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Business Acquisitions - Additional Information (Detail)
$ in Millions
 3 Months Ended 9 Months Ended
Mar. 31, 2017
USD ($)
shares
Sep. 30, 2017
USD ($)
Company
shares
Business Acquisition [Line Items]    
Number of physician group practices acquired | Company   9
Number of neonatology practices acquired | Company   1
Number of maternal-fetal medicine practices acquired | Company   2
Number of other pediatric subspecialty practices acquired | Company   2
Number of pediatric multi-specialty practice acquired | Company   1
Number of radiology practices acquired | Company   3
Total business acquisition consideration   $ 356.6
Cash payments to acquire businesses   355.1
Fair value of equity interest $ 0.5 $ 0.5
Number of shares issued for business acquisition | shares 8,804 8,804
Purchase consideration liability   $ 1.0
Contractual restriction period on disposition or assignment of common stock 3 years  
Goodwill deductible for tax purposes   170.8
Contingent consideration payments related to prior-period acquisitions   4.4
Assets held for sale   46.0
Sale of minority interest percentage 75.00%  
Deconsolidation percentage 100.00%  
Prior-Period Acquisitions [Member]    
Business Acquisition [Line Items]    
Increase in deferred tax liabilities   0.5
Increase in goodwill resulting from finalization of tax acquisition accounting   $ 0.5