Common Stock	3 Months Ended
Mar. 31, 2021
Equity [Abstract]
Common Stock	(7) Common Stock As of March 31, 2021, the Company had 50,000,000 authorized shares of common stock, $0.001 par value, of which 34,360,775 shares were issued and outstanding. Public Offering – March 2021 On March 26, 2021, the Company completed an underwritten public offering of 6,900,000 shares of its common stock, including the full exercise by the underwriters of their option to purchase an additional 900,000 shares, at the public offering price of $8.00 per share for gross proceeds of approximately $55.2 million. The net offering proceeds to the Company were approximately $51.6 million after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company. Universal Shelf Registration Statement On November 9, 2020, the Company filed a shelf registration statement on Form S-3 with the SEC, which covers the offering, issuance and sale of up to $300.0 million of its common stock, preferred stock, debt securities, warrants and/or units (the “2020 Shelf”). The 2020 Shelf (File No. 333-249982) was declared effective by the SEC on November 18, 2020 and was filed to replace the Company’s then existing shelf registration statement, which was terminated. As of March 31, 2021, there was approximately $213.0 million available for future issuance of common stock, preferred stock, debt securities, warrants and/or units. Public Offering – June 2020 On June 19, 2020, the Company completed an underwritten public offering of 9,725,000 shares of its common stock, including the partial exercise by the underwriters of their option to purchase an additional 1,225,000 shares, at the public offering price of $5.25 per share for gross proceeds of approximately $51.1 million. Three stockholders beneficially holding more than 5% of the Company’s voting securities, including an entity affiliated with New Enterprise Associates and two other stockholders, purchased an aggregate of 4,503,571 shares in this offering at the same public offering price per share as the other investors. At such time, entities affiliated with New Enterprise Associates (collectively) beneficially held more than 5% of the Company’s voting securities. The net offering proceeds to the Company were approximately $47.7 million after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company. Public Offering – April 2019 (Offering Warrant Expiration – April 8,2021) In April 2019, the Company completed an underwritten public offering of 2,173,913 shares of its common stock and warrants to purchase an aggregate of 2,500,000 shares of its common stock (“the Offering Warrants”), including warrants to purchase an aggregate of 326,086 shares of its common stock sold pursuant to the underwriter’s partial exercise of its overallotment option, at the public offering price of $11.40 per share and $0.10 per warrant for gross proceeds of approximately $25.0 million. The Offering Warrants were immediately exercisable upon issuance at an exercise price of $12.50 per share, subject to adjustment in certain circumstances, and expired two years from the date of issuance on April 8, 2021. Any Offering Warrants that had not been exercised for cash prior to their expiration were to be automatically exercised via cashless exercise on the expiration date. The shares and warrants were issued separately and were separately transferable. An entity affiliated with New Enterprise Associates purchased 434,782 shares and warrants to purchase an aggregate of 434,782 shares in this offering at the same public offering price per share as the other investors. At such time, entities affiliated with New Enterprise Associates (collectively) beneficially held more than 5% of the Company’s voting securities. The net offering proceeds to the Company were approximately $22.8 million after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company. The Company determined the shares of common stock and the Offering Warrants represented freestanding financial instruments. In addition, the Company conducted an assessment of the classification of the Offering Warrants and, based on their terms, concluded the Offering Warrants were equity-classified. Accordingly, the net offering proceeds of $22.8 million were recorded within stockholders’ equity (deficit). In March 2021, Offering Warrants exercisable for 247,391 shares of common stock had been exercised, for approximately $3.1 million in cash proceeds, and Offering Warrants exercisable for 2,252,609 shares of common stock were outstanding as of March 31, 2021. On April 8, 2021, all of the remaining 2,252,609 Offering Warrants expired and no shares of the Company’s common stock were issued via automatic cashless exercises of unexercised warrants on the date of expiration as the $12.50 exercise price was greater than the Company’s closing stock price of $7.01 on April 8, 2021. Sales Agreement with SVB Leerink In February 2018, the Company entered into a sales agreement with SVB Leerink LLC (“SVB Leerink” and the “SVB Leerink Sales Agreement”) pursuant to which the Company may issue and sell shares of its common stock from time to time up to an aggregate amount of $50.0 million, at its option, through SVB Leerink as its sales agent, with any sales of common stock through SVB Leerink being made by any method that is deemed an “at-the-market offering” as defined in Rule 415 promulgated under the Securities Act of 1933, as amended (the “Securities Act”), or in other transactions pursuant to an effective shelf registration statement on Form S-3. The Company agreed to pay SVB Leerink a commission of up to 3% of the gross proceeds of any sales of common stock pursuant to the SVB Leerink Sales Agreement. The Company sold 470,777 shares, 1,251,555 shares, 1,070,175 shares and 330,688 shares pursuant to the SVB Leerink Sales Agreement, resulting in proceeds net of commissions of approximately $10.3 million, $7.5 million, $5.9 million and $3.4 million in the fourth quarter of 2018, February 2019, November 2020 and March 2021, respectively. As of March 31, 2021, approximately $22.2 million was available for issuance in connection with future stock sales pursuant to the SVB Leerink Sales Agreement. Private Placement – May 2016 (PIPE Warrant Expiration - Scheduled on May 16, 2021) In May 2016, the Company entered into a securities purchase agreement with a select group of qualified institutional buyers, institutional accredited investors and accredited investors pursuant to which the Company sold 1,764,242 units, at a price of $9.65 per unit, for gross proceeds of approximately $17.0 million. Each unit consisted of one share of the Company’s common stock and a warrant to purchase one share of the Company’s common stock (the “PIPE Warrants”). The PIPE Warrants have an exercise price of $10.00 per share and are exercisable for a period of five years from the date of issuance until their scheduled expiration on May 16, 2021. Certain of the Company’s directors and executive officers purchased an aggregate of 54,402 units in this offering at the same price as the other investors. The net offering proceeds to the Company were approximately $15.4 million after deducting placement agent fees and other offering expenses payable by the Company. As of March 31, 2021, PIPE Warrants exercisable for 80,309 shares of common stock had been exercised, for approximately $0.8 million in cash proceeds, and PIPE Warrants exercisable for 1,683,933 shares of common stock were outstanding.

