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Description of Business Basis of Presentation and Significant Accounting Policies - Additional Information (Detail) (USD $)
Share data in Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]      
Depreciation $ 41,000,000 $ 33,000,000 $ 25,000,000
Goodwill impairment charges $ 0 $ 0 $ 0
Antidilutive options to purchase were excluded from computation of diluted earnings per share 0 0 0.6
Internal-Use Software
      
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]      
Period capitalized on a straight-line basis when the asset is substantially ready for use 3    
Capitalized Software
      
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]      
Intangible assets amortizable period 4 years    
Minimum
      
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]      
Fees payment term (in days) 30    
Intangible assets amortizable period 1 year    
Maximum
      
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]      
Fees payment term (in days) 90    
Intangible assets amortizable period 10 years    
Equipment | Minimum
      
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]      
Estimated Useful Lives 3 years    
Equipment | Maximum
      
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]      
Estimated Useful Lives 20 years    
Building | Minimum
      
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]      
Estimated Useful Lives 25 years    
Building | Maximum
      
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]      
Estimated Useful Lives 45 years