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Business Acquisitions - Additional Information (Detail) (USD $)
 9 Months Ended
Sep. 30, 2013
Company
Dec. 31, 2012
Business Acquisition [Line Items]    
Number of physician group practices acquired 8  
Business acquisition, total consideration $ 205,600,000  
Cash consideration 192,200,000  
Contingent consideration 13,400,000  
Goodwill recorded in connection with acquisitions 2,354,189,000 2,165,672,000
Other intangible assets 24,900,000  
Other liabilities 8,300,000  
Contingent consideration payments related to prior-period acquisitions 13,400,000  
Assumed payment probability of contingent consideration payment 100.00%  
Range of the undiscounted amount under contingent consideration agreement, low 0  
Range of the undiscounted amount under contingent consideration agreement, high 14,600,000  
Time period for achievement of certain performance measures for payment of contingent consideration, years 5 years  
Goodwill deductible for tax purpose 58,000,000  
Change in goodwill carrying amount 188,500,000  
Eight Physician Group Practices Acquisition [Member]
    
Business Acquisition [Line Items]    
Goodwill recorded in connection with acquisitions 189,000,000  
Prior-Period Acquisition [Member]
    
Business Acquisition [Line Items]    
Contingent consideration payments related to prior-period acquisitions 7,600,000  
Prior-period acquisition of other assets $ 500,000  
Minimum [Member]
    
Business Acquisition [Line Items]    
Assumed discount rates for acquisition-date fair value 2.50%  
Maximum [Member]
    
Business Acquisition [Line Items]    
Assumed discount rates for acquisition-date fair value 4.00%