Stockholders' Equity	6 Months Ended
Jun. 30, 2020
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity In June 2020, the Company issued and sold in an underwritten public offering an aggregate of 10,162,059 shares of common stock, including an additional 1,071,149 shares of common stock upon the partial exercise of an option of the underwriter to purchase additional shares, for a purchase price to the public of $1.10 per share. The Company received aggregate gross proceeds from the public offering of approximately $11,178, before deducting underwriting discounts and commissions and offering expenses of $932. In July 2019, the Company entered into the Sales Agreement with JonesTrading, under which the Company may issue and sell shares of common stock, from time to time, having an aggregate offering price of up to $13,265. Sales of common stock through JonesTrading may be made by any method that is deemed an “at the market” offering as defined in Rule 415(a)(4) under the Securities Act of 1933, as amended. The Company is not obligated to make any sales of its common stock under the Sales Agreement. The Company began selling shares of common stock under the Sales Agreement in April 2020. During the six months ended June 30, 2020 the Company issued and sold an aggregate of 1,263,059 shares of common stock for gross proceeds of $762, before deducting commissions and fees of $24. In June 2020, the Company terminated offer and sale of shares of common stock under the Sales Agreement with JonesTrading. On April 2, 2019, the Company issued and sold in a private placement an aggregate of (i) 11,838,582 units, consisting of 11,838,582 shares of its common stock and associated warrants, (the “common warrants”), to purchase an aggregate of 11,838,582 shares of common stock, for a combined price of $2.01 per unit and (ii) 1,096,741 units, consisting of (a) pre-funded warrants to purchase 1,096,741 shares of the Company’s common stock and (b) associated common warrants to purchase 1,096,741 shares of common stock, for a combined price of $2.01 per unit. The pre-funded warrants had an exercise price of $0.01 per share and had no expiration. The common warrants are exercisable at an exercise price of $2.00 per share and expire five years from the date of issuance. The securities were sold pursuant to a securities purchase agreement entered into with accredited investors on March 28, 2019. The Company received aggregate gross proceeds from the private placement of approximately $26,000 before deducting placement agent fees and offering expenses of $2,175 and excluding the exercise of any warrants. The Company evaluated the terms of the common warrants issued and determined that they should be classified as equity instruments. The grant date fair value of the common warrants was estimated to be $1.78 per share, for a total of approximately $23,025. The Company estimated the fair value of the common warrants using a Black-Scholes model utilizing the following key valuation assumptions: the Company’s stock price, a risk free rate of 2.23%, an expected life of five years and an expected volatility of 76%. The Company evaluated the terms of the pre-funded warrants and classified them as equity. The pre-funded warrants were exercised in full in July 2019.

Stockholders' Equity

6 Months Ended

Jun. 30, 2020

8. Stockholders’ Equity

In June 2020, the Company issued and sold in an underwritten public offering an aggregate of 10,162,059 shares of common stock, including an additional 1,071,149 shares of common stock upon the partial exercise of an option of the underwriter to purchase additional shares, for a purchase price to the public of $1.10 per share. The Company received aggregate gross proceeds from the public offering of approximately $11,178, before deducting underwriting discounts and commissions and offering expenses of $932.

In July 2019, the Company entered into the Sales Agreement with JonesTrading, under which the Company may issue and sell shares of common stock, from time to time, having an aggregate offering price of up to $13,265. Sales of common stock through JonesTrading may be made by any method that is deemed an “at the market” offering as defined in Rule 415(a)(4) under the Securities Act of 1933, as amended. The Company is not obligated to make any sales of its common stock under the Sales Agreement. The Company began selling shares of common stock under the Sales Agreement in April 2020. During the six months ended June 30, 2020 the Company issued and sold an aggregate of 1,263,059 shares of common stock for gross proceeds of $762, before deducting commissions and fees of $24. In June 2020, the Company terminated offer and sale of shares of common stock under the Sales Agreement with JonesTrading.

On April 2, 2019, the Company issued and sold in a private placement an aggregate of (i) 11,838,582 units, consisting of 11,838,582 shares of its common stock and associated warrants, (the “common warrants”), to purchase an aggregate of 11,838,582 shares of common stock, for a combined price of $2.01 per unit and (ii) 1,096,741 units, consisting of (a) pre-funded warrants to purchase 1,096,741 shares of the Company’s common stock and (b) associated common warrants to purchase 1,096,741 shares of common stock, for a combined price of $2.01 per unit. The pre-funded warrants had an exercise price of $0.01 per share and had no expiration. The common warrants are exercisable at an exercise price of $2.00 per share and expire five years from the date of issuance. The securities were sold pursuant to a securities purchase agreement entered into with accredited investors on March 28, 2019. The Company received aggregate gross proceeds from the private placement of approximately $26,000 before deducting placement agent fees and offering expenses of $2,175 and excluding the exercise of any warrants.

The Company evaluated the terms of the common warrants issued and determined that they should be classified as equity instruments. The grant date fair value of the common warrants was estimated to be $1.78 per share, for a total of approximately $23,025. The Company estimated the fair value of the common warrants using a Black-Scholes model utilizing the following key valuation assumptions: the Company’s stock price, a risk free rate of 2.23%, an expected life of five years and an expected volatility of 76%. The Company evaluated the terms of the pre-funded warrants and classified them as equity.

The pre-funded warrants were exercised in full in July 2019.