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Employee Stock-Based Compensation (Tables)
9 Months Ended
Sep. 30, 2011
Employee Stock Based Compensation (Tables) [Abstract] 
Weighted average assumptions in valuation model
 
         
Expected holding period (in years)
    5.2  
Expected volatility
    26.4 %
Expected dividend yield
    2.8 %
Risk-free interest rate
    2.2 %