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Business Acquisitions - Additional Information (Detail) (USD $)
 6 Months Ended
Jun. 30, 2013
Company
Dec. 31, 2012
Business Acquisition [Line Items]    
Number of physician group practices acquired 5  
Business acquisition, total consideration $ 120,800,000  
Cash consideration 115,700,000  
Contingent consideration 3,800,000  
Goodwill recorded in connection with acquisitions 2,273,288,000 2,165,672,000
Current liabilities 1,300,000  
Other intangible assets 19,400,000  
Other liabilities 6,700,000  
Contingent consideration payments related to prior-period acquisitions 3,800,000  
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 4,000,000  
Time period for achievement of certain performance measures for payment of contingent consideration, years 3 years  
Goodwill deductible for tax purpose 31,800,000  
Change in goodwill carrying amount 107,600,000  
Five Physician Group Practices Acquisition [Member]
    
Business Acquisition [Line Items]    
Goodwill recorded in connection with acquisitions 108,100,000  
Prior-period Acquisition [Member]
    
Business Acquisition [Line Items]    
Contingent consideration payments related to prior-period acquisitions 7,000,000  
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 3.00%