Annual report pursuant to Section 13 and 15(d)

Consolidated Balance Sheets (Parenthetical)

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Consolidated Balance Sheets (Parenthetical) (USD $)
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Consolidated Balance Sheets [Abstract]      
Common stock, par value $ 0.001 $ 0.001  
Common stock, shares authorized 300,000,000 300,000,000  
Common stock, shares issued 117,593,329 117,110,703  
Common stock, shares outstanding 114,201,737 113,750,844  
Treasury stock, shares 3,391,592 3,359,859 3,305,418