7. Stockholders' Equity

Equity Offerings

        On September 16, 2015, the Company issued and sold 7,475,000 shares of common stock in a public offering at a price of $9.75 per share, for gross proceeds of approximately $72.9 million. The net offering proceeds to the Company were approximately $68.3 million, after deducting underwriting discounts and commissions of approximately $4.4 million and offering costs of $0.2 million.

        On July 7, 2015, the Company issued and sold 1,000,000 shares of common stock through Cowen and Company, LLC (Cowen), pursuant to an at-the-market (ATM) sales facility dated April 3, 2015. The shares were sold at a weighted average price per share of $6.0001, for aggregate gross proceeds of $6.0 million. The net offering proceeds to the Company were approximately $5.8 million after deducting related expenses, including commissions of approximately $0.2 million.

        On May 8, 2015, the Company issued and sold 2,700,000 shares of common stock through Cowen pursuant to the ATM facility at a weighted average price per share of $6.2503, for aggregate gross proceeds of $16.9 million. The net offering proceeds to the Company were approximately $16.2 million after deducting related expenses, including commissions of approximately $0.5 million.

        On December 10, 2014, the Company issued and sold 11,250,000 shares of common stock in a public offering of shares as well as 1,598,000 shares of common stock pursuant to the partial exercise of the underwriters' over-allotment option for a total of 12,848,000 shares at a price of $4.00 per share, for aggregate gross proceeds of approximately $51.4 million.

        On February 5, 2014, the Company issued and sold 9,250,000 shares of common stock in an IPO at a price of $7.00 per share, for aggregate gross proceeds of approximately $64.8 million. On March 6, 2014, in connection with the partial exercise of the IPO underwriters' over-allotment option, the Company sold an additional 270,449 shares of common stock at a price of $7.00 per share, for aggregate gross proceeds of approximately $1.9 million.

        Under its certificate of incorporation, the Company was authorized to issue up to 100,000,000 shares of common stock as of December 31, 2015 and December 31, 2014, respectively. The Company also was authorized to issue up to 5,000,000 shares of preferred stock as of December 31, 2015. The Company is required, at all times, to reserve and keep available out of its authorized but unissued shares of common stock sufficient shares to effect the conversion of the shares of the preferred stock and all outstanding stock options and warrants.

Equity Incentive Plans

        In 2008, the Company adopted the 2008 Equity Incentive Plan, as amended on February 29, 2008, January 7, 2010, July 8, 2010, December 10, 2010, June 23, 2011 and June 17, 2013 (collectively, the "2008 Plan") that authorized the Company to grant restricted stock and stock options to eligible employees, directors and consultants to the Company.

        In 2013, the Company adopted the 2013 Equity Incentive Plan, as amended on May 14, 2014 (collectively, the "2013 Plan"). The 2013 Plan became effective upon the Company's entry into the underwriting agreement related to its initial public offering (IPO) in January 2014 and, as of such date, the Company may not make further grants under the 2008 Plan. The 2013 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance-based stock awards and other forms of equity compensation (collectively, stock awards), all of which may be granted to employees, including officers, non-employee directors and consultants of the Company. Additionally, the 2013 Plan provides for the grant of cash and stock based performance awards. The 2013 Plan contains an "evergreen" provision, pursuant to which the number of shares of common stock available for issuance under the plan automatically increases on January 1 of each year beginning in 2015.

        Under both the 2008 and 2013 Plans, the amount, terms of grants and exercisability provisions are determined by the board of directors or its designee. The term of the options may be up to 10 years, and options are exercisable in cash or as otherwise determined by the board of directors. Vesting generally occurs over a period of not greater than four years.

        The estimated grant-date fair value of the Company's share-based awards is amortized ratably over the awards' service periods. Share-based compensation expense recognized was as follows:

                                                                                                                                                                                    

 

                                                                                                                                                                                    

        The intrinsic value of the options exercisable as of December 31, 2015 was $14.4 million, based on the Company's closing stock price of $10.50 per share and a weighted average exercise price of $3.10 per share.

        The Company uses the Black-Scholes option-pricing model to estimate the fair value of stock options at the grant date. The Black-Scholes model requires the Company to make certain estimates and assumptions, including estimating the fair value of the Company's common stock, assumptions related to the expected price volatility of the Company's stock, the period during which the options will be outstanding, the rate of return on risk-free investments and the expected dividend yield for the Company's stock.

        The per-share weighted-average grant date fair value of the options granted to employees and directors during the year ended December 31, 2015 and 2014 was estimated at $4.49 and $4.43 per share, respectively, on the date of grant using the Black-Scholes option-pricing model with the following weighted-average assumptions:

                                                                                                                                                                                    

        The weighted-average valuation assumptions were determined as follows:

        The fair value of the Company's common stock, prior to the IPO, was determined by its board of directors with assistance from its management. The board of directors and management considered numerous objective and subjective factors in the assessment of fair value, including the price for the Company's preferred stock that was sold to investors and the rights, preferences and privileges of the preferred stock and common stock, the Company's financial condition and results of operations during the relevant periods and the status of strategic initiatives. These estimates involved a significant level of judgment.

        As of December 31, 2015, there was $9.0 million of total unrecognized compensation expense related to unvested options that will be recognized over the weighted average remaining period of 2.76 years.

Shares Available for Future Grant

        At December 31, 2015, the Company has the following shares available to be granted under the 2013 Plan:

                                                                                                                                                                                    

Shares Reserved for Future Issuance

        At December 31, 2015, the Company has reserved the following shares of common stock for issuance: