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Stock-Based Compensation (Detail) - (Table 4) (USD $)
9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield 0.00% 0.00%
Weighted average fair value $ 14.05 $ 10.91
Minimum [Member]
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Volatility 41.10% 47.30%
Risk free interest rate 0.47% 0.61%
Expected life in years 3 years 1 month 2 years 9 months
Maximum [Member]
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Volatility 47.40% 48.70%
Risk free interest rate 0.87% 1.78%
Expected life in years 4 years 7 months 4 years 5 months