Summary of Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Goodwill, Beginning Balance		$ 3,784,106	$ 3,596,114
Goodwill acquired during the period		80	234,658
Adjustments to goodwill	[1]	40,971	(46,666)
Goodwill, Ending Balance		3,825,157	3,784,106
Acute Care Services
Goodwill [Line Items]
Goodwill, Beginning Balance		440,294	389,507
Goodwill acquired during the period		80	50,897
Adjustments to goodwill	[1]	1,137	(110)
Goodwill, Ending Balance		441,511	440,294
Behavioral Health Services
Goodwill [Line Items]
Goodwill, Beginning Balance		3,343,812	3,206,607
Goodwill acquired during the period		0	183,761
Adjustments to goodwill	[1]	39,834	(46,556)
Goodwill, Ending Balance		$ 3,383,646	$ 3,343,812

[1] The increase/(decrease) in the Behavioral Health Services’ goodwill consists primarily of foreign currency translation adjustments.