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Common Stock (Details 2) (USD $)
12 Months Ended
Dec. 31, 2011
Y
Dec. 31, 2010
Y
Dec. 31, 2009
Y
Assumption used in determination of fair value of share based payment awards      
Expected volatility 53.20% 55.00% 63.50%
Risk-free interest rate 2.10% 2.30% 1.80%
Expected dividends $ 0.44 $ 0.40  
Expected term (in years) 3.1 3.2 3.4