Stockholders' Equity Note Disclosure [Text Block] | 5. Stockholders’ Equity 2013 Common Stock Offering In November 2013, we sold approximately 7.7 million shares of our common stock at a public offering price of $8.00 per share. We received total net proceeds of approximately $57.8 million (net of approximately $3.9 million in issuance costs). 2014 Common Stock Offering In June 2014, we sold approximately 4.8 million shares of our common stock at a public offering price of $11.75 per share. In addition, as a component of the offering, we sold 600,000 pre-funded warrants to purchase shares of our common stock at a public offering price of $11.74 per share. The pre-funded warrants have an exercise price of $0.01 per share and expire on June 30, 2021. We received total net proceeds of approximately $58.9 million (net of approximately $4.0 million in issuance costs) from the sale of the common stock and the pre-funded warrants. 201 5 Common Stock Offering In June 2015, we sold approximately 5.5 million shares of our common stock at a public offering price of approximately $24.75 per share. We received total net proceeds of approximately $128.2 million (net of approximately $8.4 million in issuance costs) from the sale of the common stock. Private Placement Warrants In June 2011, we sold shares of common stock and warrants to purchase common stock in a private placement. A total of 4.0 million warrants to purchase common stock at an exercise price of $3.60 per share were issued as part of this private placement. The warrants were immediately exercisable and expire on July 1, 2016. The warrants may be exercised for cash only, or, if a registration statement is not then effective and available for the resale of the shares of common stock issuable upon exercise of the warrants, by surrender of such warrant, or a portion of such warrant, by way of cashless exercise. There is no right to exercise the warrants to the extent that, after giving effect to such exercise the holder would beneficially own in excess of 9.99% of our outstanding shares of common stock or such other limit as may be designated by any particular purchaser. Each holder of the warrants can amend or waive the foregoing limitation by written notice to us, with such waiver taking effect only upon the expiration of a 61-day notice period. During the nine months ended September 30, 2015, warrant holders exercised 343,813 warrants under the cashless exercise provision in each holder’s warrant, which resulted in the net issuance of 285,713 shares of common stock and no net cash proceeds to us. During the nine months ended September 30, 2014, warrant holders exercised 460,706 warrants under the cashless exercise provision in the warrant agreement, which resulted in the net issuance of 303,614 shares of common stock and no net cash proceeds to us. As of September 30, 2015, 2,965,477 warrants from the June 2011 Private Placement remain outstanding. Stock Option Exercises For the nine months ended September 30, 2015, 882,579 shares of common stock were issued pursuant to the exercise of stock options, resulting in proceeds to us of approximately $7,915,000. For the nine months ended September 30, 2014, option holders exercised 719,092 stock options, a portion of which were exercised under the cashless exercise provision of our 2007 Amended and Restated Equity Incentive Plan, resulting in the net issuance of 550,496 shares of common stock and cash proceeds to us of approximately $2,832,000. Stock-Based Compensation The following table summarizes stock-based compensation expense related to stock-based payment awards granted pursuant to all of our equity compensation arrangements for the three and nine months ended September 30, 2015 and 2014 (in thousands): Three Months Ended September 30 , Nine Months Ended September 30 , 2015 2014 2015 2014 Research and development $ 927 $ 715 $ 2,652 $ 2,423 General and administrative 1,894 1,045 5,860 3,386 Stock-based compensation expense included in operating expenses $ 2,821 $ 1,760 $ 8,512 $ 5,809 Impact on basic and diluted net loss per share $ 0.08 $ 0.06 $ 0.27 $ 0.23 As of September 30, 2015, there was $31,150,000 of total unrecognized compensation cost related to non-vested, stock-based payment awards granted under all of our equity compensation plans and all non-plan option grants. Total unrecognized compensation cost will be adjusted for future changes in estimated forfeitures. We expect to recognize this compensation cost over a weighted-average period of 2.0 years. We estimated the fair value of each option grant on the grant date using the Black-Scholes option pricing model with the following weighted-average assumptions: September 30, 20 15 20 14 Risk-free interest rate 1.7 % 2.0 % Dividend yield 0.0 % 0.0 % Volatility 90.7 % 102.9 % Expected life (years) 6 6 We estimate the fair value of each purchase right granted under the ESPP at the beginning of each new offering period using the Black-Scholes option valuation model. There were no new offering periods for the quarters ended September 30, 2015 and 2014. The following table summarizes the stock option activity for the nine months ended September 30, 2015: Weighted- Average Weighted- Remaining Average Contractual Shares Exercise Term (in thousands) Price (Years) Balance at January 1, 2015 7,918 $ 8.69 7.92 Granted 375 $ 29.26 Exercised (883 ) $ 8.97 Expired and forfeited (450 ) $ 11.02 Balance at September 30, 2015 6,960 $ 9.61 7.90 |