Stockholders' Equity	3 Months Ended
Mar. 31, 2020
Equity [Abstract]
Stockholders' Equity	7. Stockholders’ Equity Controlled Equity Offerings Cantor Controlled Equity Offering During the three months ended March 31, 2020, no shares of common stock, respectively, were sold under the Controlled Equity Offering^SM sales agreement, as amended (the “Sales Agreement”), with Cantor Fitzgerald & Co. (“Cantor”), as agent and/or principal. As of March 31, 2020, $43.1 million of common stock remained available to be sold under this facility, subject to certain conditions as specified in the Sales Agreement. Aspire Common Stock Purchase Agreement During the three months ended March 31, 2020, no shares were issued under the Common Stock Purchase Agreement (the “CSPA”) with Aspire Capital Fund, LLC (“Aspire”). Aspire’s remaining purchase commitment was $10.9 million as of March 31, 2020 and Aspire’s obligation under the CSPA will automatically terminate on June 25, 2020.

Stockholders' Equity

3 Months Ended

Mar. 31, 2020

7. Stockholders’ Equity

Controlled Equity Offerings

Cantor Controlled Equity Offering

During the three months ended March 31, 2020, no shares of common stock, respectively, were sold under the Controlled Equity Offering^SM sales agreement, as amended (the “Sales Agreement”), with Cantor Fitzgerald & Co. (“Cantor”), as agent and/or principal. As of March 31, 2020, $43.1 million of common stock remained available to be sold under this facility, subject to certain conditions as specified in the Sales Agreement.

Aspire Common Stock Purchase Agreement

During the three months ended March 31, 2020, no shares were issued under the Common Stock Purchase Agreement (the “CSPA”) with Aspire Capital Fund, LLC (“Aspire”). Aspire’s remaining purchase commitment was $10.9 million as of March 31, 2020 and Aspire’s obligation under the CSPA will automatically terminate on June 25, 2020.