Business Acquisitions, Joint Ventures and Goodwill - Additional Information (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) Company	Dec. 31, 2017 USD ($)
Business Acquisition [Line Items]
Number of physician group practices acquired | Company	5
Number of neonatology practices acquired | Company	1
Number of other pediatric subspecialty practices acquired | Company	2
Number of radiology practices acquired | Company	2
Total business acquisition consideration	$ 24,400
Goodwill	4,303,427	$ 4,283,963
Contingent consideration payments related to prior-period acquisitions	4,600
Purchase consideration payments related to prior-period acquisitions	1,200
Change in the fair value of a contingent consideration	(2,500)
Assets held for sale	$ 46,000
Sale of equity method investments	49.00%
Management Services Reporting Unit [Member]
Business Acquisition [Line Items]
Goodwill	$ 321,600
Physician Group [Member]
Business Acquisition [Line Items]
Goodwill	15,500
Other intangible assets	8,900
Prior-Period Acquisitions [Member]
Business Acquisition [Line Items]
Decrease in current assets	1,200
Decrease in noncurrent assets	1,500
Decrease in noncurrent liabilities	200
Net increase in goodwill resulting from finalization of tax acquisition accounting	4,000
Goodwill deductible for tax purposes	18,200
Additional cash consideration related to a working capital true up	$ 1,500