Common Stock and Preferred Stock	12 Months Ended
Dec. 31, 2018
Equity [Abstract]
Common Stock and Preferred Stock	Common Stock and Preferred Stock Public Offerings In May 2015, the Company entered into a sales agreement with a sales agent to sell shares of the Company’s common stock through an “at the market” equity offering program for up to $40.0 million in total sales proceeds. Pursuant to the sales agreement, the Company sold 1,331,539 and 960,400 shares during 2016 and 2015, respectively, for net proceeds of $26.1 million and $12.5 million, respectively. The Sales Agreement automatically terminated when the Company sold the maximum number of shares allowed under the agreement. In June 2017, the Company completed an underwritten public offering of 3,450,000 shares of common stock, including the exercise by the underwriter of an over-allotment option for 450,000 shares of common stock, for total gross proceeds of $57.8 million. After underwriter’s fees and commissions and other expenses of the offering, the Company’s aggregate net proceeds were approximately $56.5 million. In January 2018, the Company entered into a Sales Agreement with a sales agent to sell shares of the Company's common stock through an “at the market” equity offering program for up to $40.0 million in gross cash proceeds. The Sales Agreement allows the Company to set the parameters for the sale of shares, including the number of shares to be issued, the time period during which sales are requested to be made, limits on the number of shares that may be sold in any one trading day and a minimum price below which sales may not be made. Under the terms of the Sales Agreement, commission expenses to the sales agent will be 3% of the gross sales price per share sold through the sales agent. The Sales Agreement shall automatically terminate upon the issuance and sale of shares that provide gross proceeds of $40.0 million and may be terminated earlier by either the Company or the sales agent upon five days’ notice. In July 2018, the Company completed an underwritten public offering of 4,600,000 shares of common stock, including the exercise in full by the underwriters of their option to purchase 600,000 additional shares of common stock in August 2018, for total gross proceeds of $57.5 million. After underwriter’s commissions and other expenses of the offering, the Company’s aggregate net proceeds were approximately $53.8 million. Common Stock Each share of common stock is entitled to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and when declared by the board of directors, subject to the prior rights of holders of other classes of stock outstanding. Preferred Stock Pursuant to the amended and restated certificate of incorporation filed by the Company immediately prior to the completion of its initial public offering, the Company’s board of directors is authorized to issue up to 15,000,000 shares of preferred stock in one or more series and to fix the rights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, redemption rights, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of such series, any or all of which may be greater than the rights of common stock. The issuance of preferred stock could adversely affect the voting power of holders of common stock and the likelihood that such holders will receive dividend payments and payments upon liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing change in the Company’s control or other corporate action. As of December 31, 2018, no shares of preferred stock were issued or outstanding, and the board of directors has not authorized or designated any rights, preferences, privileges and restrictions for any class of preferred stock. Warrants Prior to the Company’s initial public offering, warrants to purchase preferred stock were issued related to certain financing transactions. All preferred stock warrants were converted into warrants to purchase common stock upon the effectiveness of the initial public offering. In addition, the Company has issued common stock warrants to third parties in accordance with the provisions of certain debt and collaboration agreements. As of December 31, 2018, there were 905,798 common stock warrants outstanding with a weighted average exercise price of $18.38 per share and expiration dates ranging from 2022 to 2025.

Common Stock and Preferred Stock

Public Offerings

In May 2015, the Company entered into a sales agreement with a sales agent to sell shares of the Company’s common stock through an “at the market” equity offering program for up to $40.0 million in total sales proceeds. Pursuant to the sales agreement, the Company sold 1,331,539 and 960,400 shares during 2016 and 2015, respectively, for net proceeds of $26.1 million and $12.5 million, respectively. The Sales Agreement automatically terminated when the Company sold the maximum number of shares allowed under the agreement.

In June 2017, the Company completed an underwritten public offering of 3,450,000 shares of common stock, including the exercise by the underwriter of an over-allotment option for 450,000 shares of common stock, for total gross proceeds of $57.8 million. After underwriter’s fees and commissions and other expenses of the offering, the Company’s aggregate net proceeds were approximately $56.5 million.

In January 2018, the Company entered into a Sales Agreement with a sales agent to sell shares of the Company's common stock through an “at the market” equity offering program for up to $40.0 million in gross cash proceeds. The Sales Agreement allows the Company to set the parameters for the sale of shares, including the number of shares to be issued, the time period during which sales are requested to be made, limits on the number of shares that may be sold in any one trading day and a minimum price below which sales may not be made. Under the terms of the Sales Agreement, commission expenses to the sales agent will be 3% of the gross sales price per share sold through the sales agent. The Sales Agreement shall automatically terminate upon the issuance and sale of shares that provide gross proceeds of $40.0 million and may be terminated earlier by either the Company or the sales agent upon five days’ notice.

In July 2018, the Company completed an underwritten public offering of 4,600,000 shares of common stock, including the exercise in full by the underwriters of their option to purchase 600,000 additional shares of common stock in August 2018, for total gross proceeds of $57.5 million. After underwriter’s commissions and other expenses of the offering, the Company’s aggregate net proceeds were approximately $53.8 million.

Common Stock

Each share of common stock is entitled to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and when declared by the board of directors, subject to the prior rights of holders of other classes of stock outstanding.

Preferred Stock

Pursuant to the amended and restated certificate of incorporation filed by the Company immediately prior to the completion of its initial public offering, the Company’s board of directors is authorized to issue up to 15,000,000 shares of preferred stock in one or more series and to fix the rights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, redemption rights, liquidation preferences, sinking fund terms and the number of shares constituting any series or the designation of such series, any or all of which may be greater than the rights of common stock. The issuance of preferred stock could adversely affect the voting power of holders of common stock and the likelihood that such holders will receive dividend payments and payments upon liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing change in the Company’s control or other corporate action. As of December 31, 2018, no shares of preferred stock were issued or outstanding, and the board of directors has not authorized or designated any rights, preferences, privileges and restrictions for any class of preferred stock.

Warrants

Prior to the Company’s initial public offering, warrants to purchase preferred stock were issued related to certain financing transactions. All preferred stock warrants were converted into warrants to purchase common stock upon the effectiveness of the initial public offering. In addition, the Company has issued common stock warrants to third parties in accordance with the provisions of certain debt and collaboration agreements. As of December 31, 2018, there were 905,798 common stock warrants outstanding with a weighted average exercise price of $18.38 per share and expiration dates ranging from 2022 to 2025.