Common Stock

3 Months Ended

Mar. 31, 2021

(7) Common Stock

As of March 31, 2021, the Company had 50,000,000 authorized shares of common stock, $0.001 par value, of which 34,360,775 shares were issued and outstanding.

Public Offering – March 2021

On March 26, 2021, the Company completed an underwritten public offering of 6,900,000 shares of its common stock, including the full exercise by the underwriters of their option to purchase an additional 900,000 shares, at the public offering price of $8.00 per share for gross proceeds of approximately $55.2 million. The net offering proceeds to the Company were approximately $51.6 million after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company.

Universal Shelf Registration Statement

On November 9, 2020, the Company filed a shelf registration statement on Form S-3 with the SEC, which covers the offering, issuance and sale of up to $300.0 million of its common stock, preferred stock, debt securities, warrants and/or units (the “2020

Shelf”). The 2020 Shelf (File No. 333-249982) was declared effective by the SEC on November 18, 2020 and was filed to replace the Company’s then existing shelf registration statement, which was terminated. As of March 31, 2021, there was approximately $213.0 million available for future issuance of common stock, preferred stock, debt securities, warrants and/or units.

Public Offering – June 2020

On June 19, 2020, the Company completed an underwritten public offering of 9,725,000 shares of its common stock, including the partial exercise by the underwriters of their option to purchase an additional 1,225,000 shares, at the public offering price of $5.25 per share for gross proceeds of approximately $51.1 million. Three stockholders beneficially holding more than 5% of the Company’s voting securities, including an entity affiliated with New Enterprise Associates and two other stockholders, purchased an aggregate of 4,503,571 shares in this offering at the same public offering price per share as the other investors. At such time, entities affiliated with New Enterprise Associates (collectively) beneficially held more than 5% of the Company’s voting securities. The net offering proceeds to the Company were approximately $47.7 million after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company.

