Common Stock	3 Months Ended
Mar. 31, 2018
Equity [Abstract]
Common Stock	8. COMMON STOCK *Common Stock Issued, Net of Issuance Costs* Controlled Equity Offering Sales Agreement with Cantor Fitzgerald (“Cantor”) On April 14, 2017, the Company entered into an at-the-market offer (the “ATM Offering”) with Cantor acting as sales agent. Under the ATM Offering, the Company may from time to time sell shares of its common stock having an aggregate offering amount up to $30.0 million in “at-the-market” offerings, which shares are registered under a registration statement on Form S-3, which was declared effective on March 9, 2017. The Company pays Cantor a commission equal to 2.5% of the gross proceeds from the sale of any shares pursuant to the ATM Offering. As of May 7, 2018, the Company had sold 1,200,565 shares of common stock for net proceeds of $1.4 million under the ATM Offering. As a result, the Company had approximately $28.6 million remaining available for future sales under the ATM Offering. The Company’s previous ATM Offering with BTIG LLC was fully utilized as of December 31, 2016. Common Stock Purchase Agreement (“CSPA”) with Aspire Capital On September 25, 2017, the Company entered into the CSPA with Aspire Capital to place up to $22.0 million in the aggregate of the Company’s common stock on an ongoing basis when required by the Company over a term of 30 months. The Company will control the timing and amount of sales to Aspire Capital, and at a price based on market prices at that time. As consideration for Aspire Capital entering into the purchase agreement, the Company issued 880,000 shares of its common stock to Aspire Capital. The shares of common stock subject to the CSPA were registered pursuant to the Company’s effective shelf registration statement on Form S-3. The parties terminated the April 8, 2016 CSPA with Aspire Capital upon entering into the September 25, 2017 CSPA. On September 27, 2017, pursuant to the CSPA and after satisfaction of certain commencement conditions, Aspire Capital made an initial purchase of 1,428,571 shares of common stock for which the Company received net proceeds of $2.0 million. Additionally, on December 14, 2017, Aspire Capital purchased 150,000 shares of common stock for which the Company received net proceeds of $0.2 million. Finally, as of May 7, 2018, Aspire Capital had purchased 1,951,896 shares pursuant to the agreement for which the Company received net proceeds of $1.1 million. As of May 7, 2018, $18.7 million of the aggregate $22.0 million remained available for future sales under the CSPA, limited by the Exchange Cap to the issuance of no more than an additional 2.7 million shares of common stock unless (i) stockholder approval is obtained, or (ii) the average price paid for all shares issued under the CSPA (including the 880,000 commitment shares) is equal to or greater than $1.38.

Common Stock

3 Months Ended

Mar. 31, 2018

8. COMMON STOCK

Common Stock Issued, Net of Issuance Costs

Controlled Equity Offering Sales Agreement with Cantor Fitzgerald (“Cantor”)

On April 14, 2017, the Company entered into an at-the-market offer (the “ATM Offering”) with Cantor acting as sales agent. Under the ATM Offering, the Company may from time to time sell shares of its common stock having an aggregate offering amount up to $30.0 million in “at-the-market” offerings, which shares are registered under a registration statement on Form S-3, which was declared effective on March 9, 2017. The Company pays Cantor a commission equal to 2.5% of the gross proceeds from the sale of any shares pursuant to the ATM Offering. As of May 7, 2018, the Company had sold 1,200,565 shares of common stock for net proceeds of $1.4 million under the ATM Offering. As a result, the Company had approximately $28.6 million remaining available for future sales under the ATM Offering. The Company’s previous ATM Offering with BTIG LLC was fully utilized as of December 31, 2016.

Common Stock Purchase Agreement (“CSPA”) with Aspire Capital

On September 25, 2017, the Company entered into the CSPA with Aspire Capital to place up to $22.0 million in the aggregate of the Company’s common stock on an ongoing basis when required by the Company over a term of 30 months. The Company will control the timing and amount of sales to Aspire Capital, and at a price based on market prices at that time. As consideration for Aspire Capital entering into the purchase agreement, the Company issued 880,000 shares of its common stock to Aspire Capital. The shares of common stock subject to the CSPA were registered pursuant to the Company’s effective shelf registration statement on Form S-3. The parties terminated the April 8, 2016 CSPA with Aspire Capital upon entering into the September 25, 2017 CSPA.

On September 27, 2017, pursuant to the CSPA and after satisfaction of certain commencement conditions, Aspire Capital made an initial purchase of 1,428,571 shares of common stock for which the Company received net proceeds of $2.0 million. Additionally, on December 14, 2017, Aspire Capital purchased 150,000 shares of common stock for which the Company received net proceeds of $0.2 million. Finally, as of May 7, 2018, Aspire Capital had purchased 1,951,896 shares pursuant to the agreement for which the Company received net proceeds of $1.1 million. As of May 7, 2018, $18.7 million of the aggregate $22.0 million remained available for future sales under the CSPA, limited by the Exchange Cap to the issuance of no more than an additional 2.7 million shares of common stock unless (i) stockholder approval is obtained, or (ii) the average price paid for all shares issued under the CSPA (including the 880,000 commitment shares) is equal to or greater than $1.38.