Stockholders' Equity	6 Months Ended
Jun. 30, 2018
Equity [Abstract]
Stockholders' Equity	Note 7. Stockholders’ Equity Public Offering of Common Stock In January 2018, the Company issued and sold 14,030,000 shares of the Company’s common stock, par value $0.001 per share, at $4.10 per share in an underwritten public offering. The proceeds to the Company from this offering were approximately $57.2 million, net of the underwriting discount and other issuance costs. Sales Agreement On May 5, 2016, the Company entered into Amendment No. 2 to the Controlled Equity Offering^SM Sales Agreement (as amended on May 5, 2016, the “Prior Cantor Agreement”) with Cantor Fitzgerald & Co. (“Cantor”) that provided for the issuance and sale of shares of the Company’s common stock having an aggregate offering price of up to $132.2 million through Cantor. As a result of Amendment No. 2, at May 5, 2016, the Company had $70 million of common stock available to be sold under the Prior Cantor Agreement. On August 4, 2017, the Company entered into Amendment No. 3 to the Cantor Agreement (as amended on August 4, 2017, the “Amended Cantor Agreement”). The Amended Cantor Agreement became effective on January 8, 2018, and provides 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, which amount included the $31.4 million of unsold shares of common stock available for sale under the Prior Cantor Agreement 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 registered under the Securities Act of 1933, as amended. During the six months ended June 30, 2018, 1.8 million shares of the Company’s common stock were sold under the Amended Cantor Agreement for net proceeds of $11.9 million. At June 30, 2018, the Company had approximately $57.8 million of common stock available to be sold under the Amended Cantor Agreement.

Note 7. Stockholders’ Equity

Public Offering of Common Stock

In January 2018, the Company issued and sold 14,030,000 shares of the Company’s common stock, par value $0.001 per share, at $4.10 per share in an underwritten public offering. The proceeds to the Company from this offering were approximately $57.2 million, net of the underwriting discount and other issuance costs.

Sales Agreement

On May 5, 2016, the Company entered into Amendment No. 2 to the Controlled Equity Offering^SM Sales Agreement (as amended on May 5, 2016, the “Prior Cantor Agreement”) with Cantor Fitzgerald & Co. (“Cantor”) that provided for the issuance and sale of shares of the Company’s common stock having an aggregate offering price of up to $132.2 million through Cantor. As a result of Amendment No. 2, at May 5, 2016, the Company had $70 million of common stock available to be sold under the Prior Cantor Agreement.

On August 4, 2017, the Company entered into Amendment No. 3 to the Cantor Agreement (as amended on August 4, 2017, the “Amended Cantor Agreement”). The Amended Cantor Agreement became effective on January 8, 2018, and provides 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, which amount included the $31.4 million of unsold shares of common stock available for sale under the Prior Cantor Agreement 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 registered under the Securities Act of 1933, as amended. During the six months ended June 30, 2018, 1.8 million shares of the Company’s common stock were sold under the Amended Cantor Agreement for net proceeds of $11.9 million. At June 30, 2018, the Company had approximately $57.8 million of common stock available to be sold under the Amended Cantor Agreement.