Public Offering – April 2019 (Offering Warrant Expiration – April 8,2021)

In April 2019, the Company completed an underwritten public offering of 2,173,913 shares of its common stock and warrants to purchase an aggregate of 2,500,000 shares of its common stock (“the Offering Warrants”), including warrants to purchase an aggregate of 326,086 shares of its common stock sold pursuant to the underwriter’s partial exercise of its overallotment option, at the public offering price of $11.40 per share and $0.10 per warrant for gross proceeds of approximately $25.0 million. The Offering Warrants were immediately exercisable upon issuance at an exercise price of $12.50 per share, subject to adjustment in certain circumstances, and expired two years from the date of issuance on April 8, 2021. Any Offering Warrants that had not been exercised for cash prior to their expiration were to be automatically exercised via cashless exercise on the expiration date. The shares and warrants were issued separately and were separately transferable. An entity affiliated with New Enterprise Associates purchased 434,782 shares and warrants to purchase an aggregate of 434,782 shares in this offering at the same public offering price per share as the other investors. At such time, entities affiliated with New Enterprise Associates (collectively) beneficially held more than 5% of the Company’s voting securities. The net offering proceeds to the Company were approximately $22.8 million after deducting underwriting discounts and commissions and estimated offering expenses payable by the Company. The Company determined the shares of common stock and the Offering Warrants represented freestanding financial instruments. In addition, the Company conducted an assessment of the classification of the Offering Warrants and, based on their terms, concluded the Offering Warrants were equity-classified. Accordingly, the net offering proceeds of $22.8 million were recorded within stockholders’ equity (deficit).

In March 2021, Offering Warrants exercisable for 247,391 shares of common stock had been exercised, for approximately $3.1 million in cash proceeds, and Offering Warrants exercisable for 2,252,609 shares of common stock were outstanding as of March 31, 2021. On April 8, 2021, all of the remaining 2,252,609 Offering Warrants expired and no shares of the Company’s common stock were issued via automatic cashless exercises of unexercised warrants on the date of expiration as the $12.50 exercise price was greater than the Company’s closing stock price of $7.01 on April 8, 2021.

Sales Agreement with SVB Leerink

In February 2018, the Company entered into a sales agreement with SVB Leerink LLC (“SVB Leerink” and the “SVB Leerink Sales Agreement”) pursuant to which the Company may issue and sell shares of its common stock from time to time up to an aggregate amount of $50.0 million, at its option, through SVB Leerink as its sales agent, with any sales of common stock through SVB Leerink being made by any method that is deemed an “at-the-market offering” as defined in Rule 415 promulgated under the Securities Act of 1933, as amended (the “Securities Act”), or in other transactions pursuant to an effective shelf registration statement on Form S-3. The Company agreed to pay SVB Leerink a commission of up to 3% of the gross proceeds of any sales of common stock pursuant to the SVB Leerink Sales Agreement. The Company sold 470,777 shares, 1,251,555 shares, 1,070,175 shares and 330,688 shares pursuant to the SVB Leerink Sales Agreement, resulting in proceeds net of commissions of approximately $10.3 million, $7.5 million, $5.9 million and $3.4 million in the fourth quarter of 2018, February 2019, November 2020 and March 2021, respectively. As of March 31, 2021, approximately $22.2 million was available for issuance in connection with future stock sales pursuant to the SVB Leerink Sales Agreement.

Private Placement – May 2016 (PIPE Warrant Expiration - Scheduled on May 16, 2021)

In May 2016, the Company entered into a securities purchase agreement with a select group of qualified institutional buyers, institutional accredited investors and accredited investors pursuant to which the Company sold 1,764,242 units, at a price of $9.65 per unit, for gross proceeds of approximately $17.0 million. Each unit consisted of one share of the Company’s common stock and a warrant to purchase one share of the Company’s common stock (the “PIPE Warrants”). The PIPE Warrants have an exercise price of

$10.00 per share and are exercisable for a period of five years from the date of issuance until their scheduled expiration on May 16, 2021. Certain of the Company’s directors and executive officers purchased an aggregate of 54,402 units in this offering at the same price as the other investors. The net offering proceeds to the Company were approximately $15.4 million after deducting placement agent fees and other offering expenses payable by the Company. As of March 31, 2021, PIPE Warrants exercisable for 80,309 shares of common stock had been exercised, for approximately $0.8 million in cash proceeds, and PIPE Warrants exercisable for 1,683,933 shares of common stock were outstanding.