Stockholders' Equity	12 Months Ended
Dec. 31, 2019
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity The Company is authorized to issue 510,000,000 shares of capital stock of which 500,000,000 shares are designated as common stock and 10,000,000 shares are designated as preferred stock, all with a par value of $0.0001 per share. Each holder of common stock is entitled to one vote for each share of common stock held. The Company’s common stock is not entitled to preemptive rights, and is not subject to conversion, redemption or sinking fund provisions. Subject to preferences that may apply to any shares of preferred stock outstanding at the time, the holders of common stock are entitled to receive dividends out of funds legally available if the board of directors, in its discretion, determines to issue dividends and then only at the times and in the amounts that the board of directors may determine. As of December 31, 2019 and 2018, no common stock dividends had been declared by the board of directors and there were no shares of preferred stock outstanding. Follow-on Public Offerings In June 2017, the Company issued and sold 3,000,000 shares of common stock in an underwritten public offering pursuant to a shelf registration statement on Form S-3 at a public offering price of $4.10 per share. The net proceeds to the Company from this public offering was $11.4 million, after deducting underwriting discounts and commissions of $0.6 million and offering costs of $0.3 million. In April 2018, the Company issued and sold 5,046,510 shares of common stock in an underwritten public offering pursuant to a shelf registration statement on Form S-3 at a public offering price of $8.00 per share, including 546,510 shares of common stock issued upon the partial exercise by the underwriters of their option to purchase additional shares. The net proceeds to the Company from this public offering was $37.7 million, after deducting underwriting discounts and commissions of $2.4 million and offering costs of $0.3 million. In February 2019, the Company issued and sold 4,625,000 shares of common stock at a public offering price of $8.00 per share and pre-funded warrants to purchase up to 4,000,000 shares of common stock at a public offering price of $7.9999 per warrant in an underwritten public offering pursuant to a shelf registration statement on Form S-3. This includes the full exercise by the underwriters of their option to purchase up to 1,125,000 additional shares of common stock. The net proceeds to the Company from this offering were $64.5 million, after deducting underwriting discounts and commissions of $4.1 million and offering costs of $0.4 million. The public offering price for the pre-funded warrants was equal to the public offering price of the common stock, less the $0.0001 per share exercise price of each warrant. These warrants were recorded as a component of stockholders’ equity within additional paid-in capital and have no expiration date. Per the terms of the warrant agreement, the outstanding warrants to purchase shares of common stock may not be exercised if the holder’s ownership of the Company’s common stock would exceed 4.99% (“Maximum Ownership Percentage”). By written notice to the Company, the holders may increase or decrease the Maximum Ownership Percentage. The revised Maximum Ownership Percentage would be effective 61 days after the notice is received by the Company. As of December 31, 2019, none of the pre-funded warrants have been exercised. At-The-Market Offering In May 2017, the Company entered into a sales agreement with JonesTrading Institutional Services LLC, as sales agent and underwriter, pursuant to which the Company may issue and sell shares of its common stock for an aggregate offering price of $20.0 million under an at-the-market (“ATM’) offering program. In October 2018, the Company sold 1,845,820 shares of common stock in a single transaction pursuant to the ATM at an offering price of $9.21 per share for gross proceeds of $17.0 million, resulting in net proceeds of $16.4 million after deducting underwriting fees and offering expenses. The Company subsequently terminated the ATM sales agreement with JonesTrading in December 2018 and entered into a sales agreement with Jeffries LLC, as sales agent and underwriter, to issue and sell shares of the Company’s common stock for an aggregate offering price of $60.0 million under an ATM offering program. As of December 31, 2019, $60.0 million of the Company’s common stock remained available for sale.

Stockholders' Equity

12 Months Ended

Dec. 31, 2019

8. Stockholders’ Equity

The Company is authorized to issue 510,000,000 shares of capital stock of which 500,000,000 shares are designated as common stock and 10,000,000 shares are designated as preferred stock, all with a par value of $0.0001 per share. Each holder of common stock is entitled to one vote for each share of common stock held. The Company’s common stock is not entitled to preemptive rights, and is not subject to conversion, redemption or sinking fund provisions. Subject to preferences that may apply to any shares of preferred stock outstanding at the time, the holders of common stock are entitled to receive dividends out of funds legally available if the board of directors, in its discretion, determines to issue dividends and then only at the times and in the amounts that the board of directors may determine. As of December 31, 2019 and 2018, no common stock dividends had been declared by the board of directors and there were no shares of preferred stock outstanding.

Follow-on Public Offerings

In June 2017, the Company issued and sold 3,000,000 shares of common stock in an underwritten public offering pursuant to a shelf registration statement on Form S-3 at a public offering price of $4.10 per share. The net proceeds to the Company from this public offering was $11.4 million, after deducting underwriting discounts and commissions of $0.6 million and offering costs of $0.3 million.

In April 2018, the Company issued and sold 5,046,510 shares of common stock in an underwritten public offering pursuant to a shelf registration statement on Form S-3 at a public offering price of $8.00 per share, including 546,510 shares of common stock issued upon the partial exercise by the underwriters of their option to purchase additional shares. The net proceeds to the Company from this public offering was $37.7 million, after deducting underwriting discounts and commissions of $2.4 million and offering costs of $0.3 million.

In February 2019, the Company issued and sold 4,625,000 shares of common stock at a public offering price of $8.00 per share and pre-funded warrants to purchase up to 4,000,000 shares of common stock at a public offering price of $7.9999 per warrant in an underwritten public offering pursuant to a shelf registration statement on Form S-3. This includes the full exercise by the underwriters of their option to purchase up to 1,125,000 additional shares of common stock. The net proceeds to the Company from this offering were $64.5 million, after deducting underwriting discounts and commissions of $4.1 million and offering costs of $0.4 million.

The public offering price for the pre-funded warrants was equal to the public offering price of the common stock, less the $0.0001 per share exercise price of each warrant. These warrants were recorded as a component of stockholders’ equity within additional paid-in capital and have no expiration date. Per the terms of the warrant agreement, the outstanding warrants to purchase shares of common stock may not be exercised if the holder’s ownership of the Company’s common stock would exceed 4.99% (“Maximum Ownership Percentage”). By written notice to the Company, the holders may increase or decrease the Maximum Ownership Percentage. The revised Maximum Ownership Percentage would be effective 61 days after the notice is received by the Company. As of December 31, 2019, none of the pre-funded warrants have been exercised.

At-The-Market Offering

In May 2017, the Company entered into a sales agreement with JonesTrading Institutional Services LLC, as sales agent and underwriter, pursuant to which the Company may issue and sell shares of its common stock for an aggregate offering price of $20.0 million under an at-the-market (“ATM’) offering program. In October 2018, the Company sold 1,845,820 shares of common stock in a single transaction pursuant to the ATM at an offering price of $9.21 per share for gross proceeds of $17.0 million, resulting in net proceeds of $16.4 million after deducting underwriting fees and offering expenses.

The Company subsequently terminated the ATM sales agreement with JonesTrading in December 2018 and entered into a sales agreement with Jeffries LLC, as sales agent and underwriter, to issue and sell shares of the Company’s common stock for an aggregate offering price of $60.0 million under an ATM offering program. As of December 31, 2019, $60.0 million of the Company’s common stock remained available for sale.