Concentration risk (as a percent)						34.00%		39.00%
Senior housing triple-net | Revenue | Brookdale
Concentration Risk [Line Items]
Concentration risk (as a percent)		37.00%			48.00%	40.00%	53.00%