| Common stock and additional paid-in capital - $0.001 par value; 100,000,000 shares authorized; shares issued: June 30, 2011 - 31,548,668 and December 31, 2010 - 31,016,812; shares outstanding: June 30, 2011 - 28,760,459 and December 31, 2010 - 28,228,603 |