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Stock-based Compensation - Schedule of Estimated Per Share Weighted Average Fair Value and Assumptions Used to Estimate Fair Value (Detail) (ESPP [Member], USD $)
6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Employee Stock Purchase Plan [Line Items]    
Weighted average fair value per share $ 6.68 $ 5.64
Minimum [Member]
   
Employee Stock Purchase Plan [Line Items]    
Expected volatility 29.00% 38.00%
Risk-free interest rate 0.10% 0.10%
Expected term (in years) 6 months 6 months
Maximum [Member]
   
Employee Stock Purchase Plan [Line Items]    
Expected volatility 38.00% 49.00%
Risk-free interest rate 0.30% 0.20%
Expected term (in years) 2 years 2 years