Acquisitions - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($) Bed Property	Jun. 30, 2016 USD ($) Bed Property
Business Acquisition [Line Items]
Number of land parcels | Property	5
Total purchase price	$ 23.1
Total cash consideration	$ 17.0
Number of properties owned | Property	160
Number of beds | Bed	99,000
Wholly-owned properties
Business Acquisition [Line Items]
Total purchase price	$ 158.5
Total cash consideration	$ 158.0
Number of beds | Bed	982
Series of Individually Immaterial Business Acquisitions | In-Process Development Properties
Business Acquisition [Line Items]
Total purchase price		$ 66.0
Number of properties owned | Property		3
Number of beds | Bed		1,593
Mortgage debt assumed		$ 10.0