Stockholders' Equity	9 Months Ended
Sep. 30, 2017
Equity [Abstract]
Stockholders' Equity	Note 9. Stockholders’ Equity Sales Agreement On May 5, 2016, the Company entered into Amendment No. 2 to the Controlled Equity Offering^SM Sales Agreement, dated August 31, 2012, as previously amended on March 21, 2014, (together, the “Amended Cantor Agreement”) with Cantor Fitzgerald & Co. (“Cantor”) that provides 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 over the term of the Amended Cantor Agreement. 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 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 nine months ended September 30, 2017, 7.6 million shares of the Company’s million shares of the Company’s common stock were sold under the Amended Cantor Agreement for net proceeds of $19.3 million. At September 30, 2017, the Company had $42.6 million of common stock available to be sold under Amendment No. 2 to the Amended Cantor Agreement. On August 4, 2017, the Company entered into Amendment No. 3 to the Amended Cantor Agreement. In connection with Amendment No. 3, the Company filed a new shelf registration statement on Form S-3 (the “New Registration Statement”). Amendment No. 3 will become effective upon the effectiveness of the New Registration Statement. As a result of Amendment No. 3, the Amended Cantor Agreement will provide, when effective, 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 following the effectiveness of the New Registration Statement, which amount includes any unsold shares of common stock previously available for sale under the Amended Cantor Agreement. As of September 30, 2017, the New Registration Statement had not been declared effective by the U.S. Securities and Exchange Commission and, as a result, Amendment No. 3 has not become effective.

Note 9. Stockholders’ Equity

Sales Agreement

On May 5, 2016, the Company entered into Amendment No. 2 to the Controlled Equity Offering^SM Sales Agreement, dated August 31, 2012, as previously amended on March 21, 2014, (together, the “Amended Cantor Agreement”) with Cantor Fitzgerald & Co. (“Cantor”) that provides 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 over the term of the Amended Cantor Agreement. 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 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 nine months ended September 30, 2017, 7.6 million shares of the Company’s million shares of the Company’s common stock were sold under the Amended Cantor Agreement for net proceeds of $19.3 million. At September 30, 2017, the Company had $42.6 million of common stock available to be sold under Amendment No. 2 to the Amended Cantor Agreement.

On August 4, 2017, the Company entered into Amendment No. 3 to the Amended Cantor Agreement. In connection with Amendment No. 3, the Company filed a new shelf registration statement on Form S-3 (the “New Registration Statement”). Amendment No. 3 will become effective upon the effectiveness of the New Registration Statement. As a result of Amendment No. 3, the Amended Cantor Agreement will provide, when effective, 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 following the effectiveness of the New Registration Statement, which amount includes any unsold shares of common stock previously available for sale under the Amended Cantor Agreement. As of September 30, 2017, the New Registration Statement had not been declared effective by the U.S. Securities and Exchange Commission and, as a result, Amendment No. 3 has not become effective.