Revenue - Schedule of U.S. Revenue Attributed to Each Category (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue	$ 743,547	$ 760,916	$ 765,738	$ 742,241	$ 724,512	$ 716,714	$ 715,896	$ 679,194	$ 3,012,442	$ 2,836,316	$ 2,810,914
U.S. Facilities [Member]
Disaggregation of Revenue [Line Items]
Revenue									1,904,695	1,809,844	1,698,525
U.S. Facilities [Member] \| Acute Inpatient Psychiatric Facilities [Member]
Disaggregation of Revenue [Line Items]
Revenue									814,124	757,211	694,151
U.S. Facilities [Member] \| Specialty Treatment Facilities [Member]
Disaggregation of Revenue [Line Items]
Revenue									761,017	725,151	702,225
U.S. Facilities [Member] \| Residential Treatment Centers [Member]
Disaggregation of Revenue [Line Items]
Revenue									293,053	284,637	256,539
U.S. Facilities [Member] \| Outpatient Community-Based Services [Member]
Disaggregation of Revenue [Line Items]
Revenue									$ 36,501	$ 42,845	$ 45,610