Dispositions and Acquisitions - Additional Information (Detail)	3 Months Ended	9 Months Ended
	Sep. 30, 2018 Facility Bed	Sep. 30, 2018 USD ($) Bed	Sep. 30, 2017 USD ($)
Business Acquisition [Line Items]
Acquisition, cash paid | $		$ 108,000,000	$ 20,000,000
Aggregate cash proceeds from divestiture of businesses | $			$ 0
The Limes
Business Acquisition [Line Items]
Aggregate cash proceeds from divestiture of businesses | $		$ 14,000,000
Number of beds | Bed		18
Gulfport Behavioral Health System
Business Acquisition [Line Items]
Number of beds | Bed		109
Danshell Group | Located in U.K.
Business Acquisition [Line Items]
Number of beds | Bed	288
Number of behavioral health care facilities | Facility	25