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Business Acquisitions - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2012
Company
Mar. 31, 2013
Prior-Periods Acquisition [Member]
Business Acquisition [Line Items]    
Contingent consideration payments related to prior-period acquisitions   $ 1.7
Prior-period acquisition of other assets   0.5
Number of physician group practices acquired 4  
Business acquisition, total consideration 32.9  
Cash consideration 26.8  
Contingent consideration 6.1  
Goodwill recorded in connection with acquisitions 24.6  
Other intangible assets $ 8.3