Segment Reporting (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Gross inpatient revenues		$ 8,468,381	$ 7,601,856	$ 25,845,309	$ 23,062,840
Gross outpatient revenues		3,936,556	3,435,625	11,934,261	10,520,504
Total net revenues		2,648,913	2,541,864	8,017,782	7,767,078
Income/(loss) before allocation of corporate overhead and income taxes		229,067	220,354	827,075	833,051
Allocation of corporate overhead		0	0	0	0
Income/(loss) after allocation of corporate overhead and before income taxes		229,067	220,354	827,075	833,051
Total assets		11,273,585	10,639,360	11,273,585	10,639,360	$ 10,761,828
Acute Care Hospital Services
Segment Reporting Information [Line Items]
Gross inpatient revenues		6,009,303	5,344,625	18,535,079	16,373,472
Gross outpatient revenues		3,694,389	3,199,066	11,169,376	9,780,173
Total net revenues		1,383,050	1,316,748	4,232,673	4,072,752
Income/(loss) before allocation of corporate overhead and income taxes		147,448	106,707	513,174	452,388
Allocation of corporate overhead		(49,967)	(45,680)	(149,760)	(137,031)
Income/(loss) after allocation of corporate overhead and before income taxes		97,481	61,027	363,414	315,357
Total assets		4,027,573	3,736,676	4,027,573	3,736,676
Behavioral Health Services
Segment Reporting Information [Line Items]
Gross inpatient revenues	[1]	2,459,078	2,257,231	7,310,230	6,689,368
Gross outpatient revenues	[1]	242,167	236,559	764,885	740,331
Total net revenues	[1]	1,262,472	1,224,548	3,774,551	3,685,230
Income/(loss) before allocation of corporate overhead and income taxes	[1]	234,170	228,673	734,362	732,749
Allocation of corporate overhead	[1]	(40,244)	(39,707)	(120,822)	(119,021)
Income/(loss) after allocation of corporate overhead and before income taxes	[1]	193,926	188,966	613,540	613,728
Total assets	[1]	6,871,765	6,610,811	6,871,765	6,610,811
Other
Segment Reporting Information [Line Items]
Gross inpatient revenues		0	0	0	0
Gross outpatient revenues		0	0	0	0
Total net revenues		3,391	568	10,558	9,096
Income/(loss) before allocation of corporate overhead and income taxes		(152,551)	(115,026)	(420,461)	(352,086)
Allocation of corporate overhead		90,211	85,387	270,582	256,052
Income/(loss) after allocation of corporate overhead and before income taxes		(62,340)	(29,639)	(149,879)	(96,034)
Total assets		$ 374,247	$ 291,873	$ 374,247	$ 291,873

[1] Includes net revenues generated from our behavioral health care facilities located in the U.K. amounting to approximately $130 million and $111 million for the three-month periods ended September 30, 2018 and 2017, respectively, and approximately $364 million and $317 million for the nine-month periods ended September 30, 2018 and 2017 respectively. Total assets at our U.K. behavioral health care facilities were approximately $1.231 billion and $1.094 billion as of September 30, 2018 and 2017, respectively.