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Fair Value of Stock-Based Awards, as Determined Under the Black-Scholes Model, Weighted-Average Assumptions (Detail)
9 Months Ended
Sep. 30, 2011
Year
Sep. 30, 2010
Year
Stock Option Awards
  
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]  
Risk-free interest rate1.00%1.55%
Expected dividend yield0.70%0.00%
Expected term4.34.3
Expected volatility42.30%45.10%
Employee Stock Purchase Plan
  
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]  
Risk-free interest rate0.10%0.30%
Expected dividend yield0.70%0.00%
Expected term66
Expected volatility21.30%23.00%