Schedule of Disaggregates Revenue by Major Source (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Net revenues		$ 2,648,913	$ 2,541,864	$ 8,017,782	$ 7,767,078
Percentage of Net Revenue		100.00%	100.00%	100.00%	100.00%
Medicare
Disaggregation Of Revenue [Line Items]
Net revenues		$ 451,333	$ 457,466	$ 1,416,885	$ 1,377,561
Percentage of Net Revenue		17.00%	18.00%	18.00%	18.00%
Managed Medicare
Disaggregation Of Revenue [Line Items]
Net revenues		$ 230,533	$ 202,870	$ 702,006	$ 593,436
Percentage of Net Revenue		9.00%	8.00%	9.00%	8.00%
Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues		$ 296,591	$ 298,486	$ 872,710	$ 884,498
Percentage of Net Revenue		11.00%	12.00%	11.00%	11.00%
Managed Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues		$ 365,529	$ 333,542	$ 1,130,528	$ 1,034,667
Percentage of Net Revenue		14.00%	13.00%	14.00%	13.00%
Managed Care (HMO and PPOs)
Disaggregation Of Revenue [Line Items]
Net revenues		$ 834,273	$ 806,996	$ 2,600,190	$ 2,502,998
Percentage of Net Revenue		31.00%	32.00%	32.00%	32.00%
UK Revenue
Disaggregation Of Revenue [Line Items]
Net revenues		$ 129,965	$ 110,526	$ 364,163	$ 316,938
Percentage of Net Revenue		5.00%	4.00%	5.00%	4.00%
Other Patient Revenue and Adjustments,Net
Disaggregation Of Revenue [Line Items]
Net revenues		$ 188,212	$ 162,736	$ 469,460	$ 523,642
Percentage of Net Revenue		7.00%	6.00%	6.00%	7.00%
Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues		$ 152,477	$ 169,242	$ 461,840	$ 533,338
Percentage of Net Revenue		6.00%	7.00%	6.00%	7.00%
Acute Care Hospital Services
Disaggregation Of Revenue [Line Items]
Net revenues		$ 1,383,050	$ 1,316,748	$ 4,232,673	$ 4,072,752
Percentage of Net Revenue		100.00%	100.00%	100.00%	100.00%
Acute Care Hospital Services | Medicare
Disaggregation Of Revenue [Line Items]
Net revenues		$ 295,691	$ 299,844	$ 972,073	$ 925,857
Percentage of Net Revenue		21.00%	23.00%	23.00%	23.00%
Acute Care Hospital Services | Managed Medicare
Disaggregation Of Revenue [Line Items]
Net revenues		$ 175,248	$ 160,548	$ 550,683	$ 471,727
Percentage of Net Revenue		13.00%	12.00%	13.00%	12.00%
Acute Care Hospital Services | Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues		$ 126,977	$ 121,290	$ 349,794	$ 343,675
Percentage of Net Revenue		9.00%	9.00%	8.00%	8.00%
Acute Care Hospital Services | Managed Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues		$ 123,296	$ 124,079	$ 410,243	$ 384,340
Percentage of Net Revenue		9.00%	9.00%	10.00%	9.00%
Acute Care Hospital Services | Managed Care (HMO and PPOs)
Disaggregation Of Revenue [Line Items]
Net revenues		$ 500,688	$ 471,623	$ 1,547,496	$ 1,452,448
Percentage of Net Revenue		36.00%	36.00%	37.00%	36.00%
Acute Care Hospital Services | UK Revenue
Disaggregation Of Revenue [Line Items]
Net revenues		$ 0	$ 0	$ 0	$ 0
Percentage of Net Revenue		0.00%	0.00%	0.00%	0.00%
Acute Care Hospital Services | Other Patient Revenue and Adjustments,Net
Disaggregation Of Revenue [Line Items]
Net revenues		$ 62,055	$ 26,022	$ 104,926	$ 141,919
Percentage of Net Revenue		4.00%	2.00%	2.00%	3.00%
Acute Care Hospital Services | Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues		$ 99,095	$ 113,342	$ 297,458	$ 352,786
Percentage of Net Revenue		7.00%	9.00%	7.00%	9.00%
Behavioral Health Services
Disaggregation Of Revenue [Line Items]
Net revenues	[1]	$ 1,262,472	$ 1,224,548	$ 3,774,551	$ 3,685,230
Percentage of Net Revenue		100.00%	100.00%	100.00%	100.00%
Behavioral Health Services | Medicare
Disaggregation Of Revenue [Line Items]
Net revenues		$ 155,642	$ 157,622	$ 444,812	$ 451,704
Percentage of Net Revenue		12.00%	13.00%	12.00%	12.00%
Behavioral Health Services | Managed Medicare
Disaggregation Of Revenue [Line Items]
Net revenues		$ 55,285	$ 42,322	$ 151,323	$ 121,709
Percentage of Net Revenue		4.00%	3.00%	4.00%	3.00%
Behavioral Health Services | Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues		$ 169,614	$ 177,196	$ 522,916	$ 540,823
Percentage of Net Revenue		13.00%	14.00%	14.00%	15.00%
Behavioral Health Services | Managed Medicaid
Disaggregation Of Revenue [Line Items]
Net revenues		$ 242,233	$ 209,463	$ 720,285	$ 650,327
Percentage of Net Revenue		19.00%	17.00%	19.00%	18.00%
Behavioral Health Services | Managed Care (HMO and PPOs)
Disaggregation Of Revenue [Line Items]
Net revenues		$ 333,585	$ 335,373	$ 1,052,694	$ 1,050,550
Percentage of Net Revenue		26.00%	27.00%	28.00%	29.00%
Behavioral Health Services | UK Revenue
Disaggregation Of Revenue [Line Items]
Net revenues		$ 129,965	$ 110,526	$ 364,163	$ 316,938
Percentage of Net Revenue		10.00%	9.00%	10.00%	9.00%
Behavioral Health Services | Other Patient Revenue and Adjustments,Net
Disaggregation Of Revenue [Line Items]
Net revenues		$ 126,157	$ 136,714	$ 364,534	$ 381,723
Percentage of Net Revenue		10.00%	11.00%	10.00%	10.00%
Behavioral Health Services | Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues		$ 49,991	$ 55,332	$ 153,824	$ 171,456
Percentage of Net Revenue		4.00%	5.00%	4.00%	5.00%
Other
Disaggregation Of Revenue [Line Items]
Net revenues		$ 3,391	$ 568	$ 10,558	$ 9,096
Other | Other Non-patient Revenue
Disaggregation Of Revenue [Line Items]
Net revenues		$ 3,391	$ 568	$ 10,558	$ 9,096

[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.