Segment Disclosures - Narrative (Details)	3 Months Ended		12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) facility	Dec. 31, 2016 USD ($) facility	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Intersegment sales or transfers					$ 0
Impairment related to goodwill	$ 0	$ 0
Goodwill	47,000,000		$ 47,000,000	$ 42,000,000
Senior housing triple-net
Segment Reporting Information [Line Items]
Number of SH NNN facilities transitioned to RIDEA structure | facility			42	17
Operating segment | Senior housing triple-net
Segment Reporting Information [Line Items]
Goodwill	21,000,000		$ 21,000,000	$ 16,000,000
Operating segment | SHOP
Segment Reporting Information [Line Items]
Goodwill	9,000,000		9,000,000	9,000,000
Operating segment | Medical office
Segment Reporting Information [Line Items]
Goodwill	11,000,000		11,000,000	11,000,000
Operating segment | Other non-reportable segments
Segment Reporting Information [Line Items]
Goodwill	$ 6,000,000		$ 6,000,000	$ 6,000,000