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Business Combinations, Intangibles and Goodwill - Additional Information (Detail) (USD $)
3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Business Acquisition [Line Items]    
Businesses acquired 2  
Business acquisition, aggregate consideration for businesses $ 102,105,000  
Cash consideration for acquisition of businesses 102,105,000 14,950,000
Consideration of acquisitions allocated to goodwill 61,700,000  
Consideration of acquisitions allocated to intangibles 33,300,000  
Consideration of acquisitions allocated to net assets $ 7,100,000