Stockholders' Equity	6 Months Ended
Jun. 30, 2019
Equity [Abstract]
Stockholders' Equity	Note 7. Stockholders’ Equity Sales Agreement On August 4, 2017, the Company entered into Amendment No. 3 to the Controlled Equity Offering ^SM Sales Agreement with Cantor Fitzgerald & Co. (as amended on August 4, 2017, the “Amended Cantor Agreement”). The Amended Cantor Agreement became effective on January 8, 2018, and provided for the issuance and sale of shares of the Company’s common stock having an aggregate offering price of up to $70.0 million through Cantor Fitzgerald & Co. (“Cantor”), which amount included the $31.4 million of unsold shares of common stock available for sale immediately prior to the effectiveness of the Amended Cantor Agreement. Under the Amended Cantor Agreement, Cantor also acts as the Company’s sales agent and receives compensation based on an aggregate of 2% of the gross proceeds on the sale price per share of its common stock. The issuance and sale of these shares by the Company pursuant to the Amended Cantor Agreement are deemed an “at-the-market” offering and are registered under the Securities Act of 1933, as amended. During the six months ended June 30, 2019, 2.0 million shares of the Company’s common stock were sold under the Amended Cantor Agreement for net proceeds of $9.8 million. At June 30, 2019, the Company had approximately $31.5 million of common stock available to be sold under the Amended Cantor Agreement.

Stockholders' Equity

6 Months Ended

Jun. 30, 2019

Note 7. Stockholders’ Equity

Sales Agreement

On August 4, 2017, the Company entered into Amendment No. 3 to the Controlled Equity Offering ^SM Sales Agreement with Cantor Fitzgerald & Co. (as amended on August 4, 2017, the “Amended Cantor Agreement”). The Amended Cantor Agreement became effective on January 8, 2018, and provided for the issuance and sale of shares of the Company’s common stock having an aggregate offering price of up to $70.0 million through Cantor Fitzgerald & Co. (“Cantor”), which amount included the $31.4 million of unsold shares of common stock available for sale immediately prior to the effectiveness of the Amended Cantor Agreement. Under the Amended Cantor Agreement, Cantor also acts as the Company’s sales agent and receives compensation based on an aggregate of 2% of the gross proceeds on the sale price per share of its common stock. The issuance and sale of these shares by the Company pursuant to the Amended Cantor Agreement are deemed an “at-the-market” offering and are registered under the Securities Act of 1933, as amended. During the six months ended June 30, 2019, 2.0 million shares of the Company’s common stock were sold under the Amended Cantor Agreement for net proceeds of $9.8 million. At June 30, 2019, the Company had approximately $31.5 million of common stock available to be sold under the Amended Cantor Agreement.