Quarterly report pursuant to Section 13 or 15(d)

Consolidated Balance Sheets (Parenthetical)

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Consolidated Balance Sheets (Parenthetical) (USD $)
Sep. 30, 2013
Dec. 31, 2012
Stockholders' equity    
Common stock, par value (in dollars per share) $ 0.001 $ 0.001
Common stock, shares authorized (in shares) 100,000,000 100,000,000
Common stock, shares issued (in shares) 57,872,798 55,339,160
Common stock, shares outstanding (in shares) 54,767,551 52,329,248
Treasury stock, at cost (in shares) 3,105,247 3,009,912